Ecological observations on penaeid shrimp in Mobile Bay, Alabama

Twelve stations in Mobile Bay were sampled monthly with an otter trawl for 27 consecutive months. Twelve shore and ten nearshore stations were sampled concurrently. All shrimp taken were measured. Water salinities and temperatures were recorded* Primary recruitment of brown shrimp extended from April to November. During that time they concentrated in water 2 to 3 feet deep with attached vegetation. In winter they grew about 12 to 18 mm per month; in spring and summer about 35 mm per month, with growth as much as 50 mm per month in the very young. Primary recruitment of white shrimp extended from June to September. They concentrated in water less than 2 feet deep in areas with large amounts of organic detritus. In winter they grew 13 to 27 mm per month; in summer 18 to 31 mm per month, with growth as high as 65 mm per month in the very young. In general, post-juvenile shrimp of both species (75-80 mm) move from the shallower to the deeper parts of upper Mobile Bay, then to the lower bay and finally to the Gulf of Mexico. Larger shrimp are always found in the lower bay area. The movement pattern of brown shrimp precedes that of white shrimp by about three months. Fishing pressure is intense. During June, July, August, and September the monthly catch of brown shrimp may exceed the amount available at any given time in that month. About half the available white shrimp are taken each month from August to December