S. F. Treat

Document Type

Statistical Report

Publication Date



We have observed large fluctuations in Tampa Bay fish populations over the last decade, and these changes may be associated with the environment, management practices, or other factors. Staff of the Florida Fish and Wildlife and Conservation Commission’s Fish and Wildlife Research Institute began developing the Fisheries-Independent Monitoring (FIM) program in 1988 and have monitored fish populations in Tampa Bay continuously since 1989. Various types of sampling gear have been utilized during the history of FIM, but 21.3-m bag seines have been used since the beginning of the program. This small seine is effective at capturing juveniles of many economically valuable species (e.g., red drum, Sciaenops ocellatus, and spotted seatrout, Cynoscion nebulosus) and juveniles through adults of many small resident species (e.g., bay anchovy, Anchoa mitchilli, and various species of killifish, Fundulidae and Cyprinodontidae). We present indices of relative abundance for 12 groups of fishes (10 species and two multi-specific categories) in three coarsely delimited habitat types in the Tampa Bay system based on collections made with the 21.3-m seine. We then compare trends within these 36 comparisons to major environmental (i.e., drought) and regulatory (i.e., net ban) events that have occurred during the last decade. Significant differences among years were found in 75% of the comparisons. Comparisons indicating no significant interannual changes in abundance were more than twice as common along bay shorelines as they were in offshore areas of the bay or in the tidal rivers, despite a major change in bay-shore sampling methodology by the FIM program in 1998. One-third of the 36 comparisons indicated significant changes in abundance before and after 1995 (i.e., pre- and post-net ban), and all but one of these trends indicated declines in abundance after 1995. This finding is perhaps not surprising because the fish included in this study were primarily small and would serve as prey for harvestable-sized fishes which may have become more abundant after the net ban. Approximately 47% of our comparisons indicated that changes in relative abundance were related to annual levels of freshwater inflow (scored as either low, moderate, or high), and abundances peaked during years with moderate to high levels of freshwater inflow in more than three-fourths of these comparisons. Among the groups exhibiting maximum abundance during periods of moderate to high inflow were the most abundant species in Tampa Bay, Anchoa mitchilli, and the multi-specific category comprised of all species except A. mitchilli. Although these relationships between abundance and annual inflow must be interpreted with caution, we believe that our results indicate decreased production of small fishes in the Tampa Bay system during periods of drought.


In addition to the input and direction provided by the Steering Committee for BASIS-4, we gratefully acknowledge the wisdom provided by Fred Holland, NOAA Hollings Marine Laboratory for providing his expertise and critique on the status of science and management in Tampa Bay and recommendations for future focus. We also extend our sincere thanks to Ernie Estevez, Mote Marine Laboratory for providing a keynote address which set the tone and historic setting for the symposium.