Suitability modeling to delineate habitat essential to sustainable fisheries

A need exists to scientifically determine optimal fish habitats to support decision making for management of essential fish habitat. Scientists have b een collaborating to conduct habitat suitability index (HSI) modeling to sp atially delineate fish habitats for estuarine fish and invertebrate species in Tampa Bay and Charlotte Harbor, Florida. Results from HSI modeling of j uvenile spotted seatrout Cynoscion nebulosus in Charlotte Harbor are presen ted. Data obtained from 1989-1997 by fisheries-independent monitoring in th e two estuaries were used along with environmental data from other sources. Standardized catch-per-unit-effort (catch rates) were calculated across ge ar types using fisheries-monitoring data from Charlotte Harbor and Tampa Ba y. Suitability index functions were determined using three methods: (1) fre quency of occurrence, (2) mean catch rates within ranges, and (3) smooth-me an catch rates determined by polynomial regression. Mean catch rates were e stimated within biologically relevant ranges and, where sufficient data wer e available, for finer intervals across environmental gradients. Suitabilit y index functions across environmental gradients were then derived by scali ng catch rates. Gridded habitat layers for temperature, salinity, depth, an d bottom type in Charlotte Harbor were also created using a geographic info rmation system. Habitat suitability index modeling was conducted using the U.S. Fish and Wildlife Service geometric mean method linked to the ArcView Spatial Analyst module. The model integrated suitability indices associated with the habitat layers for Charlotte Harbor to create a map of the predic ted distribution for juvenile spotted seatrout during the fall season. Suit ability indices developed for Tampa Bay were used with Charlotte Harbor hab itat layers to test transfer of the indices to another estuary. Predicted H SI maps depicted low to optimum habitat suitability zones in Charlotte Harb or. Model performance was evaluated by statistically comparing the relative ranking of mean catch rates with mean suitability indices for correspondin g zones. Suitability indices obtained using polynomial regression methods y ielded more-reliable HSI maps for juvenile spotted seatrout than those deri ved using mean catch rates within biologically relevant ranges. The observe d map, derived using smooth-mean suitability indices transferred from Tampa Bay, was not significantly different (Chi-square goodness-of-fit test) fro m the expected map derived using smooth-mean indices from Charlotte Harbor. Our modeling efforts using transferred indices indicate that it is possibl e to predict the geographic distributions of fish species by life stage in estuaries lacking fisheries monitoring.