Is spawning stock biomass a robust proxy for reproductive potential?

• Published in: Fish and fisheries (Oxford, England) England), 2016-09, Vol.17 (3), p.596-616
• Main Authors: Kell, Laurence T, Nash, Richard D M, Dickey-Collas, Mark, Mosqueira, Iago, Szuwalski, Cody
• Format: Article
• Language: English
• Subjects: Animal reproduction; Biomass; Brackish; Clupea harengus; Egg production; Fisheries management; Gadus morhua; Marine; Pleuronectes platessa; reference points; regime shifts; reproductive potential; spawning stock biomass; stock recruitment; Time series
• ISSN: 1467-2960; 1467-2979
• DOI: 10.1111/faf.12131

Reference points based on fishing mortality (F) and spawning stock biomass (SSB) are a requirement of many fisheries management frameworks. SSB is assumed to be a proxy for stock reproductive potential (SRP). Limit reference points based on SSB are used to indicate the level of biomass below which productivity is affected. SSB fails to account for changes in fecundity, egg viability and sex ratio, and it has been argued that total egg production (TEP) provides a better reflection of SRP. We explore how accounting for TEP impacts limit reference points and evidence for a relationship between stock and recruit. Time series of SSB and TEP are compared for three North Sea stocks: cod (Gadus morhua), herring (Clupea harengus) and plaice (Pleuronectes platessa). Dynamics based on TEP are different from those based on SSB for cod and plaice, but the stock–recruit relationships were not ‘improved’ using TEP. Shifts in productivity (spawner per recruit) occur in all three time series and SSB underestimated uncertainty. Yet again, it was shown that assumptions of stationarity about fish population productivity are incorrect. We argue that the use of TEP does improve the realism in our understanding of stock dynamics, and demographically, more complex management strategy evaluation is required to develop management procedures that are robust to uncertainty and integrate F and the demographic health of a stock. Empirical feedback control systems based on fisheries independent indices including surveys of eggs, larvae, recruits, juveniles or spawning adults should be evaluated and compared to traditional approaches.