Predators amplify fluctuations in the numbers of small schooling fish

Forage fish are small and densely schooling fish like herring and sardines, that hang out in the open water and become the perfect food for predatory fish, marine mammals, and birds. One key feature of their population numbers is that they have dramatic boom and bust cycles because of ocean conditions, fishing, and highly variable recruitment (numbers of baby fish produced each year). Now, new research shows that increased predation exacerbates the bust part of these cycles, and decreased predation allows for recovery. In addition, variability in predation and ocean conditions has a larger effect than the influence of fishing on forage fish populations, highlighting the key role that natural predators play in regulating the abundance of forage fish. The new paper was written by SAFS postdoc Nis Jacobsen and SAFS professor Tim Essington and appears in the journal Fish and Fisheries.

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