Data from: New England cod collapse and the climate

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.