Environmental factors affecting burrowing by brown shrimp Farfantepenaeus aztecus and white shrimp Litopenaeus setiferus and their susceptibility to capture in towed nets

Laboratory experiments were conducted under simulated daytime conditions to examine the effects of salinity, sediment texture, size, density, and hunger on burrowing behavior of juvenile brown shrimp Farfantepenaeus aztecus and white shrimp Litopenaeus setiferus. Over all experimental conditions (20,929 observations of 2411 individual shrimp), 77.5% of brown shrimp and 21.4% of white shrimp were observed burrowed with more than half of their body beneath the substrate. The tendency of burrowed shrimp to emerge from burrows when disturbed also was tested. When burrowing rates were examined in combination with this tendency to emerge upon disturbance, only 46.7% of brown shrimp would be susceptible to capture in towed nets, while almost all (97%) white shrimp would be susceptible. All environmental factors examined in this study, except salinity for white shrimp, significantly affected burrowing of these species. When these environmental effects on burrowing were combined with the likelihood of emergence, however, the effects of salinity and substrate type on brown shrimp behavior appeared most likely to affect capture by towed nets. Estuarine abundance indices from resource surveys using towed nets could be adjusted using such vulnerability estimates.