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.