Methods to Consider Predators in Fishery
May 7, 2013
The Pew Charitable Trusts
Ocean Science Division
Predator-prey relationships can have profound effects on fish populations, but they are generally not considered explicitly in fisheries management. Several methods are available today to incorporate predators, a practical step toward ecosystem-based management.
Managing fisheries is a complex undertaking. This is partly because it is difficult or impossible to directly observe fish populations and the many factors affecting them. So managers and scientists use mathematical models to estimate fish abundance and evaluate possible management actions. At the most basic level, models use estimates of deaths and births, among other things, to calculate how many fish can be caught without reducing the longterm health or productivity of the fishery.
Most of the models in use today focus only on one species. Known as single-species models, they often assume that predators eat a low and constant share of fish. In reality, consumption by predators can vary widely and account for a significant share of the prey population. For example, Overholtz et al. (2008) found that predators take 20 to 40 percent of the Atlantic herring per year in the Gulf of Maine- Georges Bank area. If managers ignore this factor, they risk setting catch limits that are too high.
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