Fisheries population models often treat demographic parameters as constant across large spatial scales. But spatial variation in habitat-dependent processes may be important to population dynamics, especially for species with spatially structured life histories, like gag (Mycteroperca microlepis). With the development of new acoustic telemetry technology we are now able to relate gag space-use to landscape structure at appropriate scales. Juvenile gag in the Gulf of Mexico spend 2-6 years moving across the continental shelf before spawning in deeper waters. Gag establish residency on infrequent reefs and forage across the landscape of low-relief, sand-bottom and live-bottom habitats. A trade-off between foraging success and predation risk is predicted to influence space-use patterns (i.e. kernel density estimates of home range) differently in the two habitats.
We ask how space-use differs between gag living in sand-bottom and live-bottom landscapes? With side-scan sonar imagery we create categorical habitat maps of the seafloor surrounding 3 experimental reefs in sand-bottom landscapes and 3 reefs in live-bottom landscapes. Using new telemetry technology, we tag 8 individuals per reef recording positions as often as every 2s for 14d with sub-meter performance over 250m. We relate space-use patterns to landscape composition and environmental conditions (e.g. water velocity, temperature).
Results/Conclusions
Comparing 90% kernel density estimates, we find that gag on sand-bottom reefs use, on average 361m2 while those on live-bottom reefs use, on average 1341m2 (t(4.90), df=4, p=0.004). These preliminary results suggests that gag are making space-use decisions in a way that balances foraging success and predation risk in response to landscape structure. Our continuing work will extend this habitat/space-use interaction to impacts on recent growth and future fecundity. Understanding this linkage is the first step towards incorporating habitat variation across the continental shelf into fisheries population models. As fisheries management tools become increasingly spatial (e.g. marine protected areas, artificial habitat enhancements) a better understanding of the relationship between landscape structure and space-use will increase management effectiveness and foster conservation. For the first time, new telemetry technology allows us to address space-use questions for gag and other fisheries species in their natural environment and at appropriate scales.
