Re-evaluation of the environmental dependence of Pacific sardine recruitment

• Published in: Fisheries research 2019-08, Vol.216, p.120-125
• Main Authors: Zwolinski, Juan P., Demer, David A.
• Format: Article
• Language: English
• Subjects: Environment; Management; Prediction; Recruitment
• ISSN: 0165-7836; 1872-6763
• DOI: 10.1016/j.fishres.2019.03.022

•Environmentally informed stock-recruitment relationships are volatile and require frequent verification.•The SST index used to calculate the harvest guideline for Pacific sardine does no longer explain the stock’s productivity.•Proxies for fish stocks productivity are fallible and should be avoided in management rules. The environment influences the recruitment of small pelagic fishes, so environmental indices are used to match fishing mortalities to the stocks’ productivities. For example, the exploitation fraction for the northern stock of Pacific sardine in the Northeastern Pacific is a function of sea-surface temperature (SST). The functional relationship changes, however, because our perception of the environmental effects on sardine recruitment is based on assessment models that are periodically updated with new input data and assumptions. In this paper, we use data from recent stock assessments to re-examine previously identified correlations of sardine recruitment success (the logarithmic ratio of recruitment and spawning stock biomass) with indices of SST off Southern California and the Pacific Decadal Oscillation (PDO). We show that the earlier correlation with SST is likely invalid, and the persistent correlation with the PDO is weaker. Because many environmental stock-recruitment relationships fail upon re-examination, environmental proxies for fish productivity might not always prescribe the correct amount of fishing mortality and should be avoided. Alternatively, for species assessed periodically, dynamic fishing mortalities could be based on measurements of recent stock productivity inferred directly from surveys, or from the results of analytical assessments based on those observations.