Assessment of South Florida's Bonefish Stock

of a dissertation at the University of Miami. Dissertation supervised by Professor Jerald S. Ault. No. of pages in text. (194) Florida’s recreational bonefish fishery generates substantial economic benefits to the region; however, the resource has never been adequately assessed to determine standard benchmarks for sustainability. The situation offered a unique opportunity to address unresolved issues in sustainability for a valuable recreational fishery that is almost exclusively catch and release. The goal of this dissertation was three-fold: (1) to develop a comprehensive framework for conducting rigorous stock assessments on recreational catch-and-release fisheries; (2) to apply these methods to the Florida bonefish fishery to compare results against internationally-recognized sustainable fishery benchmarks; and, (3) provide recommendations for longer-term assessment strategies and management efforts. Due to the dearth of available bonefish information, existing literature were synthesized and new quantitative data and models concerning bonefish demographics (i.e. growth, survivorship) and population dynamics were developed. Data for age-and-growth were collected with a focus on both small ( 650 mm FL) bonefish which had been under-sampled in previous research. A twostage growth model was developed that allowed predictions of size-at-age over the complete life history of the species. Evidence from multiple analyses suggested a single species of bonefish in the Florida fishery. A mail survey of bonefish captains (guides) acquired baseline statistics on the south Florida bonefish fishery. Fleet fishing effort is mostly concentrated in the northern Florida Keys (Biscayne Bay to Islamorada) and reflects to some extent bonefish spatial population abundance. The majority of the respondents indicated the stock had declined over the past few decades. A sized-based mortality estimator was used to determine mortality. Changes in current population size from 2003-2010 were determined from a visual survey. Historical stock size was inferred from a relative abundance index from standardized tournament catch rates. Annual trends of the mortality estimates implied a stable population that is not declining which contrasts with the index of abundance and visual survey results. Both the index of abundance and visual survey displayed overall declining trends in recent years. Bonefish movements were determined from anchor tag and acoustic telemetry. Anchor tagging data were analyzed to evaluate movements, stock size structure and mortality. Results revealed no significant relationships between distance moved and days at large or days at large and length at tagging; however, significant individual movements (>100 kilometers) were recorded. Use of acoustic telemetry showed frequent movements around the barrier islands, schooling behavior, and a possible spawning effect with movements to offshore reef habitats. Stock status was addressed with two different classes of assessment models: REEFS, a length-based model which estimated the stock as moderately exploited with the current fishing mortality rate less than the maximum sustainable yield fishing mortality rate; and a “catch-free” age-structured model which indicated a large stock decline over the past 40 years with the stock currently bordering an overfished benchmark. The agestructured model was assumed to be the most robust method because it incorporated the majority of the research data (age and growth, selectivity, mortality, visual survey, CPUE standardization, vessel effort). In conclusion, the stock’s productivity has been significantly reduced over the past 50 years due to fishing, but also degradation of key prey populations, habitats, and water quality, resulting in a current bonefish population that is bordering an overfished state. Recommendations are provided for improving future stock assessments and management approaches. The assessment framework and quantitative methods and models developed here are broadly applicable to bonefish stocks around the world.