Biological correlates of recruitment variability in North Sea fish stocks

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Abstract
There are several hypotheses about the possible significance of different biotic factors on fish recruitment variability. This study presents an exploratory analysis of the possible association of recruitment with the abundance of plankton, which may serveas food for pre-recruits, or the abundance of pelagic and demersal fish, which may prey on pre-recruits. The analysis was undertaken using recruitment data from seven North Sea fish stocks, plankton data from the Continuous Plankton Recorder series, biomass of adult herring, a dominant planktivore, and biomass of adult cod, an important predator of fish. Results indicate that recruitment variabilityin most stocks appears to be independent of the long-term changes in the abundance of plankton, adult herring, or cod. Detrending the time series reveals that short-term variability inrecruitment is associated with changes in the abundance of potential prey and predators of pre-recruits. The dominant association is between fluctuations in recruitment and plankton abundance. The contrasting results, before and after detrending, are due to highly correlated decreases in both plankton (prey) and fish (predator)abundance which may have resulted in simultaneous decreases in both development and mortality rates. This could potentially mask their association with fluctuations in recruitment.

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