Lanternsharks. © Christopher Bird
Shining a light in the dark: Glowing sharks DNA reveals distinct populations
An international team, led by Dr Andrew Griffiths at the University of Exeter, has been investigating the population structure of the deep sea velvet belly lanternshark, known for its luminous blue glow, in an effort to protect them from fisheries bycatch.
The collaboration between teams in the UK, Greece, Ireland, Norway, Italy and Portugal found distinct differences in population structure between lantern sharks found in the Mediterranean and those found in the Atlantic.
Dr Griffiths said “most previous work on other deep-sea sharks has not shown any evidence of population structure, meaning sharks across the whole Atlantic belong to one big population”. He goes on to say “This paper is amongst the first evidence to suggest there are barriers to movement and gene-flow, perhaps associated with shallow regions of the ocean”.
The velvet belly lanternshark is found in the deep sea where it wouldn’t normally be threatened by fishing. However, as fish stocks are decreasing, fishermen are trawling at greater and greater depths in order to maintain their catches. This in turn is causing ever more lanternsharks to get caught up in the nets.
Since the 1970s, numbers of the velvet belly lanternshark have fallen by as much as 80% due to fisheries bycatch in some regions. Dr Griffiths adds “Many species of deep sea sharks are even more vulnerable to over fishing than the lantern shark, because they reproduce so slowly. We really need to understand more about the biology of these beautiful fish in order to protect them”.
Using tissue from sharks caught throughout the northeast Atlantic and the Mediterranean, the team used DNA sequencing to map the population structure of these sharks. Their results found very little genetic difference within each of the two regions. However, when comparing the two, the DNA of those in the Mediterranean was different to those caught in the Atlantic suggesting that two distinct populations have formed. It is believed that the cause of this population split was sea levels falling after the last ice age, 100,000 years ago. The relatively shallow waters of the Strait of Gibraltar may have trapped the deep water sharks in the Mediterranean, separating the two groups and allowing them to diverge.
This has implications for how the sharks are fished and managed, as they could react differently to exploitation. It is hoped that the findings can be used to better manage European fisheries in an effort to minimise the ecological damage of bycatch.
The paper has been published in the journal Deep Sea Research 1;
Connectivity in the Deep: Phylogeography of the Velvet Belly Lanternshark
Written by Will Davidson, Biosciences Pressgang
Date: 28 July 2016