Demographic analysis as an aid in shark stock assessment and management

The use of demographic analyses incorporating life history information on v alidated age and growth, reproduction, and natural mortality is proposed to gain insight into the population dynamics of sharks under a variety of sce narios and to assess their vulnerability to varying exploitation rates. Thi s approach provides a useful framework for comparison with other currently used methods of assessment, especially those that rely only on fishery-depe ndent data, and thus can be helpful to stock assessments and to the rationa l exploitation and management of shark stocks. A review of demographic anal yses of large coastal shacks on the east coast of the US indicates that the lemon and sandbar sharks have very low rates of population increase (r<1.2 % year(-1)) and are thus extremely vulnerable to exploitation. In contrast, one of the small coastal group species of lesser importance to the fisheri es, the bonnethead shark, has some of the highest r values yet calculated f or any shark. Preliminary demographic analyses using nonvalidated age estim ates indicate that two other common and economically valuable large coastal species, the blacktip and dusky sharks, may also exhibit relatively slow r ates of population change and be very vulnerable to overexploitation, Impro ved assessment of shark stocks requires increased collection of biological and fishery data and a much- better understanding of their population dynam ics, especially stock-recruitment relationships. (C) 1998 Elsevier Science B.V. All rights reserved.