The importance of habitat and life-history for extinction risk in sharks, rays and chimaeras

VERÓNICA B. GARCÍA; LUIS O. LUCIFORA; RANSOM A. MYERS

Itajaí

Congreso; V Reunião da Sociedade Brasileira para o Estudo dos Elasmobrânquios; 2006

Spccies with low productivity, i.e. sniall litters, slow growth rates. latc sexual nlaturity and long interbirth interval are less able to coinpensate for ~ncreased mortality and are thereforc inore vulnerable to extinction. Since life histories are largely shaped by tlie environment, we predict that choiidricthyans Goln deep sea environments, the most unproductive marine habitats, will be less productive and more vulnerable to extinction than species lrom continental shelves and tlie open ocean. To test these hypotheses, we first compared age at maturity, growth rate (von Bcrtalanffy's k) and longevity (maximum observed age) of 98 species of sharks, rays and chimaeras, from continental shelves, the iinpor~ance of thc the open ocean and the dcep sca. Second. we co~npared habitat and life history traits (body size, reproductive mode, interbirth interval, litter size) in deterinining thc extinction risk, nieasured as thc fishing mortality needed to drive a species to extinction. Controlling for phylogenetic correlatio~i, generalized linear mixed ~nodelsand generalized estimating equations show that deep-sea choildrichthyans have a higher age at inaturity and longevity, and a lower growth rate than shallow-water species. llalf the fishing mol-tal~ty needed to drive shclf and oceai~ic chondrichthyans to extinction is sufficient to eradicate deep-sea chondrichthyans. Reproductive mode, interbirth intei-val arid body size are significantly associated to extinction risk, whcrcas litter sizc has a non-significant effect. Extinction risk varied taxononiically with sharks of tlie order Squaliforines being the most vulncrable to extinction aiid skatcs (order Rajifonnes), the least vulnerable. Age at maturity, growth rate and extinction risk were highly correlated with phylogeny. As a consequence, the loss of species will be accompanied by a loss of pliylogenetic diversity. Conservation priority should not be restricted only to large species since Illany small species, like those inhabiting the dccp ocean, are also highly vulnerable to cxlinclion. Fishing ~liortality of deep-water chondrichthyans already exploited should be mini~nized, and new dcep-watcr fisherics for sharks should be prevented.