Publications by category
Journal articles
Pacoureau N, Rigby CL, Kyne PM, Sherley RB, Winker H, Carlson JK, Fordham SV, Barreto R, Fernando D, Francis MP, et al (2021). Half a century of global decline in oceanic sharks and rays. Nature, 589(7843), 567-571.
Le Guen C, Suaria G, Sherley RB, Ryan PG, Aliani S, Boehme L, Brierley AS (2020). Microplastic study reveals the presence of natural and synthetic fibres in the diet of King Penguins (Aptenodytes patagonicus) foraging from South Georgia.
Environment International,
134Abstract:
Microplastic study reveals the presence of natural and synthetic fibres in the diet of King Penguins (Aptenodytes patagonicus) foraging from South Georgia
© 2019 the Authors Marine ecosystems are experiencing substantial disturbances due to climate change and overfishing, and plastic pollution is an additional growing threat. Microfibres are among the most pervasive pollutants in the marine environment, including in the Southern Ocean. However, evidence for microfibre contamination in the diet of top predators in the Southern Ocean is rare. King Penguins (Aptenodytes patagonicus) feed on mesopelagic fish, which undergo diel vertical migrations towards the surface at night. Microfibres are concentrated in surface waters and sediments but can also be concentrated in fish, therefore acting as contamination vectors for diving predators feeding at depth. In this study, we investigate microfibre contamination of King Penguin faecal samples collected in February and March 2017 at South Georgia across three groups: incubating, chick-rearing and non-breeding birds. After a KOH digestion to dissolve the organic matter and a density separation step using a NaCl solution, the samples were filtered to collect microfibres. A total of 77% of the penguin faecal samples (36 of 47) contained microfibres. Fibres were measured and characterized using Fourier-Transform Infrared spectroscopy to determine their polymeric identity. Most fibres (88%) were made of natural cellulosic materials (e.g. cotton, linen), with only 12% synthetic (e.g. polyester, nylon) or semi-synthetic (e.g. rayon). An average of 21.9 ± 5.8 microfibres g−1 of faeces (lab dried mass) was found, with concentrations more than twice as high in incubating penguins than in penguins rearing chicks. Incubating birds forage further north at the Antarctic Polar Front and travel longer distances from South Georgia than chick-rearing birds. This suggests that long-distance travelling penguins are probably more exposed to the risk of ingesting microfibres when feeding north of the Antarctic Polar Front, which might act as a semi-permeable barrier for microfibres. Microfibres could therefore provide a signature for foraging location in King Penguins.
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Cook TR, Martin R, Roberts J, Häkkinen H, Botha P, Meyer C, Sparks E, Underhill LG, Ryan PG, Sherley RB, et al (2020). Parenting in a warming world: thermoregulatory responses to heat stress in an endangered seabird.
Conservation Physiology,
8(1).
Abstract:
Parenting in a warming world: thermoregulatory responses to heat stress in an endangered seabird
Abstract
. The frequency of extreme weather events, including heat waves, is increasing with climate change. The thermoregulatory demands resulting from hotter weather can have catastrophic impacts on animals, leading to mass mortalities. Although less dramatic, animals also experience physiological costs below, but approaching, critical temperature thresholds. These costs may be particularly constraining during reproduction, when parents must balance thermoregulation against breeding activities. Such challenges should be acute among seabirds, which often nest in locations exposed to high solar radiation and predation risk. The globally endangered bank cormorant Phalacrocorax neglectus breeds in southern Africa in the winter, giving little scope for poleward or phenological shifts in the face of increasing temperatures. Physiological studies of endangered species sensitive to human disturbance, like the bank cormorant, are challenging, because individuals cannot be captured for experimental research. Using a novel, non-invasive, videographic approach, we investigated the thermoregulatory responses of this seabird across a range of environmental temperatures at three nesting colonies. The time birds spent gular fluttering, a behaviour enhancing evaporative heat loss, increased with temperature. Crouching or standing birds spent considerably less time gular fluttering than birds sitting on nests (ca 30% less at 22°C), showing that postural adjustments mediate exposure to heat stress and enhance water conservation. Crouching or standing, however, increases the vulnerability of eggs and chicks to suboptimal temperatures and/or expose nest contents to predation, suggesting that parents may trade-off thermoregulatory demands against offspring survival. We modelled thermoregulatory responses under future climate scenarios and found that nest-bound bank cormorants will gular flutter almost continuously for several hours a day by 2100. The associated increase in water loss may lead to dehydration, forcing birds to prioritize survival over breeding, a trade-off that would ultimately deteriorate the conservation status of this species.
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Sherley RB, Ladd-Jones H, Garthe S, Stevenson O, Votier SC (2020). Scavenger communities and fisheries waste: North Sea discards support 3 million seabirds, 2 million fewer than in 1990.
Fish and Fisheries,
21(1), 132-145.
Abstract:
Scavenger communities and fisheries waste: North Sea discards support 3 million seabirds, 2 million fewer than in 1990
© 2019 John Wiley. &. Sons Ltd Every year fisheries discard >10 million tonnes of fish. This provides a bounty for scavengers, yet the ecological impact of discarding is understudied. Seabirds are the best-studied discard scavengers and fisheries have shaped their movement ecology, demography and community structure. However, we know little about the number of scavenging seabirds that discards support, how this varies over time or might change as stocks and policy change. Here, we use a Bayesian bioenergetics model to estimate the number of scavenging birds potentially supported by discards in the North Sea (one of the highest discard-producing regions) in 1990, around the peak of production, and again after discard declines in 2010. We estimate that North Sea discards declined by 48% from 509,840 tonnes in 1990 to 267,549 tonnes in 2010. This waste had the potential to support 5.66 (95% credible intervals: 3.33–9.74) million seabirds in the 1990s, declining by 39% to 3.45 (1.98–5.78) million birds by 2010. Our study reveals the potential for fishery discards to support very large scavenging seabird communities but also shows how this has declined over recent decades. Discard bans, like the European Union's Landing Obligation, may reduce inflated scavenger communities, but come against a backdrop of gradual declines potentially buffering deleterious impacts. More work is required to reduce uncertainty and to generate global estimates, but our study highlights the magnitude of scavenger communities potentially supported by discards and thus the importance of understanding the wider ecological consequences of dumping fisheries waste.
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Sherley RB, Crawford RJM, de Blocq AD, Dyer BM, Geldenhuys D, Hagen C, Kemper J, Makhado AB, Pichegru L, Tom D, et al (2020). The conservation status and population decline of the African penguin deconstructed in space and time.
Ecology and Evolution,
10(15).
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The conservation status and population decline of the African penguin deconstructed in space and time
Understanding changes in abundance is crucial for conservation, but population growth rates often vary over space and time. We use 40 years of count data (1979–2019) and Bayesian state-space models to assess the African penguin Spheniscus demersus population under IUCN Red List Criterion A. We deconstruct the overall decline in time and space to identify where urgent conservation action is needed. The global African penguin population met the threshold for Endangered with a high probability (97%), having declined by almost 65% since 1989. An historical low of ~17,700 pairs bred in 2019. Annual changes were faster in the South African population (−4.2%, highest posterior density interval, HPDI: −7.8 to −0.6%) than the Namibian one (−0.3%, HPDI: −3.3 to +2.6%), and since 1999 were almost −10% at South African colonies north of Cape Town. Over the 40-year period, the Eastern Cape colonies went from holding ~25% of the total penguin population to ~40% as numbers decreased more rapidly elsewhere. These changes coincided with an altered abundance and availability of the main prey of African penguins. Our results underline the dynamic nature of population declines in space as well as time and highlight which penguin colonies require urgent conservation attention.
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Lane JV, Jeavons R, Deakin Z, Sherley RB, Pollock CJ, Wanless RJ, Hamer KC (2020). Vulnerability of northern gannets to offshore wind farms; seasonal and sex-specific collision risk and demographic consequences. Marine Environmental Research, 162, 105196-105196.
Sherley RB, Winker H, Rigby CL, Kyne PM, Pollom R, Pacoureau N, Herman K, Carlson JK, Yin JS, Kindsvater HK, et al (2019). Estimating IUCN Red List population reduction: JARA—A decision‐support tool applied to pelagic sharks.
Conservation Letters,
13(2).
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Crawford RJM, Sydeman WJ, Thompson SA, Sherley R, Makhado AB (2019). Food habits of an endangered seabird indicate recent poor forage fish availability. ICES Journal of Marine Science, 76, 1344-1352.
Dyer BM, Cooper J, Crawford RJM, Sherley RB, Somhlaba S, Cockcroft A, Upfold L, Makhado AB (2019). Geographical and temporal variation in the diet of Bank Cormorants Phalacrocorax neglectus in South Africa.
Ostrich,
90(4), 373-390.
Abstract:
Geographical and temporal variation in the diet of Bank Cormorants Phalacrocorax neglectus in South Africa
© 2019, © 2019 NISC (Pty) Ltd. The Bank Cormorant Phalacrocorax neglectus is endemic to the Benguela upwelling ecosystem off southwest Africa and is classified as Endangered owing to a recent large reduction in its number. It is thought that food scarcity, including a decreased abundance of West Coast rock lobster Jasus lalandii, has been a major driver of the decrease, yet its diet in South Africa is poorly known. We collected 941 pellets regurgitated by Bank Cormorants, at 18 South African breeding colonies during 1975–1985, and 1 523 pellets at 17 colonies during 1995–2002. The species composition of the diet (% numbers) was significantly different between the two periods, with widespread decreases in proportions of rock lobster in the west and of octopus and cuttlefish Sepia spp. at most localities. These taxa were replaced in the diet by fish, including Gobiidae and Clinidae. The pelagic goby Sufflogobius bibarbatus, an important prey of Bank Cormorants in Namibia, was absent from pellets collected in 1975–1985 but common at northern localities from 1995–2002. Composition of the diet by frequency of occurrence was only determined for 1995–2002, when rock lobster was present in 67% of all samples collected, cuttlefish in 39%, and Clinidae in 32%. Data for 1975–1985 and 1995–2002 showed that carapace lengths of rock lobsters eaten by Bank Cormorants averaged 56 mm (range 22–82 mm) and 50 mm (range 22–75 mm), respectively, which compares to the minimum legal size of 75 mm for fisheries in South Africa. This energy- rich prey item was an important constituent of the diet in the winter breeding period.
