Mapping of the Biological Resources of the Continental Shelf

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Abstract
Distribution patterns of the penaeid shrimp and demersal fish species are discussed based upon collections totaling in excess of 330,000 shrimp and 2,245,000 fishes. Depth related zonation reveals nearshore, mid-shelf, outer shelf, and trans-shelf assemblages. Estuary related species are particularly prominent on the northwestern Gulf shelf, while rock and reef related species are most important in the fauna of the eastern Gulf shelf. Recognizable elements in the shelf fauna also include species of tropical affinity; open ocean and upper slope species; inhabitants of seagrass beds, mangrove swamps, and carbonate rubble and shell hash; burrowers in soft bottoms; and inhabitants of the upper water column. The eastern Gulf shelf is inhabited by twice as many fish species and eight times as many unique species as the northwestern shelf, reflecting the great diversity of habitat types in the eastern Gulf. A few key species numerically dominate the ichthyofauna of the northwestern shelf, but dominance is spread through many species in the east. Seasonal shifts in species density primarily reflect inshore/offshore seasonal migrations of estuary related species, but seasonal inshore/offshore density shifts are also observed among the true shelf residents. Trophically the shelf systems are supported by precipitated plankton and organic detritus derived from rivers, bays and estuaries, seagrass beds, and mangrove swamps, although attached algae are also important producers in the east. Mollusks, polychaetes, and small crustaceans which feed upon this material, in turn, support the demersal fish communities whose species are generally short-lived. Larger longlived predators are mostly seasonal migrants which appear in the northern Gulf during the warmer months. Bottom-feeding generalists are prominent in the northwest, while specialists are in great evidence in the east. These distributional studies lay the foundation for understanding the shelf ecological systems, and they also provide a basis for informed management decisions.

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