Composition, ecology, and dynamics of demersal fish communities on the northwestern Gulf of Mexico continental shelf, with a similar synopsis for the entire Gulf.
Two major communities of demersal fishes are found over soft bottom on the continental shelf in the northwestern Gulf of Mexico inshore of the 91 m (50 fm) contour: 1) a white shrimp grounds community located at about 3.5-22m (2-12 fm) and 2) a brown shrimp grounds community located at about 22-91 m (12-50 fm). The overall and seasonal composition of these ichtyofaunas are described and their community ecology is discussed. The faunas of the two shrimp grounds were distinct at the family level except that a zone of faunal overlap occurred at 18-36m (10-20 fm). Most species that were abundant on one shrimp grounds were absent or virtually absent on the other. The fish communities were structurally similar on the two shrimp grounds in that a single species and family dominated each community. These taxa were Micropogon undulatus and the family Sciaenidae on the white shrimp grounds, and Stenotomus caprinus and the family Sparidae on the brown shrimp grounds. Most species were not abundant. The ichthyofauna was richer on the brown shrimp grounds than on the white shrimp grounds. The demersal ichtyofauna was richest in the cold months, especially on the brown shrimp grounds. The fishes of the white shrimp grounds have a strong affinity for estuaries whereas the fishes of the brown shrimp grounds are independent of estuaries. Relative biomass was much higher on the brown shrimp grounds than on the white shrimp grounds. Relative biomass was much higher in summer than during winter, especially on the white shrimp grounds. Overall,11.35 volumes of discard were landed to one volume of headed shrimp. We estimate that about 219,040 metric tons (483 million lb) of fish were discarded annually in the Gulf by Texas.