Monday 23 October 2017

Cartilaginous fish among our most endangered

By Jim Hurley - Nature Trail

The Porbeagle is a shark on the verge of extinction in Irish waters.
The Porbeagle is a shark on the verge of extinction in Irish waters.

If you pinch the base of your nose between finger and thumb you feel that it is made of hard bone. Do the same to the tip of your nose you note that it is soft, flexible and rubbery because it is made of cartilage. Our ears are also made of cartilage.

Fish are divided into two great groups: bony fish and cartilaginous fish. The bony ones like Cod and Salmon have hard bones. All the others have skeletons made of cartilage. Even their teeth are hard cartilage. Common examples of cartilaginous fish are sharks, dogfish, rays and skates.

The recently published Red List for cartilaginous fish reveals that we have 71 species of them in Irish territorial waters, over half the total number recorded in Europe.

The fossil record shows that cartilaginous fish evolved at least 420 million years ago, and rapidly diversified to become one of the most species-rich groups of predators on Earth. While they have been around for far longer than humans have been, some of them are facing extinction due to our activities.

The main human impacts on threatened species are over-exploitation via by-catch by commercial fisheries, habitat destruction and disturbance.

Natural factors operating against them are that they include some of the latest maturing and slowest reproducing of all vertebrates, resulting in very low population growth rates with little capacity to recover from overfishing and other threats such as pollution or habitat destruction.

The team that drew up the recent Red List involved experts from the Marine Institute, Inland Fisheries Ireland, the Irish Elasmobranch Group, the Department of Agriculture, Environment and Rural Affairs in Northern Ireland, the National Biodiversity Data Centre and the National Parks and Wildlife Service.

Of the 71 species occurring in Irish waters, there was sufficient data to assess 58. The five Red List categories in order of severity are: 'Critically Endangered' (facing extinction), 'Endangered', 'Vulnerable', 'Near Threatened' and 'Least Concern' (common and widespread).

Six species were assessed as 'Critically Endangered': Portuguese Dogfish, Common or Blue Skate, Flapper Skate, Porbeagle shark, White Skate and Angel Shark.

A further five species were assessed as 'Endangered': Leafscale Gulper Shark, Basking Shark, Common Stingray, Undulate Skate and Spurdog.

Six species were assessed to be 'Vulnerable': Longnose Velvet Dogfish, Kitefin Shark, Tope, Shagreen Ray, Longnose Skate and Cuckoo Ray.

Of the remaining species, nineteen were assessed as 'Near Threatened' and twenty-two as 'Least Concern'.

The full Red List of cartilaginous fish can be accessed at

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