Variation in whole-, landed- and trimmed-carcass and fin-weight ratios for various sharks captured on demersal set-lines off eastern Australia

Abstract

Sharks are important apex predators in marine systems but many populations have experienced large declines, which has resulted in adverse effects on marine food webs. Sharks are also economically important, as their fins are valued in Asian markets. In response to concerns about declining shark populations, a number of nations, including Australia, have developed national plans of action for their conservation and management. As part of New South Wales' (NSW) efforts to understand the characteristics of their shark fishery, data were collected on the depth of capture, species, sex, body length and weight, fin weight, and reproductive status of individuals caught in the NSW commercial 'large shark' demersal set-line fishery. We created models of the relationship between fin to body weight and wastage (discarded or low value portions of the carcass) and compared the ratios of whole, landed, trimmed, and fin weight to determine the relationship between fin weight and wastage to length by species. Our results indicate that length, sex, and the interactions between length with species and sex account for differences in the relative fin weight of sharks; whereas species, length, and their interaction account for differences in the proportion of a shark carcass that is wasted. The data reveal that catching smaller sharks will increase relative fin weight and decrease wastage. Given these results, we recommend that managers consider weight ratio data information in their decision making to promote a sustainable and profitable shark fishery.