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Ropert-Coudert Y, Chiaradia A, Ainley D, Barbosa A, Boersma PD, Brasso R, Dewar M, Ellenberg U, Garcia-Borboroglu P, Emmerson L, et al (2019). Happy Feet in a Hostile World? the Future of Penguins Depends on Proactive Management of Current and Expected Threats.
FRONTIERS IN MARINE SCIENCE,
6 Author URL.
Ropert-Coudert Y, Chiaradia A, Ainley D, Barbosa A, Boersma PD, Brasso R, Dewar M, Ellenberg U, García-Borboroglu P, Emmerson L, et al (2019). Happy feet in a hostile world? the future of penguins depends on proactive management of current and expected threats.
Frontiers in Marine Science,
6(May).
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Happy feet in a hostile world? the future of penguins depends on proactive management of current and expected threats
© 2019 Ropert-Coudert, Chiaradia, Ainley, Barbosa, Boersma, Brasso, Dewar, Ellenberg, García-Borboroglu, Emmerson, Hickcox, Jenouvrier, Kato, McIntosh, Lewis, Ramírez, Ruoppolo, Ryan, Seddon, Sherley, Vanstreels, Waller, Woehler and Trathan. Penguins face a wide range of threats. Most observed population changes have been negative and have happened over the last 60 years. Today, populations of 11 penguin species are decreasing. Here we present a review that synthesizes details of threats faced by the world's 18 species of penguins. We discuss alterations to their environment at both breeding sites on land and at sea where they forage. The major drivers of change appear to be climate, and food web alterations by marine fisheries. In addition, we also consider other critical and/or emerging threats, namely human disturbance near nesting sites, pollution due to oil, plastics and chemicals such as mercury and persistent organic compounds. Finally, we assess the importance of emerging pathogens and diseases on the health of penguins. We suggest that in the context of climate change, habitat degradation, introduced exotic species and resource competition with fisheries, successful conservation outcomes will require new and unprecedented levels of science and advocacy. Successful conservation stories of penguin species across their geographical range have occurred where there has been concerted effort across local, national and international boundaries to implement effective conservation planning.
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Winker H, Sherley R (2019). JARA: 'Just Another Red-List Assessment'.
bioRxiv, 672899-672899.
Abstract:
JARA: 'Just Another Red-List Assessment'
Identifying species at risk of extinction is necessary to prioritise conservation efforts. The International Union for Conservation of Nature's (IUCN) Red List of Threatened Species is the global standard for quantifying extinction risk, with many species categorised on the basis of a reduction in population size. We introduce the Bayesian state-space framework 'JARA' (Just Another Red-List Assessment). Designed as decision-support tool, JARA allows both process error and uncertainty to be incorporated into IUCN Red List assessments under criterion A. JARA outputs easy to interpret graphics showing the posterior probability of the population decline displayed against the IUCN Red List categories, and assigns each category an associated probability given process and observation uncertainty. JARA is designed to be easy to use, rapid and widely applicable, so conservation practitioners can apply it to their own count or relative abundance data. We illustrate JARA using three real-world examples: (1) relative abundance indices for two elasmobranchs, Yellowspotted Skate Leucoraja wallacei and Whitespot Smoothhound Mustelus palumbes; (2) a comparison of standardized abundance indices for Atlantic Blue Marlin Makaira nigricans and (3) absolute abundance data for Cape Gannets Morus capensis. Finally, using a simulation experiment, we demonstrate how JARA provides greater accuracy than two approaches commonly used to assigning a Red List Status under criterion A. Tools like JARA can help further standardise Red List evaluations, increasing objectivity and lowering the risk of misclassification. The consequences for global conservation efforts could be substantial.
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Campbell KJ, Steinfurth A, Underhill LG, Coetzee JC, Dyer BM, Ludynia K, Makhado AB, Merkle D, Rademan J, Upfold L, et al (2019). Local forage fish abundance influences foraging effort and offspring condition in an endangered marine predator.
Journal of Applied Ecology,
56(7), 1751-1760.
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Deakin Z, Hamer KC, Sherley RB, Bearhop S, Bodey TW, Clark BL, James Grecian W, Gummery M, Lane J, Morgan G, et al (2019). Sex differences in migration and demography of a wide-ranging seabird, the Northern Gannet.
Marine Ecology Progress Series,
622, 191-201.
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Sex differences in migration and demography of a wide-ranging seabird, the Northern Gannet
© the authors 2019. Marine vertebrates show a diversity of migration strategies, including sex differences. This may lead to differential demography, but the consequences of such between-sex variation are little understood. Here, we studied the migration of known-sex northern gannets Morus bassanus — a partial migrant with females ~8 % heavier than males. We used geolocators to determine wintering areas of 49 breeding adults (19 females and 30 males during 2010 to 2014) from 2 colonies in the northeast Atlantic (Bass Rock and Grassholm, UK). We also tested for sex-specific survival probabilities using capture−mark−recapture methods (n = 72 individuals Bass Rock, n = 229 individuals Grassholm; 2010−2018) and applied sex-specific population projection matrices (PPMs) to quantify population-level effects. Tracked gannets wintered in a range of large marine ecosystems (LMEs): Canary Current LME (CCLME; 69 %), Celtic-Biscay Shelf LME (16 %), Iberian Coastal LME (8 %), North Sea LME (4 %) or Mediterranean LME (2 %). Migratory destination differed between the sexes: 90 % of females vs. 57 % of males wintered in the CCLME. Survival was similar between the sexes at Bass Rock (mean ± 95 % CI = 0.951 ± 0.053 and 0.956 ± 0.047 for females and males, respectively). At Grassholm, there was evidence of slight sex differences in breeder survival: females had lower annual survival (0.882 ± 0.040) than males (0.946 ± 0.026). At Bass Rock, PPMs with no sex effect best fitted the observed population increase (1994−2014). Sex-specific PPMs fitted the population estimates for Grassholm (1995−2015). Our results reveal that female gannets are more likely to travel further than males to winter in the CCLME. This difference is unlikely due to morphological differences, unlike in other bird species. However, the reason for slightly higher over-winter female mortality at Grassholm is unclear.
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Gianuca D, Votier SC, Pardo D, Wood AG, Sherley RB, Ireland L, Choquet R, Pradel R, Townley S, Forcada J, et al (2019). Sex‐specific effects of fisheries and climate on the demography of sexually dimorphic seabirds. Journal of Animal Ecology, 88(9), 1366-1378.
Sherley RB, Crawford RJM, Dyer BM, Kemper J, Makhado AB, Masotla M, Pichegru L, Pistorius PA, Roux JP, Ryan PG, et al (2019). The status and conservation of the Cape Gannet Morus capensis.
Ostrich,
90(4), 335-346.
Abstract:
The status and conservation of the Cape Gannet Morus capensis
© 2019, © 2019 NISC (Pty) Ltd. The Cape Gannet Morus capensis is one of several seabird species endemic to the Benguela upwelling ecosystem (BUS) but whose population has recently decreased, leading to an unfavourable IUCN Red List assessment. Application of ‘JARA’ (‘Just Another Red-List Assessment,’ a Bayesian state-space tool used for IUCN Red List assessments) to updated information on the areas occupied by Cape Gannets and the nest densities of breeding birds at their six colonies, suggested that the species should be classified as Vulnerable. However, the rate of decrease of Cape Gannets in their most-recent generation exceeded that of the previous generation, primarily as a result of large decreases at Bird Island, Lambert’s Bay, and Malgas Island, off South Africa’s west coast (the western part of their range). Since the 1960s, there has been an ongoing redistribution of the species from northwest to southeast around southern Africa, and ∼70% of the population now occurs on the south coast of South Africa, at Bird Island in Algoa Bay, on the eastern border of the BUS. Recruitment rather than adult survival may be limiting the present population; however, information on the seabird’s demographic parameters and mortality in fisheries is lacking for colonies in the northern part of the BUS. Presently, major threats to Cape Gannet include: substantially decreased availability of their preferred prey in the west; heavy mortalities of eggs, chicks and fledglings at and around colonies, inflicted by Cape Fur Seals Arctocephalus pusillus and other seabirds; substantial disturbance at colonies caused by Cape Fur Seals attacking adult gannets ashore; oiling; and disease.
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Gaglio D, Sherley RB, Ryan PG, Cook TR (2018). A non-invasive approach to estimate the energetic requirements of an increasing seabird population in a perturbed marine ecosystem.
Scientific Reports,
8(1).
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Sherley RB, Barham BJ, Barham PJ, Campbell KJ, Crawford RJM, Grigg J, Horswill C, McInnes A, Morris TL, Pichegru L, et al (2018). Bayesian inference reveals positive but subtle effects of experimental fishery closures on marine predator demographics.
Proceedings of the Royal Society B: Biological Sciences,
285(1871), 20172443-20172443.
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Bayesian inference reveals positive but subtle effects of experimental fishery closures on marine predator demographics
. Global forage-fish landings are increasing, with potentially grave consequences for marine ecosystems. Predators of forage fish may be influenced by this harvest, but the nature of these effects is contentious. Experimental fishery manipulations offer the best solution to quantify population-level impacts, but are rare. We used Bayesian inference to examine changes in chick survival, body condition and population growth rate of endangered African penguins
. Spheniscus demersus
. in response to 8 years of alternating time–area closures around two pairs of colonies. Our results demonstrate that fishing closures improved chick survival and condition, after controlling for changing prey availability. However, this effect was inconsistent across sites and years, highlighting the difficultly of assessing management interventions in marine ecosystems. Nevertheless, modelled increases in population growth rates exceeded 1% at one colony; i.e. the threshold considered biologically meaningful by fisheries management in South Africa. Fishing closures evidently can improve the population trend of a forage-fish-dependent predator—we therefore recommend they continue in South Africa and support their application elsewhere. However, detecting demographic gains for mobile marine predators from small no-take zones requires experimental time frames and scales that will often exceed those desired by decision makers.
