Growth and mortality of juvenile white shrimp Litopenaeus setiferus in a marsh pond

Despite the widely held view that certain estuarine habitats are more valuable as nurseries because they provide enhanced growth and reduced mortality, there remain few estimates of growth and mortality rates in support of this paradigm. We conducted field caging experiments and collected weekly nekton samples in shallow open-water habitat in a marsh pond during summer and fall 2007 in Galveston Bay, Texas, USA, to estimate growth and morality rates of juvenile white shrimp Litopenaeus setiferus. Growth rates (mean +/- 1 SE) were lower during the summer experiment (0.77 +/- 0.05 mm d(-1)) than the fall (0.91 +/- 0.04 mm d(-1)), and high summer water temperatures may have inhibited shrimp growth. Cohort analysis to derive mortality estimates from 15 weekly sampling trips failed due to extended periods of continuous recruitment, the lack of clearly identifiable cohorts, and high temporal variability in abundance estimates. Catch-curve analysis provided estimates of mean daily instantaneous mortality (Z) during the sampling period of 0.181 for post-larvae and early juveniles <28 mm TL and 0.083 for larger juveniles >28 mm. The mortality estimates must be interpreted with caution due to potential problems meeting the assumptions of catch-curve analysis. Despite the challenges, comparisons of vital rates among habitats are required to validate long-held paradigms on the functioning of estuarine nurseries and the importance of various coastal habitats in the support of fishery species.