A team of marine biologists from Trinity College Dublin, Queen’s University Belfast (QUB) and Fjordstrong have filmed a giant sixgill shark swimming in Irish coastal waters — in what is a European first.
These large, prehistoric-looking sharks typically inhabit deep, dark waters off the continental shelf (at depths of 200-2,500metres). However, there are a few special sites discovered off County Clare, by local charter skipper, Luke Aston, where these apex predators can be found in relatively shallow water (50-60m).
The team of scientists set out last week to learn more about this unusual shark population. Led by Haley Dolton, PhD candidate in Trinity’s School of Natural Sciences, the team deployed modified ABUVs (Auto-Release Baited Underwater Video — a patented fish-identifying video recorder) developed by Belfast-based marine survey company, Fjordstrong.
They grabbed footage of a four-metre sixgill shark casually cruising past their lens several times. The encounter occurred after the team had seen numerous more common fish species, leading one of the researchers to shout: “That’s not another dogfish!”
Haley Dolton said: “Sixgill sharks are an incredible species and this particular site off the Irish coastline is of particular interest as large, females have regularly been sighted in shallow waters. For some reason this area is important to them and, given that all sixgills caught by Luke Aston appear to be females, there is a suggestion that this area is important for reproductive purposes. Getting the chance to try and solve this riddle in sixgill shark biology is a very intriguing part of my PhD and could have major implications for conservation of this species.”
Sixgills are 'named for what you see' — they have six gill slits whereas most other sharks only have five.
While they may be visiting the Clare coast to use the shallower water as a 'shark nursery' or safe zone, there isn't a danger of Ireland's Wild Atlantic Way becoming the next Amity though. As Ms Dolton explains, these sixgill sharks are more like 'scavengers' which feed on the carcasses of mammals. "Research has found blubber in the stomachs of some of these sharks so they may be eating something like dolphins or seals which have died and are at the bottom of the sea."
This sighting kicked off a series of studies by this all-Ireland team to understand why the south-west coast of Ireland is such a hotspot for elasmobranchs (sharks and rays). They will expand their ocean exploration of this area over the next 18 months.
Ireland has the richest elasmobranch diversity in Europe, with giants such as the basking sharks and sixgills regularly cruising by. It is also one of the last refugia on earth for the critically endangered flapper skate (the largest skate on earth).
These factors are reflected by the increasing attractiveness of Ireland as a destination for shark biologists (Haley’s supervisor Dr Nick Payne recently moved here from Australia where he worked with great whites and tiger sharks).
Dr Nick Payne, Assistant Professor in Trinity’s School of Natural Sciences, said: “It’s like an aquatic Jurassic Park out there! Ireland is the gateway to the Atlantic and we are increasingly amazed at how important Irish waters seem to be for these huge shark and ray species. It means we in Ireland have a responsibility to look after them.”
Dr Patrick Collins, lecturer at Queens University Belfast, added: “We are going to need a bigger boat… to come back here next year and collect more data — we have only just scratched below the surface.”