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Gaglio D, Cook TR, McInnes A, Sherley RB, Ryan PG (2018). Foraging plasticity in seabirds: a non-invasive study of the diet of greater crested terns breeding in the Benguela region.
PLoS ONE,
13(1).
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Foraging plasticity in seabirds: a non-invasive study of the diet of greater crested terns breeding in the Benguela region
© 2018 Gaglio et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Marine predators, such as seabirds, are useful indicators of marine ecosystem functioning. In particular, seabird diet may reflect variability in food-web composition due to natural or human-induced environmental change. Diet monitoring programmes, which sample diet non-invasively, are valuable aids to conservation and management decision-making. We investigated the diet of an increasing population of greater crested terns Thalasseus bergii in the Western Cape, South Africa, during three successive breeding seasons (2013 to 2015), when populations of other seabirds feeding on small pelagic schooling fish in the region were decreasing. Breeding greater crested terns carry prey in their bills, so we used an intensive photo-sampling method to record their diet with little disturbance. We identified 24,607 prey items from at least 47 different families, with 34 new prey species recorded. Fish dominated the diet, constituting 94% of prey by number, followed by cephalopods (3%), crustaceans (2%) and insects (1%). The terns mainly targeted surface-schooling Clupeiformes, with anchovy Engraulis encrasicolus the most abundant prey in all three breeding seasons (65% overall). Prey composition differed significantly between breeding stages and years, with anchovy most abundant at the start of the breeding season, becoming less frequent as the season progressed. The proportion of anchovy in the diet also was influenced by environmental factors; anchovy occurred more frequently with increasing wind speeds and was scarce on foggy days, presumably because terns rely in part on social facilitation to locate anchovy schools. The application of this intensive and non-invasive photo-sampling method revealed an important degree of foraging plasticity for this seabird within a context of locally reduced food availability, suggesting that, unlike species that specialise on a few high-quality prey, opportunistic seabirds may be better able to cope with reductions in the abundance of their preferred prey.
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Gaglio D, Cook TR, Sherley RB, Ryan PG (2018). How many can you catch? Factors influencing the occurrence of multi-prey loading in provisioning Greater Crested Terns.
Ostrich,
89(2), 145-149.
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Payo-Payo A, Sanz-Aguilar A, Gaglio D, Sherley RB, Cook TR, Altwegg R, Ryan PG (2018). Survival estimates for the greater crested tern Thalasseus bergii in southern Africa.
African Journal of Marine Science,
40(1), 43-50.
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Survival estimates for the greater crested tern Thalasseus bergii in southern Africa
© 2018 NISC (Pty) Ltd. The nominate race of the greater crested tern Thalasseus bergii breeds only along the coast of the Benguela region (west coast) of southern Africa, where its population is increasing, in contrast to other species of breeding seabirds in the region which similarly depend on forage fish. Although this population’s trends are well known, its demographic parameters remain obscure. We used multi-event capture–recapture–recovery modelling to provide the first estimates of survival. The survival rate of birds older than two years was 0.93 (0.91–0.95); second-year survival was 0.93 (0.90–0.95) and first-year survival was 0.80 (0.73–0.85). A resighting of a 34-year-old bird is a new longevity record for the species. Population growth rates projected with a Leslie matrix model that included our survival estimates were very similar to estimates from annual counts of the breeding population (7–8% y−1), suggesting that these survival estimates adequately describe the species’ demography. High survival rates have likely contributed to the species’ recent population increase in the region.
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Gaglio D, Sherley RB, Cook TR, Ryan PG, Flower T (2018). The costs of kleptoparasitism: a study of mixed-species seabird breeding colonies.
Behavioral Ecology,
29(4), 939-947.
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Sydeman WJ, Thompson SA, Anker-Nilssen T, Arimitsu M, Bennison A, Bertrand S, Boersch-Supan P, Boyd C, Bransome NC, Crawford RJM, et al (2017). Best practices for assessing forage fish fisheries-seabird resource competition.
Fisheries Research,
194, 209-221.
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Best practices for assessing forage fish fisheries-seabird resource competition
© 2017 Elsevier B.V. Worldwide, in recent years capture fisheries targeting lower-trophic level forage fish and euphausiid crustaceans have been substantial (∼20 million metric tons [MT] annually). Landings of forage species are projected to increase in the future, and this harvest may affect marine ecosystems and predator-prey interactions by removal or redistribution of biomass central to pelagic food webs. In particular, fisheries targeting forage fish and euphausiids may be in competition with seabirds, likely the most sensitive of marine vertebrates given limitations in their foraging abilities (ambit and gape size) and high metabolic rate, for food resources. Lately, apparent competition between fisheries and seabirds has led to numerous high-profile conflicts over interpretations, as well as the approaches that could and should be used to assess the magnitude and consequences of fisheries-seabird resource competition. In this paper, we review the methods used to date to study fisheries competition with seabirds, and present “best practices” for future resource competition assessments. Documenting current fisheries competition with seabirds generally involves addressing two major issues: 1) are fisheries causing localized prey depletion that is sufficient to affect the birds? (i.e. are fisheries limiting food resources?), and 2) how are fisheries-induced changes to forage stocks affecting seabird populations given the associated functional or numerical response relationships? Previous studies have been hampered by mismatches in the scale of fisheries, fish, and seabird data, and a lack of causal understanding due to confounding by climatic and other ecosystem factors (e.g. removal of predatory fish). Best practices for fisheries-seabird competition research should include i) clear articulation of hypotheses, ii) data collection (or summation) of fisheries, fish, and seabirds on matched spatio-temporal scales, and iii) integration of observational and experimental (including numerical simulation) approaches to establish connections and causality between fisheries and seabirds. As no single technique can provide all the answers to this vexing issue, an integrated approach is most promising to obtain robust scientific results and in turn the sustainability of forage fish fisheries from an ecosystem perspective.
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Morten JM, Parsons NJ, Schwitzer C, Holderied MW, Sherley RB (2017). Body condition as a quantitative tool to guide hand-rearing decisions in an endangered seabird.
Animal Conservation,
20(5), 471-479.
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Body condition as a quantitative tool to guide hand-rearing decisions in an endangered seabird
© 2017 the Zoological Society of London the use of wildlife rehabilitation for conservation is growing, but quantitative criteria are rarely used to guide whether and when to remove animals from the wild. Since 2006, large numbers of African penguin Spheniscus demersus chicks have been abandoned annually when adults enter moult with dependent young still in the nest. As part of conservation initiatives for this endangered species, these chicks were collected and hand reared to fledging age. Post-release survival has been well documented; in this study we develop models to predict survival of individuals during rehabilitation with the aim of improving hand-rearing success and guiding the use of scarce resources. For 1455 chicks abandoned between 2008 and 2013, we assessed whether a chick body condition index (BCI) could predict outcome (death or release) and time spent in rearing. In addition, for a subset of 173 chicks in 2012, we assessed whether BCI at admission influenced chick growth rates during rehabilitation and examined whether the use of additional structural measurements and sex provided additional power to predict outcome. Models predicted an 82.9% (95% confidence interval: 73.3–89.5%) release rate for chicks admitted with a BCI >0, the proposed guideline for removal from colonies. This fell below 50% for BCIs
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Sherley RB, Botha P, Underhill LG, Ryan PG, van Zyl D, Cockcroft AC, Crawford RJM, Dyer BM, Cook TR (2017). Defining ecologically relevant scales for spatial protection with long-term data on an endangered seabird and local prey availability.
Conservation Biology,
31(6), 1312-1321.
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Defining ecologically relevant scales for spatial protection with long-term data on an endangered seabird and local prey availability
© 2017 Society for Conservation Biology Human activities are important drivers of marine ecosystem functioning. However, separating the synergistic effects of fishing and environmental variability on the prey base of nontarget predators is difficult, often because prey availability estimates on appropriate scales are lacking. Understanding how prey abundance at different spatial scales links to population change can help integrate the needs of nontarget predators into fisheries management by defining ecologically relevant areas for spatial protection. We investigated the local population response (number of breeders) of the Bank Cormorant (Phalacrocorax neglectus), a range-restricted endangered seabird, to the availability of its prey, the heavily fished west coast rock lobster (Jasus lalandii). Using Bayesian state-space modeled cormorant counts at 3 colonies, 22 years of fisheries-independent data on local lobster abundance, and generalized additive modeling, we determined the spatial scale pertinent to these relationships in areas with different lobster availability. Cormorant numbers responded positively to lobster availability in the regions with intermediate and high abundance but not where regime shifts and fishing pressure had depleted lobster stocks. The relationships were strongest when lobsters 20–30 km offshore of the colony were considered, a distance greater than the Bank Cormorant's foraging range when breeding, and may have been influenced by prey availability for nonbreeding birds, prey switching, or prey ecology. Our results highlight the importance of considering the scale of ecological relationships in marine spatial planning and suggest that designing spatial protection around focal species can benefit marine predators across their full life cycle. We propose the precautionary implementation of small-scale marine protected areas, followed by robust assessment and adaptive-management, to confirm population-level benefits for the cormorants, their prey, and the wider ecosystem, without negative impacts on local fisheries.
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Gaglio D, Cook TR, Connan M, Ryan PG, Sherley RB (2017). Dietary studies in birds: testing a non-invasive method using digital photography in seabirds.
Methods in Ecology and Evolution,
8(2), 214-222.
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Dietary studies in birds: testing a non-invasive method using digital photography in seabirds
© 2016 the Authors. Methods in Ecology and Evolution © 2016 British Ecological Society Dietary studies give vital insights into foraging behaviour, with implications for understanding changing environmental conditions and the anthropogenic impacts on natural resources. Traditional diet sampling methods may be invasive or subject to biases, so developing non-invasive and unbiased methods applicable to a diversity of species is essential. We used digital photography to investigate the diet fed to chicks of a prey-carrying seabird and compared our approach (photo-sampling) to a traditional method (regurgitations) for the greater crested tern Thalasseus bergii. Over three breeding seasons, we identified >24 000 prey items of at least 48 different species, more than doubling the known diversity of prey taken by this population of terns. We present a method to estimate the length of the main prey species (anchovy Engraulis encrasicolus) from photographs, with an accuracy
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Gaglio D, Sherley R, Cook T (2017). Insects in the diet of the Greater Crested Tern Thalasseus bergii bergii in Southern Africa. Marine Ornithology, 43, 131-132.
Sherley RB, Ludynia K, Dyer BM, Lamont T, Makhado AB, Roux J-P, Scales KL, Underhill LG, Votier SC (2017). Metapopulation Tracking Juvenile Penguins Reveals an Ecosystem-wide Ecological Trap.
Current Biology,
27(4), 563-568.
Full text.
Sherley RB (2017). PhD jobs: Revamp funding structures.
Nature,
551(7681).
Full text.
Brisson-Curadeau É, Bird D, Burke C, Fifield DA, Pace P, Sherley RB, Elliott KH (2017). Seabird species vary in behavioural response to drone census.
Scientific Reports,
7(1).
Abstract:
Seabird species vary in behavioural response to drone census
© 2017 the Author(s). Unmanned aerial vehicles (UAVs) provide an opportunity to rapidly census wildlife in remote areas while removing some of the hazards. However, wildlife may respond negatively to the UAVs, thereby skewing counts. We surveyed four species of Arctic cliff-nesting seabirds (glaucous gull Larus hyperboreus, Iceland gull Larus glaucoides, common murre Uria aalge and thick-billed murre Uria lomvia) using a UAV and compared censusing techniques to ground photography. An average of 8.5% of murres flew off in response to the UAV, but >99% of those birds were non-breeders. We were unable to detect any impact of the UAV on breeding success of murres, except at a site where aerial predators were abundant and several birds lost their eggs to predators following UAV flights. Furthermore, we found little evidence for habituation by murres to the UAV. Most gulls flew off in response to the UAV, but returned to the nest within five minutes. Counts of gull nests and adults were similar between UAV and ground photography, however the UAV detected up to 52.4% more chicks because chicks were camouflaged and invisible to ground observers. UAVs provide a less hazardous and potentially more accurate method for surveying wildlife. We provide some simple recommendations for their use.
Abstract.
Full text.
Votier SC, Sherley RB (2017). Seabirds. Current Biology, 27(11), R448-R450.
Crawford R, Ellenberg U, Frere E, Hagen C, Baird K, Brewin P, Crofts S, Glass J, Mattern T, Pompert J, et al (2017). Tangled and drowned: a global review of penguin bycatch in fisheries. Endangered Species Research, 34, 373-396.
Sherley RB, Barham BJ, Barham PJ, Leshoro TM, Underhill LG (2016). Artificial nests enhance the breeding productivity of African Penguins (Spheniscus demersus) on Robben Island, South Africa. Emu - Austral Ornithology, 112(2), 97-106.
Weller F, Sherley RB, Shannon LJ, Jarre A, Stewart T, Scott L, Altwegg R, Cecchini LA, Crawford RJM, Geldenhuys D, et al (2016). Penguins' perilous conservation status calls for complementary approach based on sound ecological principles: reply to Butterworth et al. (2015). Ecological Modelling, 337, 1-3.
Weller F, Sherley RB, Waller LJ, Ludynia K, Geldenhuys D, Shannon LJ, Jarre A (2016). System dynamics modelling of the Endangered African penguin populations on Dyer and Robben islands, South Africa.
Ecological Modelling,
327, 44-56.
Abstract:
System dynamics modelling of the Endangered African penguin populations on Dyer and Robben islands, South Africa
© 2016 Elsevier B.V. African penguins (Spheniscus demersus) in South Africa have been subject to rapid decline in the 20th century and are currently listed as "endangered" on the IUCN Red List. A stochastic, stage-specific system dynamics model with spatial components was developed to investigate the interaction of multiple pressures on penguin population development, and originally applied to study conservation management options for the penguin colony at Robben Island, Table Bay, South Africa. We here present an extension of the model to the nearby colony at Dyer Island. The modelled population was found to be strongly dominated by the effects of Cape fur seal (Arctocephalus pusillus pusillus) predation and immature emigration, which appear to be key drivers behind current declines in population numbers at this colony. Chronic low-level oiling also had a consistent impact despite ongoing mitigation measures, while kelp gull predation had a lower effect than expected. At current low population size, the pressure from either seal predation or immature emigration seems sufficient to mask any beneficial effects to penguins from possible improvements in available food biomass (e.g. from fishery restrictions). Results suggest that conservation management at this colony should focus on regular culling of predating seals combined with improving availability of prey (thus discouraging emigration) both in the foraging range of breeding penguins and in their general foraging area. Our findings demonstrate the use of site-specific scenario tools to explore conservation strategies in data-poor management situations.
Abstract.
Sherley RB, Winker H, Altwegg R, van der Lingen CD, Votier SC, Crawford RJM (2015). Bottom-up effects of a no-take zone on endangered penguin demographics.
Biology Letters,
11(7), 20150237-20150237.
Abstract:
Bottom-up effects of a no-take zone on endangered penguin demographics
. Marine no-take zones can have positive impacts for target species and are increasingly important management tools. However, whether they indirectly benefit higher order predators remains unclear. The endangered African penguin (
. Spheniscus demersus
. ) depends on commercially exploited forage fish. We examined how chick survival responded to an experimental 3-year fishery closure around Robben Island, South Africa, controlling for variation in prey biomass and fishery catches. Chick survival increased by 18% when the closure was initiated, which alone led to a predicted 27% higher population compared with continued fishing. However, the modelled population continued to decline, probably because of high adult mortality linked to poor prey availability over larger spatial scales. Our results illustrate that small no-take zones can have bottom-up benefits for highly mobile marine predators, but are only one component of holistic, ecosystem-based management regimes.
.
Abstract.
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Gaglio D, Cook TR, Sherley RB (2015). Egg morphology of Swift Terns in South Africa. Ostrich, 86(3), 287-289.
Weller F, Cecchini L-A, Shannon L, Sherley RB, Crawford RJM, Altwegg R, Scott L, Stewart T, Jarre A (2014). A system dynamics approach to modelling multiple drivers of the African penguin population on Robben Island, South Africa. Ecological Modelling, 277, 38-56.
Sherley RB, Abadi F, Ludynia K, Barham BJ, Clark AE, Altwegg R (2014). Age-specific survival and movement among major African PenguinSpheniscus demersuscolonies. Ibis, 156(4), 716-728.
Sherley RB, Waller LJ, Strauss V, Geldenhuys D, Underhill LG, Parsons NJ (2014). Hand-Rearing, Release and Survival of African Penguin Chicks Abandoned Before Independence by Moulting Parents. PLoS ONE, 9(10), e110794-e110794.
Ludynia K, Waller LJ, Sherley RB, Abadi F, Galada Y, Geldenhuys D, Crawford RJM, Shannon LJ, Jarre A (2014). Processes influencing the population dynamics and conservation of African penguins on Dyer Island, South Africa. African Journal of Marine Science, 36(2), 253-267.
Sherley RB, Barham PJ, Barham BJ, Crawford RJM, Dyer BM, Leshoro TM, Makhado AB, Upfold L, Underhill LG (2013). Growth and decline of a penguin colony and the influence on nesting density and reproductive success. Population Ecology, 56(1), 119-128.
Sherley RB, Underhill LG, Barham BJ, Barham PJ, Coetzee JC, Crawford RJM, Dyer BM, Leshoro TM, Upfold L (2013). Influence of local and regional prey availability on breeding performance of African penguins Spheniscus demersus. Marine Ecology Progress Series, 473, 291-301.
Bonato M, Evans MR, Hasselquist D, Sherley RB, Cloete SWP, Cherry MI (2013). Ostrich chick humoral immune responses and growth rate are predicted by parental immune responses and paternal colouration. Behavioral Ecology and Sociobiology, 67(12), 1891-1901.
Sherley RB, Ludynia K, Lamont T, Roux JP, Crawford RJM, Underhill LG (2013). The initial journey of an Endangered penguin: implications for seabird conservation. Endangered Species Research, 21(1), 89-95.
Sherley RB, Ludynia K, Underhill LG, Jones R, Kemper J (2011). Storms and heat limit the nest success of Bank Cormorants: implications of future climate change for a surface-nesting seabird in southern Africa. Journal of Ornithology, 153(2), 441-455.
Villiers MSD, Mecenero S, Sherley RB, Heinze E, Kieser J, Leshoro TM, Merbold L, Nordt A, Parsons NJ, Peter H-U, et al (2010). Introduced European Rabbits (Oryctolagus cuniculus) and Domestic Cats (Felis catus) on Robben Island: Population Trends and Management Recommendations. South African Journal of Wildlife Research, 40(2), 139-148.
Sherley RB, Burghardt T, Barham PJ, Campbell N, Cuthill IC (2010). Spotting the difference: towards fully-automated population monitoring of African penguins Spheniscus demersus. Endangered Species Research, 11, 101-111.
Underhill LG, Sherley RB, Dyer BM, Crawford RJM (2009). Interactions between snakes and seabirds on Robben, Schaapen and Meeuw Islands, Western Cape province, South Africa.
OSTRICH,
80(2), 115-118.
Author URL.
Chapters
Provencher JF, Borrelle S, Sherley RB, Avery-Gomm S, Hodum P, Bond A, Major HL, McCoy KD, Crawford R, Merkel F, et al (2018). Seabirds. In (Ed)
World Seas: an Environmental Evaluation Volume III: Ecological Issues and Environmental Impacts, 133-162.
Abstract:
Seabirds
Abstract.
