Assessing Variability in Juvenile Brown Shrimp Growth Rates in Small Marsh Ponds: An Exercise in Model Evaluation and Improvement

Brown shrimp Farfantepenaeus aztecus support a commercially important fishery in the northern Gulf of Mexico, and the juvenile shrimp use coastal estuaries as nurseries. Production of young shrimp from these nurseries, and hence commercial harvest of adults from the Gulf, is highly variable from year to year. Our recently published, individual-based model attempted to explain this variability as a function of habitat and the environmental factors such as temperature, salinity, and access to intertidal marsh habitat. We conducted a mark-recapture field study between April 12 and June 9, 2011, to provide growth rate data for model testing, as well as to further examine factors that affect growth, including available food biomass. Brown shrimp growth rates were measured in three polyhaline marsh ponds over periods of 2 to 4weeks. We recorded hourly temperature and flooding data and measured biomass of infaunal food organisms. We parameterized our production model with input from 2011 to compare modeled output with observed data. Mean growth rate estimates from the model were similar to the estimated mean growth rate observed in the field (1.13mm/d and 1.06mm/d, respectively); however, field growth rates differed significantly among three marsh ponds (1.02, 1.03, and 1.26mm/d). Data on infaunal biomass suggest that spatial and temporal variability in available food organisms is related to differences in shrimp growth, and the inclusion of such information may enhance the model.