Counterintuitive Responses of Fish Populations to Management Actions

Observed ecosystem responses to fisheries management experiments have often been either much smaller or in the opposite direction of the expected responses based on experience or population models. Examples of these responses can be found even for some very simple experimental management manipulations such as predator and prey manipulations in small lakes and ponds to fish population responses to harvest closures. Such counter‐intuitive prediction failures offer opportunities to identify key processes and variables that are not widely considered in models used to evaluate ecosystem‐based fisheries management policies. A common denominator in the case histories presented are unexpected behavioral responses and strong changes in juvenile survival rates of fish driven by changes in competition, predation, and behavioral responses to predation risk. These factors restructured many of the ecosystems in our simple examples, yet are not widely included in models currently used to evaluate ecosystem‐based fisheries management policies. This represents a critical need in the development of modeling tools to evaluate ecosystem‐based policies based on an iterative process of model building and model testing, using fisheries management actions as probing tools to learn more about the ecosystems being managed.