Publications by year
2021
Pacoureau N, Rigby CL, Kyne PM, Sherley RB, Winker H, Carlson JK, Fordham SV, Barreto R, Fernando D, Francis MP, et al (2021). Half a century of global decline in oceanic sharks and rays. Nature, 589(7843), 567-571.
2020
Le Guen C, Suaria G, Sherley RB, Ryan PG, Aliani S, Boehme L, Brierley AS (2020). Microplastic study reveals the presence of natural and synthetic fibres in the diet of King Penguins (Aptenodytes patagonicus) foraging from South Georgia.
Environment International,
134Abstract:
Microplastic study reveals the presence of natural and synthetic fibres in the diet of King Penguins (Aptenodytes patagonicus) foraging from South Georgia
© 2019 the Authors Marine ecosystems are experiencing substantial disturbances due to climate change and overfishing, and plastic pollution is an additional growing threat. Microfibres are among the most pervasive pollutants in the marine environment, including in the Southern Ocean. However, evidence for microfibre contamination in the diet of top predators in the Southern Ocean is rare. King Penguins (Aptenodytes patagonicus) feed on mesopelagic fish, which undergo diel vertical migrations towards the surface at night. Microfibres are concentrated in surface waters and sediments but can also be concentrated in fish, therefore acting as contamination vectors for diving predators feeding at depth. In this study, we investigate microfibre contamination of King Penguin faecal samples collected in February and March 2017 at South Georgia across three groups: incubating, chick-rearing and non-breeding birds. After a KOH digestion to dissolve the organic matter and a density separation step using a NaCl solution, the samples were filtered to collect microfibres. A total of 77% of the penguin faecal samples (36 of 47) contained microfibres. Fibres were measured and characterized using Fourier-Transform Infrared spectroscopy to determine their polymeric identity. Most fibres (88%) were made of natural cellulosic materials (e.g. cotton, linen), with only 12% synthetic (e.g. polyester, nylon) or semi-synthetic (e.g. rayon). An average of 21.9 ± 5.8 microfibres g−1 of faeces (lab dried mass) was found, with concentrations more than twice as high in incubating penguins than in penguins rearing chicks. Incubating birds forage further north at the Antarctic Polar Front and travel longer distances from South Georgia than chick-rearing birds. This suggests that long-distance travelling penguins are probably more exposed to the risk of ingesting microfibres when feeding north of the Antarctic Polar Front, which might act as a semi-permeable barrier for microfibres. Microfibres could therefore provide a signature for foraging location in King Penguins.
Abstract.
Cook TR, Martin R, Roberts J, Häkkinen H, Botha P, Meyer C, Sparks E, Underhill LG, Ryan PG, Sherley RB, et al (2020). Parenting in a warming world: thermoregulatory responses to heat stress in an endangered seabird.
Conservation Physiology,
8(1).
Abstract:
Parenting in a warming world: thermoregulatory responses to heat stress in an endangered seabird
Abstract
. The frequency of extreme weather events, including heat waves, is increasing with climate change. The thermoregulatory demands resulting from hotter weather can have catastrophic impacts on animals, leading to mass mortalities. Although less dramatic, animals also experience physiological costs below, but approaching, critical temperature thresholds. These costs may be particularly constraining during reproduction, when parents must balance thermoregulation against breeding activities. Such challenges should be acute among seabirds, which often nest in locations exposed to high solar radiation and predation risk. The globally endangered bank cormorant Phalacrocorax neglectus breeds in southern Africa in the winter, giving little scope for poleward or phenological shifts in the face of increasing temperatures. Physiological studies of endangered species sensitive to human disturbance, like the bank cormorant, are challenging, because individuals cannot be captured for experimental research. Using a novel, non-invasive, videographic approach, we investigated the thermoregulatory responses of this seabird across a range of environmental temperatures at three nesting colonies. The time birds spent gular fluttering, a behaviour enhancing evaporative heat loss, increased with temperature. Crouching or standing birds spent considerably less time gular fluttering than birds sitting on nests (ca 30% less at 22°C), showing that postural adjustments mediate exposure to heat stress and enhance water conservation. Crouching or standing, however, increases the vulnerability of eggs and chicks to suboptimal temperatures and/or expose nest contents to predation, suggesting that parents may trade-off thermoregulatory demands against offspring survival. We modelled thermoregulatory responses under future climate scenarios and found that nest-bound bank cormorants will gular flutter almost continuously for several hours a day by 2100. The associated increase in water loss may lead to dehydration, forcing birds to prioritize survival over breeding, a trade-off that would ultimately deteriorate the conservation status of this species.
Abstract.
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Sherley RB, Ladd-Jones H, Garthe S, Stevenson O, Votier SC (2020). Scavenger communities and fisheries waste: North Sea discards support 3 million seabirds, 2 million fewer than in 1990.
Fish and Fisheries,
21(1), 132-145.
Abstract:
Scavenger communities and fisheries waste: North Sea discards support 3 million seabirds, 2 million fewer than in 1990
© 2019 John Wiley. &. Sons Ltd Every year fisheries discard >10 million tonnes of fish. This provides a bounty for scavengers, yet the ecological impact of discarding is understudied. Seabirds are the best-studied discard scavengers and fisheries have shaped their movement ecology, demography and community structure. However, we know little about the number of scavenging seabirds that discards support, how this varies over time or might change as stocks and policy change. Here, we use a Bayesian bioenergetics model to estimate the number of scavenging birds potentially supported by discards in the North Sea (one of the highest discard-producing regions) in 1990, around the peak of production, and again after discard declines in 2010. We estimate that North Sea discards declined by 48% from 509,840 tonnes in 1990 to 267,549 tonnes in 2010. This waste had the potential to support 5.66 (95% credible intervals: 3.33–9.74) million seabirds in the 1990s, declining by 39% to 3.45 (1.98–5.78) million birds by 2010. Our study reveals the potential for fishery discards to support very large scavenging seabird communities but also shows how this has declined over recent decades. Discard bans, like the European Union's Landing Obligation, may reduce inflated scavenger communities, but come against a backdrop of gradual declines potentially buffering deleterious impacts. More work is required to reduce uncertainty and to generate global estimates, but our study highlights the magnitude of scavenger communities potentially supported by discards and thus the importance of understanding the wider ecological consequences of dumping fisheries waste.
Abstract.
Full text.
Sherley RB, Crawford RJM, de Blocq AD, Dyer BM, Geldenhuys D, Hagen C, Kemper J, Makhado AB, Pichegru L, Tom D, et al (2020). The conservation status and population decline of the African penguin deconstructed in space and time.
Ecology and Evolution,
10(15).
Abstract:
The conservation status and population decline of the African penguin deconstructed in space and time
Understanding changes in abundance is crucial for conservation, but population growth rates often vary over space and time. We use 40 years of count data (1979–2019) and Bayesian state-space models to assess the African penguin Spheniscus demersus population under IUCN Red List Criterion A. We deconstruct the overall decline in time and space to identify where urgent conservation action is needed. The global African penguin population met the threshold for Endangered with a high probability (97%), having declined by almost 65% since 1989. An historical low of ~17,700 pairs bred in 2019. Annual changes were faster in the South African population (−4.2%, highest posterior density interval, HPDI: −7.8 to −0.6%) than the Namibian one (−0.3%, HPDI: −3.3 to +2.6%), and since 1999 were almost −10% at South African colonies north of Cape Town. Over the 40-year period, the Eastern Cape colonies went from holding ~25% of the total penguin population to ~40% as numbers decreased more rapidly elsewhere. These changes coincided with an altered abundance and availability of the main prey of African penguins. Our results underline the dynamic nature of population declines in space as well as time and highlight which penguin colonies require urgent conservation attention.
Abstract.
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Lane JV, Jeavons R, Deakin Z, Sherley RB, Pollock CJ, Wanless RJ, Hamer KC (2020). Vulnerability of northern gannets to offshore wind farms; seasonal and sex-specific collision risk and demographic consequences. Marine Environmental Research, 162, 105196-105196.
2019
Sherley RB, Winker H, Rigby CL, Kyne PM, Pollom R, Pacoureau N, Herman K, Carlson JK, Yin JS, Kindsvater HK, et al (2019). Estimating IUCN Red List population reduction: JARA—A decision‐support tool applied to pelagic sharks.
Conservation Letters,
13(2).
Full text.
Crawford RJM, Sydeman WJ, Thompson SA, Sherley R, Makhado AB (2019). Food habits of an endangered seabird indicate recent poor forage fish availability. ICES Journal of Marine Science, 76, 1344-1352.
Dyer BM, Cooper J, Crawford RJM, Sherley RB, Somhlaba S, Cockcroft A, Upfold L, Makhado AB (2019). Geographical and temporal variation in the diet of Bank Cormorants Phalacrocorax neglectus in South Africa.
Ostrich,
90(4), 373-390.
Abstract:
Geographical and temporal variation in the diet of Bank Cormorants Phalacrocorax neglectus in South Africa
© 2019, © 2019 NISC (Pty) Ltd. The Bank Cormorant Phalacrocorax neglectus is endemic to the Benguela upwelling ecosystem off southwest Africa and is classified as Endangered owing to a recent large reduction in its number. It is thought that food scarcity, including a decreased abundance of West Coast rock lobster Jasus lalandii, has been a major driver of the decrease, yet its diet in South Africa is poorly known. We collected 941 pellets regurgitated by Bank Cormorants, at 18 South African breeding colonies during 1975–1985, and 1 523 pellets at 17 colonies during 1995–2002. The species composition of the diet (% numbers) was significantly different between the two periods, with widespread decreases in proportions of rock lobster in the west and of octopus and cuttlefish Sepia spp. at most localities. These taxa were replaced in the diet by fish, including Gobiidae and Clinidae. The pelagic goby Sufflogobius bibarbatus, an important prey of Bank Cormorants in Namibia, was absent from pellets collected in 1975–1985 but common at northern localities from 1995–2002. Composition of the diet by frequency of occurrence was only determined for 1995–2002, when rock lobster was present in 67% of all samples collected, cuttlefish in 39%, and Clinidae in 32%. Data for 1975–1985 and 1995–2002 showed that carapace lengths of rock lobsters eaten by Bank Cormorants averaged 56 mm (range 22–82 mm) and 50 mm (range 22–75 mm), respectively, which compares to the minimum legal size of 75 mm for fisheries in South Africa. This energy- rich prey item was an important constituent of the diet in the winter breeding period.
