White shrimp emigration in relation to size, sex, temperature and salinity.
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This study was conducted on juvenile and subadult white shrimp, Penaeus setiferus (Linnaeus), emigrating from Galveston Bay, Texas, to the Gulf of Mexico. Surface, midwater, and bottom tows were made with a 3-m otter trawl on ebbing tides from 1 August 1966 to 27 January 1967. Sampling was usually conducted during the day. Five peaks of emigration occurred from 19 October through 25 December, coinciding with water temperatures between 19 degrees and 8 degrees C in the tidal pass. The catch per unit of effort increased significantly from the surface to the bottom of the water column. Sharp drops in water temperature appeared to stimulate shrimp emigration. The mean lengths of shrimp caught were similar between water depths and sexes on a given sampling date, but decreased with progress of the season and decreasing temperature; there was no obvious relation between length and salinity. Of 2,964 white shrimp caught in the tidal pass, 55.1 percent were females, but the sex ratio was not significantly different from 1:1.