Estimating habitat related variability in natural mortality of juvenile white shrimp for incorporation into stock assessment models

Comparisons of natural mortality rates can be used to identify essential habitat and nursery areas for fishery species. We estimated and compared natural mortality rates of juvenile white srhimp Litopenaeus setiferus using length-frequency and mark-recapture data and attempted to identify factors that may affect these mortality rates. Daily instantaneous natural mortality rates (95% CI) obtained from the length-frequency data by following individual cohorts over two separate 14-day intervals were 0.043 (0.031 - 0.054) and 0.014 (0.000 - 0.039), while estimates from two catch-curve methods over the combined 14-day intervals were 0.069 (0.042 - 0.095) and 0.060 (0.046 - 0.073). Mark-recapture estimates over 10 days within two separate ponds were 0.129 (0.054 - 0.203) and 0.014 (0.000 - 0.076). These estimates are comparable to previously reported values for this species, but we are the first to report a measure of variability with our estimates. In the mark-recapture experiment, mortality rates appeared to be related to predator abundance in ponds and flooding patterns of the surrounding marsh. The only significant differences occurred between the low length-frequency estimate and three other estimates, but this result should be interpreted with caution because of uncertainty in our estimates, confounding factors between the methods used, and limited data available from other studies. Despite this caveat, the natural mortality estimates and identification of factors affecting variation in mortality of juvenile L. setiferus can be used to improve population models for this species and our understanding of the role of marsh habitats as nursery areas.

The purpose of the Habitat Assessment Improvement Plan (HAIP) is to improve the management of fishery species by promoting an understanding of the link between coastal habitat and fisheries production. This specific project was designed to provide information on mortality rates of juvenile white shrimp during their early-life residence in estuaries. The results will be used to improve stock assessment models for this species.

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data in Microsoft Excel files

Final Report as Microsoft Word file

Mortality estimates from the study were compared with literature values

raw data were proofed for accuracy, and analystical computations were checked for accuracy

A manuscript of this study was reviewed by the SEFSC

A manuscript of this study was approved for publication by the SEFSC.