Vertical distribution of the planktonic stages of penaeid shrimp.
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In an attempt to describe the vertical diurnal distribution of planktonic stages of penaeid shrimps, Port research cruises into the Gulf of Mexico were made in June, July, September, and November 1963. The plankton was sampled systematically at a station 50 miles south of Galveston, Texas, where water depth approached 36.5 meters. Samples were obtained with a Clarke-Bumpas sampler at 4-hour intervals at each of three depths: 2,18, and 34 meters. Bathythermograph casts were made prior to or at the completion of each collection. During the first three cruises when temperature profiles and visual observations indicated a vertically stable water mass, catch data grouped for all stages indicated that planktonic penaeids were most frequent at and below mid-depth. Data arranged by developmental stage indicated, however, that protozoeal stages were found most frequently near the bottom whereas postlarval stages were at or above mid-depths. Each planktonic stage extended its distribution into the surface layer either just prior to or after darkness. In November, when temperature profiles and visual observations indicated a vertically unstable water mass, planktonic-stage penaieds were more or less homogeneously distributed throughout the water column. There was evidence of movement into surface layer at night by any planktonic stage.