Demographic analysis as an aid in shark stock assessment and management

Abstract

The use of demographic analyses incorporating life history information on validated age and growth, reproduction, and natural mortality is proposed to gain insight into the population dynamics of sharks under a variety of scenarios and to assess their vulnerability to varying exploitation rates. This approach provides a useful framework for comparison with other currently used methods of assessment, especially those that rely only on fishery-dependent data, and thus can be helpful to stock assessments and to the rational exploitation and management of shark stocks. A review of demographic analyses of large coastal sharks 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 fisheries, the bonnethead shark, has some of the highest r values yet calculated for any shark. Preliminary demographic analyses using nonvalidated age estimates indicate that two other common and economically valuable large coastal species, the blacktip and dusky sharks, may also exhibit relatively slow rates of population change and be very vulnerable to overexploitation. Improved assessment of shark stocks requires increased collection of biological and fishery data, and a much better understanding of their population dynamics, especially stock–recruitment relationships.