Abstract.
Ropert-Coudert Y, Chiaradia A, Ainley D, Barbosa A, Boersma PD, Brasso R, Dewar M, Ellenberg U, Garcia-Borboroglu P, Emmerson L, et al (2019). Happy Feet in a Hostile World? the Future of Penguins Depends on Proactive Management of Current and Expected Threats.
FRONTIERS IN MARINE SCIENCE,
6 Author URL.
Ropert-Coudert Y, Chiaradia A, Ainley D, Barbosa A, Boersma PD, Brasso R, Dewar M, Ellenberg U, García-Borboroglu P, Emmerson L, et al (2019). Happy feet in a hostile world? the future of penguins depends on proactive management of current and expected threats.
Frontiers in Marine Science,
6(May).
Abstract:
Happy feet in a hostile world? the future of penguins depends on proactive management of current and expected threats
© 2019 Ropert-Coudert, Chiaradia, Ainley, Barbosa, Boersma, Brasso, Dewar, Ellenberg, García-Borboroglu, Emmerson, Hickcox, Jenouvrier, Kato, McIntosh, Lewis, Ramírez, Ruoppolo, Ryan, Seddon, Sherley, Vanstreels, Waller, Woehler and Trathan. Penguins face a wide range of threats. Most observed population changes have been negative and have happened over the last 60 years. Today, populations of 11 penguin species are decreasing. Here we present a review that synthesizes details of threats faced by the world's 18 species of penguins. We discuss alterations to their environment at both breeding sites on land and at sea where they forage. The major drivers of change appear to be climate, and food web alterations by marine fisheries. In addition, we also consider other critical and/or emerging threats, namely human disturbance near nesting sites, pollution due to oil, plastics and chemicals such as mercury and persistent organic compounds. Finally, we assess the importance of emerging pathogens and diseases on the health of penguins. We suggest that in the context of climate change, habitat degradation, introduced exotic species and resource competition with fisheries, successful conservation outcomes will require new and unprecedented levels of science and advocacy. Successful conservation stories of penguin species across their geographical range have occurred where there has been concerted effort across local, national and international boundaries to implement effective conservation planning.
Abstract.
Winker H, Sherley R (2019). JARA: 'Just Another Red-List Assessment'.
bioRxiv, 672899-672899.
Abstract:
JARA: 'Just Another Red-List Assessment'
Identifying species at risk of extinction is necessary to prioritise conservation efforts. The International Union for Conservation of Nature's (IUCN) Red List of Threatened Species is the global standard for quantifying extinction risk, with many species categorised on the basis of a reduction in population size. We introduce the Bayesian state-space framework 'JARA' (Just Another Red-List Assessment). Designed as decision-support tool, JARA allows both process error and uncertainty to be incorporated into IUCN Red List assessments under criterion A. JARA outputs easy to interpret graphics showing the posterior probability of the population decline displayed against the IUCN Red List categories, and assigns each category an associated probability given process and observation uncertainty. JARA is designed to be easy to use, rapid and widely applicable, so conservation practitioners can apply it to their own count or relative abundance data. We illustrate JARA using three real-world examples: (1) relative abundance indices for two elasmobranchs, Yellowspotted Skate Leucoraja wallacei and Whitespot Smoothhound Mustelus palumbes; (2) a comparison of standardized abundance indices for Atlantic Blue Marlin Makaira nigricans and (3) absolute abundance data for Cape Gannets Morus capensis. Finally, using a simulation experiment, we demonstrate how JARA provides greater accuracy than two approaches commonly used to assigning a Red List Status under criterion A. Tools like JARA can help further standardise Red List evaluations, increasing objectivity and lowering the risk of misclassification. The consequences for global conservation efforts could be substantial.
Abstract.
Campbell KJ, Steinfurth A, Underhill LG, Coetzee JC, Dyer BM, Ludynia K, Makhado AB, Merkle D, Rademan J, Upfold L, et al (2019). Local forage fish abundance influences foraging effort and offspring condition in an endangered marine predator.
Journal of Applied Ecology,
56(7), 1751-1760.
Full text.
Deakin Z, Hamer KC, Sherley RB, Bearhop S, Bodey TW, Clark BL, James Grecian W, Gummery M, Lane J, Morgan G, et al (2019). Sex differences in migration and demography of a wide-ranging seabird, the Northern Gannet.
Marine Ecology Progress Series,
622, 191-201.
Abstract:
Sex differences in migration and demography of a wide-ranging seabird, the Northern Gannet
© the authors 2019. Marine vertebrates show a diversity of migration strategies, including sex differences. This may lead to differential demography, but the consequences of such between-sex variation are little understood. Here, we studied the migration of known-sex northern gannets Morus bassanus — a partial migrant with females ~8 % heavier than males. We used geolocators to determine wintering areas of 49 breeding adults (19 females and 30 males during 2010 to 2014) from 2 colonies in the northeast Atlantic (Bass Rock and Grassholm, UK). We also tested for sex-specific survival probabilities using capture−mark−recapture methods (n = 72 individuals Bass Rock, n = 229 individuals Grassholm; 2010−2018) and applied sex-specific population projection matrices (PPMs) to quantify population-level effects. Tracked gannets wintered in a range of large marine ecosystems (LMEs): Canary Current LME (CCLME; 69 %), Celtic-Biscay Shelf LME (16 %), Iberian Coastal LME (8 %), North Sea LME (4 %) or Mediterranean LME (2 %). Migratory destination differed between the sexes: 90 % of females vs. 57 % of males wintered in the CCLME. Survival was similar between the sexes at Bass Rock (mean ± 95 % CI = 0.951 ± 0.053 and 0.956 ± 0.047 for females and males, respectively). At Grassholm, there was evidence of slight sex differences in breeder survival: females had lower annual survival (0.882 ± 0.040) than males (0.946 ± 0.026). At Bass Rock, PPMs with no sex effect best fitted the observed population increase (1994−2014). Sex-specific PPMs fitted the population estimates for Grassholm (1995−2015). Our results reveal that female gannets are more likely to travel further than males to winter in the CCLME. This difference is unlikely due to morphological differences, unlike in other bird species. However, the reason for slightly higher over-winter female mortality at Grassholm is unclear.
Abstract.
Gianuca D, Votier SC, Pardo D, Wood AG, Sherley RB, Ireland L, Choquet R, Pradel R, Townley S, Forcada J, et al (2019). Sex‐specific effects of fisheries and climate on the demography of sexually dimorphic seabirds. Journal of Animal Ecology, 88(9), 1366-1378.
Sherley RB, Crawford RJM, Dyer BM, Kemper J, Makhado AB, Masotla M, Pichegru L, Pistorius PA, Roux JP, Ryan PG, et al (2019). The status and conservation of the Cape Gannet Morus capensis.
Ostrich,
90(4), 335-346.
Abstract:
The status and conservation of the Cape Gannet Morus capensis
© 2019, © 2019 NISC (Pty) Ltd. The Cape Gannet Morus capensis is one of several seabird species endemic to the Benguela upwelling ecosystem (BUS) but whose population has recently decreased, leading to an unfavourable IUCN Red List assessment. Application of ‘JARA’ (‘Just Another Red-List Assessment,’ a Bayesian state-space tool used for IUCN Red List assessments) to updated information on the areas occupied by Cape Gannets and the nest densities of breeding birds at their six colonies, suggested that the species should be classified as Vulnerable. However, the rate of decrease of Cape Gannets in their most-recent generation exceeded that of the previous generation, primarily as a result of large decreases at Bird Island, Lambert’s Bay, and Malgas Island, off South Africa’s west coast (the western part of their range). Since the 1960s, there has been an ongoing redistribution of the species from northwest to southeast around southern Africa, and ∼70% of the population now occurs on the south coast of South Africa, at Bird Island in Algoa Bay, on the eastern border of the BUS. Recruitment rather than adult survival may be limiting the present population; however, information on the seabird’s demographic parameters and mortality in fisheries is lacking for colonies in the northern part of the BUS. Presently, major threats to Cape Gannet include: substantially decreased availability of their preferred prey in the west; heavy mortalities of eggs, chicks and fledglings at and around colonies, inflicted by Cape Fur Seals Arctocephalus pusillus and other seabirds; substantial disturbance at colonies caused by Cape Fur Seals attacking adult gannets ashore; oiling; and disease.
Abstract.
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2018
Gaglio D, Sherley RB, Ryan PG, Cook TR (2018). A non-invasive approach to estimate the energetic requirements of an increasing seabird population in a perturbed marine ecosystem.
Scientific Reports,
8(1).
Full text.
Sherley RB, Barham BJ, Barham PJ, Campbell KJ, Crawford RJM, Grigg J, Horswill C, McInnes A, Morris TL, Pichegru L, et al (2018). Bayesian inference reveals positive but subtle effects of experimental fishery closures on marine predator demographics.
Proceedings of the Royal Society B: Biological Sciences,
285(1871), 20172443-20172443.
Abstract:
Bayesian inference reveals positive but subtle effects of experimental fishery closures on marine predator demographics
. Global forage-fish landings are increasing, with potentially grave consequences for marine ecosystems. Predators of forage fish may be influenced by this harvest, but the nature of these effects is contentious. Experimental fishery manipulations offer the best solution to quantify population-level impacts, but are rare. We used Bayesian inference to examine changes in chick survival, body condition and population growth rate of endangered African penguins
. Spheniscus demersus
. in response to 8 years of alternating time–area closures around two pairs of colonies. Our results demonstrate that fishing closures improved chick survival and condition, after controlling for changing prey availability. However, this effect was inconsistent across sites and years, highlighting the difficultly of assessing management interventions in marine ecosystems. Nevertheless, modelled increases in population growth rates exceeded 1% at one colony; i.e. the threshold considered biologically meaningful by fisheries management in South Africa. Fishing closures evidently can improve the population trend of a forage-fish-dependent predator—we therefore recommend they continue in South Africa and support their application elsewhere. However, detecting demographic gains for mobile marine predators from small no-take zones requires experimental time frames and scales that will often exceed those desired by decision makers.
