Ideal free distributions in fleet dynamics: a behavioral perspective on vessel movement in fisheries analysis

Since fleet dynamics was defined in the 1980s there has been increasing interest in the role played by vessel behavior in the exploitation of aquatic resources. The ideal free distribution (IFD), from behavioral ecology, has proved useful for examining the relationship between vessel and resource distributions in commercial fisheries. When making inferences based upon the IFD it is critical to examine its underlying assumptions, particularly the form of competition between fishing vessels. When present, an IFD can decouple the relationship between local catch rates and abundance, obscuring declines in smaller or weaker fish stocks. As an alternative, probabilistic methods have also been successfully applied to the study of vessel behavior. However, parsimonious behavioral models like the IFD will often be preferable because (i) they can be examined using the data typically available from commercial fisheries, (ii) they require fewer data than probabilistic models, and (iii) they are easily incorporated into more complex management models as the fishing component. Where deviations from the IFD occur they can provide insights into the relationship between regulations, environment, and vessel activities that will improve our interpretation of the data generated by commercial fisheries.