Alternate Title

Variability in Estimating Abundance of Postlarval Brown Shrimp, Farfantepenaeus aztecus (Ives), Migrating into Galveston Bay, Texas

Document Type



Three sets of monitoring data were used to examine the variability associated with abundance estimation of postlarval brown shrimp, Farfantepenaeus aztecus (Ives) in Bolivar Roads, Texas—the main connection between the Gulf of Mexico and Galveston Bay. Abundance of postlarvae (PL) caught with Renfro beam trawl varied greatly in different years on the same dates. A “spring peak” of brown shrimp PL migrating into Galveston Bay was found for 2 April with a quadratic regression fit to 6-day moving averages of daily mean abundance from 22 yrs of monitoring data: Ln(PL+1) = 0.8736 + 0.09037Day - 0.0004934Day2 (adj-R2 = 0.83, n = 159), where Day is Julian day. Abundance varied by four orders of magnitude (0 to 24,616 PL/tow) in just 4 d during a four-week intensive monitoring of PL during the 1987 spring peak. Abundance also varied by three orders of magnitude between the North and South Jetty sites during the same collection time. During a third study, PL abundance varied by two orders of magnitude along 360 m of the beach in < 4 hr. These investigations demonstrate that detecting significant differences in PL shrimp abundance in a pass requires substantial sampling that may not be logistically possible. However, best estimates could be obtained by including as many dates as possible, followed by including more sites, and finally by collecting during both day and night. Conclusions drawn from abundance studies of PL shrimp, fish, and crab immigrants through estuarine passes that are based on only a few samples should be reviewed.

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