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Abstract.
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Gaglio D, Cook TR, McInnes A, Sherley RB, Ryan PG (2018). Foraging plasticity in seabirds: a non-invasive study of the diet of greater crested terns breeding in the Benguela region.
PLoS ONE,
13(1).
Abstract:
Foraging plasticity in seabirds: a non-invasive study of the diet of greater crested terns breeding in the Benguela region
© 2018 Gaglio et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Marine predators, such as seabirds, are useful indicators of marine ecosystem functioning. In particular, seabird diet may reflect variability in food-web composition due to natural or human-induced environmental change. Diet monitoring programmes, which sample diet non-invasively, are valuable aids to conservation and management decision-making. We investigated the diet of an increasing population of greater crested terns Thalasseus bergii in the Western Cape, South Africa, during three successive breeding seasons (2013 to 2015), when populations of other seabirds feeding on small pelagic schooling fish in the region were decreasing. Breeding greater crested terns carry prey in their bills, so we used an intensive photo-sampling method to record their diet with little disturbance. We identified 24,607 prey items from at least 47 different families, with 34 new prey species recorded. Fish dominated the diet, constituting 94% of prey by number, followed by cephalopods (3%), crustaceans (2%) and insects (1%). The terns mainly targeted surface-schooling Clupeiformes, with anchovy Engraulis encrasicolus the most abundant prey in all three breeding seasons (65% overall). Prey composition differed significantly between breeding stages and years, with anchovy most abundant at the start of the breeding season, becoming less frequent as the season progressed. The proportion of anchovy in the diet also was influenced by environmental factors; anchovy occurred more frequently with increasing wind speeds and was scarce on foggy days, presumably because terns rely in part on social facilitation to locate anchovy schools. The application of this intensive and non-invasive photo-sampling method revealed an important degree of foraging plasticity for this seabird within a context of locally reduced food availability, suggesting that, unlike species that specialise on a few high-quality prey, opportunistic seabirds may be better able to cope with reductions in the abundance of their preferred prey.
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Gaglio D, Cook TR, Sherley RB, Ryan PG (2018). How many can you catch? Factors influencing the occurrence of multi-prey loading in provisioning Greater Crested Terns.
Ostrich,
89(2), 145-149.
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Provencher JF, Borrelle S, Sherley RB, Avery-Gomm S, Hodum P, Bond A, Major HL, McCoy KD, Crawford R, Merkel F, et al (2018). Seabirds. In (Ed)
World Seas: an Environmental Evaluation Volume III: Ecological Issues and Environmental Impacts, 133-162.
Abstract:
Seabirds
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Payo-Payo A, Sanz-Aguilar A, Gaglio D, Sherley RB, Cook TR, Altwegg R, Ryan PG (2018). Survival estimates for the greater crested tern Thalasseus bergii in southern Africa.
African Journal of Marine Science,
40(1), 43-50.
Abstract:
Survival estimates for the greater crested tern Thalasseus bergii in southern Africa
© 2018 NISC (Pty) Ltd. The nominate race of the greater crested tern Thalasseus bergii breeds only along the coast of the Benguela region (west coast) of southern Africa, where its population is increasing, in contrast to other species of breeding seabirds in the region which similarly depend on forage fish. Although this population’s trends are well known, its demographic parameters remain obscure. We used multi-event capture–recapture–recovery modelling to provide the first estimates of survival. The survival rate of birds older than two years was 0.93 (0.91–0.95); second-year survival was 0.93 (0.90–0.95) and first-year survival was 0.80 (0.73–0.85). A resighting of a 34-year-old bird is a new longevity record for the species. Population growth rates projected with a Leslie matrix model that included our survival estimates were very similar to estimates from annual counts of the breeding population (7–8% y−1), suggesting that these survival estimates adequately describe the species’ demography. High survival rates have likely contributed to the species’ recent population increase in the region.
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Gaglio D, Sherley RB, Cook TR, Ryan PG, Flower T (2018). The costs of kleptoparasitism: a study of mixed-species seabird breeding colonies.
Behavioral Ecology,
29(4), 939-947.
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2017
Sydeman WJ, Thompson SA, Anker-Nilssen T, Arimitsu M, Bennison A, Bertrand S, Boersch-Supan P, Boyd C, Bransome NC, Crawford RJM, et al (2017). Best practices for assessing forage fish fisheries-seabird resource competition.
Fisheries Research,
194, 209-221.
Abstract:
Best practices for assessing forage fish fisheries-seabird resource competition
© 2017 Elsevier B.V. Worldwide, in recent years capture fisheries targeting lower-trophic level forage fish and euphausiid crustaceans have been substantial (∼20 million metric tons [MT] annually). Landings of forage species are projected to increase in the future, and this harvest may affect marine ecosystems and predator-prey interactions by removal or redistribution of biomass central to pelagic food webs. In particular, fisheries targeting forage fish and euphausiids may be in competition with seabirds, likely the most sensitive of marine vertebrates given limitations in their foraging abilities (ambit and gape size) and high metabolic rate, for food resources. Lately, apparent competition between fisheries and seabirds has led to numerous high-profile conflicts over interpretations, as well as the approaches that could and should be used to assess the magnitude and consequences of fisheries-seabird resource competition. In this paper, we review the methods used to date to study fisheries competition with seabirds, and present “best practices” for future resource competition assessments. Documenting current fisheries competition with seabirds generally involves addressing two major issues: 1) are fisheries causing localized prey depletion that is sufficient to affect the birds? (i.e. are fisheries limiting food resources?), and 2) how are fisheries-induced changes to forage stocks affecting seabird populations given the associated functional or numerical response relationships? Previous studies have been hampered by mismatches in the scale of fisheries, fish, and seabird data, and a lack of causal understanding due to confounding by climatic and other ecosystem factors (e.g. removal of predatory fish). Best practices for fisheries-seabird competition research should include i) clear articulation of hypotheses, ii) data collection (or summation) of fisheries, fish, and seabirds on matched spatio-temporal scales, and iii) integration of observational and experimental (including numerical simulation) approaches to establish connections and causality between fisheries and seabirds. As no single technique can provide all the answers to this vexing issue, an integrated approach is most promising to obtain robust scientific results and in turn the sustainability of forage fish fisheries from an ecosystem perspective.
Abstract.
Morten JM, Parsons NJ, Schwitzer C, Holderied MW, Sherley RB (2017). Body condition as a quantitative tool to guide hand-rearing decisions in an endangered seabird.
Animal Conservation,
20(5), 471-479.
Abstract:
Body condition as a quantitative tool to guide hand-rearing decisions in an endangered seabird
© 2017 the Zoological Society of London the use of wildlife rehabilitation for conservation is growing, but quantitative criteria are rarely used to guide whether and when to remove animals from the wild. Since 2006, large numbers of African penguin Spheniscus demersus chicks have been abandoned annually when adults enter moult with dependent young still in the nest. As part of conservation initiatives for this endangered species, these chicks were collected and hand reared to fledging age. Post-release survival has been well documented; in this study we develop models to predict survival of individuals during rehabilitation with the aim of improving hand-rearing success and guiding the use of scarce resources. For 1455 chicks abandoned between 2008 and 2013, we assessed whether a chick body condition index (BCI) could predict outcome (death or release) and time spent in rearing. In addition, for a subset of 173 chicks in 2012, we assessed whether BCI at admission influenced chick growth rates during rehabilitation and examined whether the use of additional structural measurements and sex provided additional power to predict outcome. Models predicted an 82.9% (95% confidence interval: 73.3–89.5%) release rate for chicks admitted with a BCI >0, the proposed guideline for removal from colonies. This fell below 50% for BCIs
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Sherley RB, Botha P, Underhill LG, Ryan PG, van Zyl D, Cockcroft AC, Crawford RJM, Dyer BM, Cook TR (2017). Defining ecologically relevant scales for spatial protection with long-term data on an endangered seabird and local prey availability.
Conservation Biology,
31(6), 1312-1321.
Abstract:
Defining ecologically relevant scales for spatial protection with long-term data on an endangered seabird and local prey availability
© 2017 Society for Conservation Biology Human activities are important drivers of marine ecosystem functioning. However, separating the synergistic effects of fishing and environmental variability on the prey base of nontarget predators is difficult, often because prey availability estimates on appropriate scales are lacking. Understanding how prey abundance at different spatial scales links to population change can help integrate the needs of nontarget predators into fisheries management by defining ecologically relevant areas for spatial protection. We investigated the local population response (number of breeders) of the Bank Cormorant (Phalacrocorax neglectus), a range-restricted endangered seabird, to the availability of its prey, the heavily fished west coast rock lobster (Jasus lalandii). Using Bayesian state-space modeled cormorant counts at 3 colonies, 22 years of fisheries-independent data on local lobster abundance, and generalized additive modeling, we determined the spatial scale pertinent to these relationships in areas with different lobster availability. Cormorant numbers responded positively to lobster availability in the regions with intermediate and high abundance but not where regime shifts and fishing pressure had depleted lobster stocks. The relationships were strongest when lobsters 20–30 km offshore of the colony were considered, a distance greater than the Bank Cormorant's foraging range when breeding, and may have been influenced by prey availability for nonbreeding birds, prey switching, or prey ecology. Our results highlight the importance of considering the scale of ecological relationships in marine spatial planning and suggest that designing spatial protection around focal species can benefit marine predators across their full life cycle. We propose the precautionary implementation of small-scale marine protected areas, followed by robust assessment and adaptive-management, to confirm population-level benefits for the cormorants, their prey, and the wider ecosystem, without negative impacts on local fisheries.
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Gaglio D, Cook TR, Connan M, Ryan PG, Sherley RB (2017). Dietary studies in birds: testing a non-invasive method using digital photography in seabirds.
