An Individual-Based Model of Ontogenetic Migration in Reef Fish Using a Biased Random Walk

Migration is an important component of the life history and ontogeny of reef fish. On the west coast of Florida, the interaction between ontogenetically migrating reef fish and fishing effort is an important contributor to the pattern of fishing mortality. A biased random walk model was developed to represent the movement of red grouper Epinephelus morio from the inshore nursery habitat occupied by juveniles to the offshore reef habitat inhabited by adults on the West Florida Shelf. A simulated tagging study was conducted to develop distributions of movement speed. Time at large, release location, and input movement speed from conventional tagging data were used to parameterize the simulation. Maturity at age, determined when fish began moving, and directional movement behavior were modeled as functions of preferential habitat. The results suggest that the general movement of tagged fish can be represented using simple assumptions. Comparison of the tagging study and the tagging simulation showed no statistical differences between these two in terms of movement speed, distance traveled, mean size of fish at release, and mean size of fish at recapture. Furthermore, the age distribution of the fish arriving at the reef in the model matched the observed age distribution in the commercial catch.