Glowing deep-water sharks’ DNA reveals distinct populations

deep sea lanternshark
The black regions on the velvet belly lanternshark are covered in light emitting organs called photophores. Credit: Chris BirdShark Devocean.

An international collaboration, led by the University of Exeter and the University of Salford, has been investigating the population structure of the deep sea velvet belly lanternshark (Etmopterus spinax), known for its luminous blue glow, in an effort to protect them from fisheries bycatch.

This shark 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 deep-water species to get caught up in the nets.

Previous research showed high connectivity and lack of population structure in members of deep-water sharks across large oceanic distances. In the current study, teams from the UK, Greece, Ireland, Norway, Italy and Portugal joined forces to discover distinct differences in population structure between lantern sharks found in the Mediterranean and those found in the northeast 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”.

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.

Catches of the velvet belly lanternshark have fallen by 80% since the 70’s, due to an increase in fisheries bycatch in some regions. Many deep sea sharks are even more vulnerable to over fishing because they grow and reproduce so slowly. We really need to understand more about the biology of these beautiful fish in order to protect them.

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.

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Co-authors: Will Davidson, Dr Andrew M. Griffiths and Dr Chrysoula Gubili
Citation: Gubili C, Macleod K, Perry W, Hanel P, Batzakas I, Farrell ED, Lynghammar A, Mancusi C, Mariani S, Menezes GM, Neat F, Scarcella G, Griffiths AM. (2016). Connectivity in the Deep: Phylogeography of the Velvet Belly Lanternshark. Deep Sea Research I, 115:233-239. doi: