Abstract
To improve fishery management, there is an increasing need to understand the long-term consequences of natural and anthropogenic climate variability for ecological systems. New England’s iconic cod populations have been in decline for several decades and have recently reached unprecedented lows. We find that 17% of the overall decline in Gulf of Maine cod biomass since 1980 can be attributed to positive phases of the North Atlantic Oscillation (NAO). This is a consequence of three results: i) a 1-unit increase in the NAO winter index is associated with a 17% decrease in the spring biomass of age-1 cod the following year; ii) this NAO-driven decrease persists as the affected cohort matures; iii) fishing practices appear to exacerbate NAO’s direct biological effect such that, since 1913, a 1-unit increase in the NAO index lowers subsequent cod catch for up to 19 years. The Georges Bank cod stock displays similar patterns. Because we statistically detect a delay between the NAO and subsequent declines in adult biomass, our findings imply that observed current NAO conditions can be used in stock forecasts, providing lead time for adaptive policy. More broadly, our approach can inform forecasting efforts for other fish populations strongly affected by natural and anthropogenic climatic variation.
Highlights
Many of the world’s commercial fisheries are in decline, raising concerns about both food security [1,2,3] and ecosystem functioning [2, 4]
There is a negative relationship between the North Atlantic Oscillation (NAO) index and cod biomass
For the Gulf of Maine stock from 1971–2013, a 1-unit increase in the NAO index, which increases winter sea surface temperatures (SST) by .045°C (Table A in S1 File), during a cohort’s birth year is associated with a 17% drop in surveyed biomass for that cohort at age 1
Summary
Many of the world’s commercial fisheries are in decline, raising concerns about both food security [1,2,3] and ecosystem functioning [2, 4]. Recent literature has highlighted the need to uncover the role of environmental conditions, climate variability, in driving fish populations [5,6,7,8,9]. It remains to be determined, whether such relationships can help improve stock management. In 2014, the National Oceanic and Atmospheric Administration (NOAA) instituted an unprecedented six-month ban on all Gulf of Maine stocks after the 2014 stock assessment detected historically low biomass levels [14]. To PLOS ONE | DOI:10.1371/journal.pone.0158487 July 27, 2016
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