Temporal effects of dredging and dredged material disposal on nekton in the offshore waters of Galveston, Tex., with notes on the natural histories of the most abundant taxa.

The temporal effects of dredging and dredged material disposal on nearshore nekton off Galveston, Texas, were studied from May 1975 through May 1976. Statistical and computerized comparisons of trawl samples between dredged material disposal areas and areas not affected by dredging or disposal indicated few differences between the sites. Few differences existed between stations regarding numbers of individuals, species, or biomasses, as well as the length-weight relationships and feeding habits of the dominant fishes. Differences between sampling areas were attributed to natural nekton distributions. Dredging and dredged material disposal did not appear deterimental to nekton; some nekton may have been attracted to the turbid waters of the dredged and disposal sites during dredging activities. The turbid water may have been attractive by offering food as well as protection from larger sight-feeding predators. Conversely, other data indicated reduced numbers of nekton in the disposal area soon after disposal activities; nekton appeared to return to the area within one month following cessation of dredged material disposal, perhaps in correlation to recolonization of the area by benthic food species. A total of 49 vertebrate species representing 31 families and 54 invertebrate species representing 28 families were collected during the study. Seven families constututed 97% of the catch by numbers. The included Sciaenidae, Penaeidae, Portunidae, Carangdae, Polynemidae, Cynoglossidae, and Squillidae. Ten fish species and 10 invertebrate species comprised 96% of the total catch. The area was characterized by a sciaenid-penaeid community, wiht the most dominnant species being Micropogon undulatus and Trachupeneus similis. Most species were estuarine dependent. Stomach analyses of 22 fish species indicated the dominant fishes to be demersal feeders. A minimum of 74 prey genera/species were identified, with polychaetes and small crustaceans being the most abundant prey. The largest sample by numbers was collected in February. i.e. predominantly juvenile M. undulatus and T. similis. The largest biomass was collected in August due to schooling Chlorosconbrus chrysurus in the disposal area. The highest and lowest species diversities occurred during the summer-fall and winter-spring, respectively. Multidimensional cluster analysis delineated nekton seasonality. Immigration of adults from Galveston Bay occurred in the Fall, with subsequent immigration of juveniles the following spring. The Galveston Ship Channel appeared to be used as a pathway for these migration. Individuals collected were generally less than 200 mm in total length, and annual mortality rates appeared to be over 90%.