From August 30 through September 3, 1964, duplicate (clockwise and counterclockwise) semicircular tows of 100-ft radius were made with the Renfro beam trawl every 2 hours over a 98-hour period. The sampling site was a tidal flat adjacent to the shoreline at Cheniere la Croix, Louisiana,
bordering the Gulf of Mexico. A total of 9,462 postlarval white shrimp, Penaeus setiferus (Linnaeus), were captured. Because the standard deviation of catches (numbers of postlarvae) taken in duplicate tows was proportional to the arithmetic mean of duplicate catches, the geometric
mean catch per tow was used as a measure of relative abundance of postlarvae. Peak catches of postlarvae per tow occurred at night, 2-4 hours after high water and at the lowest water temperature, during each of the four 24-hour periods. Minor peak catches occurred each afternoon near the low-water
stage and at the highest water temperature during each 24-hour period.
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