Developing alternative indices of reproductive potential for use in fisheries management : Case studies for stocks spanning an information gradient

There is accumulating evidence to suggest that spawning stock biomass (SSB) may not bedirectly proportional to reproductive potential. The wide-ranging implications of this conclu-sion necessitate that it be tested for as many stocks as possible. Undertaking such tests iscomplicated by the fact that fish stocks vary in the amount and type of information that isavailable 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 fromexisting data resources. Three stocks had sufficient data to reconstruct a time series of total eggproduction (TEP), whereas, the remaining stocks were limited to estimating proxies for stockreproductive potential.

For some of the case studies the alternative indices explained a higheramount of recruitment variation than did SSB. Other case studies provided evidence that char-acteristics of the spawning stock, e.g. age diversity and female-only SSB, influence recruitmentin ways that are not properly accounted for by using SSB as the sole index of reproductivepotential.

This is further evidence that the assumption of proportionality between SSB andTEP is invalid. The data-rich stocks showed the relationship between SSB and TEP to bevariable and characterized by distinct time trends. This variability will impact the ability ofbiomass-based reference points to conserve reproductive potential.

Consequently, managementprotocols should be adapted to incorporate the detailed information on reproductive potentialthat is increasingly becoming available rather than being restricted to approaches that have beendesigned for data-poor situations.