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Trinity Researchers Tag Basking Sharks in West Cork to Learn More About Ocean’s Second Largest Fish

13th May 2021
TCD researchers prepare to tag a basking shark under the water off the West Cork coast
Trinity researchers prepare to tag a basking shark off the West Cork coast Credit: TCD

Researchers from Trinity’s School of Natural Sciences were in West Cork earlier this month to tag some of the many basking sharks that have been frequenting our shores — and learn more about the second largest fish in the world’s oceans.

Funded by the Irish Research Council and Science Foundation Ireland, Assistant Professor Nicholas Payne and PhD candidate Haley Dolton spent a week on the water with West Cork Charters in which they managed to apply tags to four basking sharks.

These electronic tags will accumulate data about the sharks’ behaviour and physiology as they move around the coast feeding on plankton.

The goal, the researchers say, is to learn more about the anatomy and physiology of these gentle giants and hopefully guide conservation efforts for this endangered marine wildlife species.

“Basking sharks are a difficult species to study because they are not very abundant and they only grace our shores for a brief period each year, from April to August, so I am delighted we were able to learn so much about them this past week,” said Dr Payne.

Sadly the first phase of the pair’s work involved dissecting the remains of two basking sharks that washed up on the West Cork coast at the end of April, as previously reported on Afloat.ie.

“We would rather not have have had the opportunity to examine the two sharks that died prematurely before we took to the sea, but these sad events did at least help us learn more about them,” Dr Payne explained.

“Basking sharks are an endangered species and at risk of death from fishing bycatch and from getting struck by boats, so the more we know about them — especially their behaviour and physiology — the better chance we have of protecting them.

“The experience we had of observing live sharks in all their glory really emphasises that we should do our best to protect these incredible animals.”

Dolton added: “The amount of data we managed to collect throughout the whole week was phenomenal and beyond what I’d hoped for. We are currently analysing all the results and look forward to sharing our findings with everyone later in the year.”

Published in Sharks, Marine Science
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Sharks in Irish waters

Irish waters are home to 71 species of shark, skates and rays, 58 of which have been studied in detail and listed on the Ireland Red List of Cartilaginous fish. Irish sharks range from small Sleeper sharks, Dogfish and Catsharks, to larger species like Frilled, Mackerel and Cow sharks, all the way to the second largest shark in the world, the Basking shark. 

Irish waters provide a refuge for an array of shark species. Tralee Bay, Co. Kerry provides a habitat for several rare and endangered sharks and their relatives, including the migratory tope shark, angel shark and undulate ray. This area is also the last European refuge for the extremely rare white skate. Through a European Maritime and Fisheries Fund (EMFF) project, Marine Institute scientists have been working with fishermen to assess the distribution, diversity, and monthly relative abundance of skates and rays in Tralee, Brandon and Dingle Bays.

“These areas off the southwest coast of Ireland are important internationally as they hold some of the last remaining refuges for angel shark and white skate,” said Dr Maurice Clarke of the Marine Institute. “This EMFF project has provided data confirming the critically endangered status of some species and provides up-to-date information for the development of fishery measures to eliminate by-catch.” 

Irish waters are also home to the Black Mouthed Catshark, Galeus melastomus, one of Ireland’s smallest shark species which can be found in the deep sea along the continental shelf. In 2018, Irish scientists discovered a very rare shark-nursery 200 nautical miles off the west coast by the Marine Institute’s ROV Holland 1 on a shelf sloping to 750 metres deep. 

There are two ways that sharks are born, either as live young or from egg casings. In the ‘case’ of Black Mouthed Catsharks, the nursery discovered in 2018, was notable by the abundance of egg casings or ‘mermaid’s purses’. Many sharks, rays and skate lay eggs, the cases of which often wash ashore. If you find an egg casing along the seashore, take a photo for Purse Search Ireland, a citizen science project focusing on monitoring the shark, ray and skate species around Ireland.

Another species also found by Irish scientists using the ROV Holland 1 in 2018 was a very rare type of dogfish, the Sail Fin Rough Shark, Oxynotus paradoxus. These sharks are named after their long fins which resemble the trailing sails of a boat, and live in the deep sea in waters up to 750m deep. Like all sharks, skates and rays, they have no bones. Their skeleton is composed of cartilage, much like what our noses and ears are made from! This material is much more flexible and lighter than bone which is perfect for these animals living without the weight of gravity.

Throughout history sharks have been portrayed as the monsters of the sea, a concept that science is continuously debunking. Basking sharks were named in 1765 as Cetorhinus maximus, roughly translated to the ‘big-nosed sea monster’. Basking sharks are filter feeders, often swimming with their mouths agape, they filter plankton from the water.

They are very slow moving and like to bask in the sun in shallow water and are often seen in Irish waters around Spring and early Summer. To help understand the migration of these animals to be better able to understand and conserve these species, the Irish Basking Shark Group have tagged and mapped their travels.

Remarkably, many sharks like the Angel Shark, Squatina squatina have the ability to sense electricity. They do this via small pores in their skin called the ‘Ampullae of Lorenzini’ which are able to detect the tiny electrical impulses of a fish breathing, moving or even its heartbeat from distances of over a kilometre! Angel sharks, often referred to as Monkfish have a distinctively angelic shape, with flattened, large fins appearing like the wings of an angel. They live on the seafloor in the coastal waters of Ireland and much like a cat are nocturnal, primarily active at night.

The intricate complexity of shark adaptations is particularly noticeable in the texture of their skin. Composed of miniscule, perfectly shaped overlapping scales, the skin of shark provides them with protection. Often shark scales have been compared to teeth due to their hard enamel structure. They are strong, but also due to their intricate shape, these scales reduce drag and allow water to glide past them so that the shark can swim more effortlessly and silently. This natural flawless design has been used as inspiration for new neoprene fabric designs to help swimmers glide through the water. Although all sharks have this feature, the Leafscale Gulper Shark, Centrophorus squamosus, found in Ireland are specifically named due to the ornate leaf-shape of their scales.

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