Car­ti­lagi­nous fish among our most en­dan­gered


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.

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

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