Abstract
In order to provide better fisheries management and conservation decisions, there is a need to discern the underlying relationship between the spawning stock and recruitment of marine fishes, a relationship which is influenced by the environmental conditions. Here, we demonstrate how the environmental conditions (temperature and the food availability for fish larvae) influence the stock–recruitment relationship and indeed what kind of stock–recruitment relationship we might see under different environmental conditions. Using unique zooplankton data from the Continuous Plankton Recorder, we find that food availability (i.e. zooplankton) in essence determines which model applies for the once large North Sea cod (Gadus morhua) stock. Further, we show that recruitment is strengthened during cold years and weakened during warm years. Our combined model explained 45 per cent of the total variance in cod recruitment, while the traditional Ricker and Beverton–Holt models only explained about 10 per cent. Specifically, our approach predicts that a full recovery of the North Sea cod stock might not be expected until the environment becomes more favourable.
Highlights
For both fisheries and conservation purposes, a major challenge is to understand how environmental change influences marine ecosystems [1,2]
The combined Ricker– Beverton – Holt model, where the North Sea cod stock – recruitment relationship is influenced by both zooplankton abundance and sea temperature, had the lowest Akaike Information Criterion (AIC) value and the most support from the available data series
When the zooplankton index was low, the model indicated a positive relationship between spawning stock biomass and recruitment until the stock reached about 50 000 tonnes; above this level, the model predicted a negative relationship between spawning stock and recruitment
Summary
For both fisheries and conservation purposes, a major challenge is to understand how environmental change influences marine ecosystems [1,2]. We apply this model to long-term data on cod (Gadus morhua L.) in the North Sea, where excellent long-term data on zooplankton (i.e. food for fish larvae) are available [18].
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