Stock identity of elasmobranchs in the Northeast Atlantic in relation to assessment and management

Abstract

Fish stock assessment requires that those parts of a species' range can be identified in which the effects of exploitation in particular fisheries are apparent. Thus, fisheries are monitored and regulated in management units largely determined by the distribution of fisheries, areas which may or may not coincide with biological self-perpetuating units. There are several methods of identifying fish stocks, including the interpretation of distribution and relative abundance, tagging studies, genetic analyses and spatial variation in morphometrics, life-history parameters, parasites and contaminants. The natural variability and difficulty in measuring life history and morphological characteristics at the population level suggest that these are not good indicators of stock separation for elasmobranchs. Information on population demography does, however, reveal the relationships between fisheries and resource, and indicates where sampling programmes for the collection of stock assessment data should take place. Tagging studies, in particular, can indicate a stock's main range and migrations, if linked with a good description of the fisheries that are involved with its exploitation. The environmental parameters associated with the distribution of a species are also a useful guide to the likely boundaries of movement. In this paper, we discuss the utility of these approaches to delineate areas to be used for stock assessments of elasmobranchs, and show how biological and fishery information has been used to describe the stock identity for six case study species in the Northeast Atlantic.