Developing Alternative Indices of Reproductive Potential for Use in Fisheries Management: Case Studies for Stocks Spanning an Information Gradient

Abstract

There is accumulating evidence to suggest that spawning stock biomass (SSB) may not be directly proportional to reproductive potential. The wide-ranging implications of this conclusion necessitate that it be tested for as many stocks as possible. Undertaking such tests is complicated by the fact that fish stocks vary in the amount and type of information that is available to estimate reproductive potential. In this review, nine stocks illustrate the range of approaches that are being taken to developing alternative indices of reproductive potential from existing data resources. Three stocks had sufficient data to reconstruct a time series of total egg production (TEP), whereas, the remaining stocks were limited to estimating proxies for stock reproductive potential. For some of the case studies the alternative indices explained a higher amount of recruitment variation than did SSB. Other case studies provided evidence that characteristics of the spawning stock, e.g. age diversity and female-only SSB, influence recruitment in ways that are not properly accounted for by using SSB as the sole index of reproductive potential. This is further evidence that the assumption of proportionality between SSB and TEP is invalid. The data-rich stocks showed the relationship between SSB and TEP to be variable and characterized by distinct time trends. This variability will impact the ability of biomass-based reference points to conserve reproductive potential. Consequently, management protocols should be adapted to incorporate the detailed information on reproductive potential that is increasingly becoming available rather than being restricted to approaches that have been designed for data-poor situations.