Methods in Ecology and Evolution,
8(2), 214-222.
Abstract:
Dietary studies in birds: testing a non-invasive method using digital photography in seabirds
© 2016 the Authors. Methods in Ecology and Evolution © 2016 British Ecological Society Dietary studies give vital insights into foraging behaviour, with implications for understanding changing environmental conditions and the anthropogenic impacts on natural resources. Traditional diet sampling methods may be invasive or subject to biases, so developing non-invasive and unbiased methods applicable to a diversity of species is essential. We used digital photography to investigate the diet fed to chicks of a prey-carrying seabird and compared our approach (photo-sampling) to a traditional method (regurgitations) for the greater crested tern Thalasseus bergii. Over three breeding seasons, we identified >24 000 prey items of at least 48 different species, more than doubling the known diversity of prey taken by this population of terns. We present a method to estimate the length of the main prey species (anchovy Engraulis encrasicolus) from photographs, with an accuracy
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Gaglio D, Sherley R, Cook T (2017). Insects in the diet of the Greater Crested Tern Thalasseus bergii bergii in Southern Africa. Marine Ornithology, 43, 131-132.
Sherley RB, Ludynia K, Dyer BM, Lamont T, Makhado AB, Roux J-P, Scales KL, Underhill LG, Votier SC (2017). Metapopulation Tracking Juvenile Penguins Reveals an Ecosystem-wide Ecological Trap.
Current Biology,
27(4), 563-568.
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Sherley RB (2017). PhD jobs: Revamp funding structures.
Nature,
551(7681).
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Brisson-Curadeau É, Bird D, Burke C, Fifield DA, Pace P, Sherley RB, Elliott KH (2017). Seabird species vary in behavioural response to drone census.
Scientific Reports,
7(1).
Abstract:
Seabird species vary in behavioural response to drone census
© 2017 the Author(s). Unmanned aerial vehicles (UAVs) provide an opportunity to rapidly census wildlife in remote areas while removing some of the hazards. However, wildlife may respond negatively to the UAVs, thereby skewing counts. We surveyed four species of Arctic cliff-nesting seabirds (glaucous gull Larus hyperboreus, Iceland gull Larus glaucoides, common murre Uria aalge and thick-billed murre Uria lomvia) using a UAV and compared censusing techniques to ground photography. An average of 8.5% of murres flew off in response to the UAV, but >99% of those birds were non-breeders. We were unable to detect any impact of the UAV on breeding success of murres, except at a site where aerial predators were abundant and several birds lost their eggs to predators following UAV flights. Furthermore, we found little evidence for habituation by murres to the UAV. Most gulls flew off in response to the UAV, but returned to the nest within five minutes. Counts of gull nests and adults were similar between UAV and ground photography, however the UAV detected up to 52.4% more chicks because chicks were camouflaged and invisible to ground observers. UAVs provide a less hazardous and potentially more accurate method for surveying wildlife. We provide some simple recommendations for their use.
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Votier SC, Sherley RB (2017). Seabirds. Current Biology, 27(11), R448-R450.
Crawford R, Ellenberg U, Frere E, Hagen C, Baird K, Brewin P, Crofts S, Glass J, Mattern T, Pompert J, et al (2017). Tangled and drowned: a global review of penguin bycatch in fisheries. Endangered Species Research, 34, 373-396.
2016
Sherley RB, Barham BJ, Barham PJ, Leshoro TM, Underhill LG (2016). Artificial nests enhance the breeding productivity of African Penguins (Spheniscus demersus) on Robben Island, South Africa. Emu - Austral Ornithology, 112(2), 97-106.
Weller F, Sherley RB, Shannon LJ, Jarre A, Stewart T, Scott L, Altwegg R, Cecchini LA, Crawford RJM, Geldenhuys D, et al (2016). Penguins' perilous conservation status calls for complementary approach based on sound ecological principles: reply to Butterworth et al. (2015). Ecological Modelling, 337, 1-3.
Weller F, Sherley RB, Waller LJ, Ludynia K, Geldenhuys D, Shannon LJ, Jarre A (2016). System dynamics modelling of the Endangered African penguin populations on Dyer and Robben islands, South Africa.
Ecological Modelling,
327, 44-56.
Abstract:
System dynamics modelling of the Endangered African penguin populations on Dyer and Robben islands, South Africa
© 2016 Elsevier B.V. African penguins (Spheniscus demersus) in South Africa have been subject to rapid decline in the 20th century and are currently listed as "endangered" on the IUCN Red List. A stochastic, stage-specific system dynamics model with spatial components was developed to investigate the interaction of multiple pressures on penguin population development, and originally applied to study conservation management options for the penguin colony at Robben Island, Table Bay, South Africa. We here present an extension of the model to the nearby colony at Dyer Island. The modelled population was found to be strongly dominated by the effects of Cape fur seal (Arctocephalus pusillus pusillus) predation and immature emigration, which appear to be key drivers behind current declines in population numbers at this colony. Chronic low-level oiling also had a consistent impact despite ongoing mitigation measures, while kelp gull predation had a lower effect than expected. At current low population size, the pressure from either seal predation or immature emigration seems sufficient to mask any beneficial effects to penguins from possible improvements in available food biomass (e.g. from fishery restrictions). Results suggest that conservation management at this colony should focus on regular culling of predating seals combined with improving availability of prey (thus discouraging emigration) both in the foraging range of breeding penguins and in their general foraging area. Our findings demonstrate the use of site-specific scenario tools to explore conservation strategies in data-poor management situations.
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2015
Sherley RB, Winker H, Altwegg R, van der Lingen CD, Votier SC, Crawford RJM (2015). Bottom-up effects of a no-take zone on endangered penguin demographics.
Biology Letters,
11(7), 20150237-20150237.
Abstract:
Bottom-up effects of a no-take zone on endangered penguin demographics
. Marine no-take zones can have positive impacts for target species and are increasingly important management tools. However, whether they indirectly benefit higher order predators remains unclear. The endangered African penguin (
. Spheniscus demersus
. ) depends on commercially exploited forage fish. We examined how chick survival responded to an experimental 3-year fishery closure around Robben Island, South Africa, controlling for variation in prey biomass and fishery catches. Chick survival increased by 18% when the closure was initiated, which alone led to a predicted 27% higher population compared with continued fishing. However, the modelled population continued to decline, probably because of high adult mortality linked to poor prey availability over larger spatial scales. Our results illustrate that small no-take zones can have bottom-up benefits for highly mobile marine predators, but are only one component of holistic, ecosystem-based management regimes.
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Gaglio D, Cook TR, Sherley RB (2015). Egg morphology of Swift Terns in South Africa. Ostrich, 86(3), 287-289.
2014
Weller F, Cecchini L-A, Shannon L, Sherley RB, Crawford RJM, Altwegg R, Scott L, Stewart T, Jarre A (2014). A system dynamics approach to modelling multiple drivers of the African penguin population on Robben Island, South Africa. Ecological Modelling, 277, 38-56.
Sherley RB, Abadi F, Ludynia K, Barham BJ, Clark AE, Altwegg R (2014). Age-specific survival and movement among major African PenguinSpheniscus demersuscolonies. Ibis, 156(4), 716-728.
Sherley RB, Waller LJ, Strauss V, Geldenhuys D, Underhill LG, Parsons NJ (2014). Hand-Rearing, Release and Survival of African Penguin Chicks Abandoned Before Independence by Moulting Parents. PLoS ONE, 9(10), e110794-e110794.
Ludynia K, Waller LJ, Sherley RB, Abadi F, Galada Y, Geldenhuys D, Crawford RJM, Shannon LJ, Jarre A (2014). Processes influencing the population dynamics and conservation of African penguins on Dyer Island, South Africa. African Journal of Marine Science, 36(2), 253-267.
2013
Sherley RB, Barham PJ, Barham BJ, Crawford RJM, Dyer BM, Leshoro TM, Makhado AB, Upfold L, Underhill LG (2013). Growth and decline of a penguin colony and the influence on nesting density and reproductive success. Population Ecology, 56(1), 119-128.
Sherley RB, Underhill LG, Barham BJ, Barham PJ, Coetzee JC, Crawford RJM, Dyer BM, Leshoro TM, Upfold L (2013). Influence of local and regional prey availability on breeding performance of African penguins Spheniscus demersus. Marine Ecology Progress Series, 473, 291-301.
Bonato M, Evans MR, Hasselquist D, Sherley RB, Cloete SWP, Cherry MI (2013). Ostrich chick humoral immune responses and growth rate are predicted by parental immune responses and paternal colouration. Behavioral Ecology and Sociobiology, 67(12), 1891-1901.
Sherley RB, Ludynia K, Lamont T, Roux JP, Crawford RJM, Underhill LG (2013). The initial journey of an Endangered penguin: implications for seabird conservation. Endangered Species Research, 21(1), 89-95.
2011
Sherley RB, Ludynia K, Underhill LG, Jones R, Kemper J (2011). Storms and heat limit the nest success of Bank Cormorants: implications of future climate change for a surface-nesting seabird in southern Africa. Journal of Ornithology, 153(2), 441-455.
2010
Villiers MSD, Mecenero S, Sherley RB, Heinze E, Kieser J, Leshoro TM, Merbold L, Nordt A, Parsons NJ, Peter H-U, et al (2010). Introduced European Rabbits (Oryctolagus cuniculus) and Domestic Cats (Felis catus) on Robben Island: Population Trends and Management Recommendations. South African Journal of Wildlife Research, 40(2), 139-148.
Sherley RB, Burghardt T, Barham PJ, Campbell N, Cuthill IC (2010). Spotting the difference: towards fully-automated population monitoring of African penguins Spheniscus demersus. Endangered Species Research, 11, 101-111.
2009
Underhill LG, Sherley RB, Dyer BM, Crawford RJM (2009). Interactions between snakes and seabirds on Robben, Schaapen and Meeuw Islands, Western Cape province, South Africa.
OSTRICH,
80(2), 115-118.
Author URL.