Effects of gas and oil field structures and effluents on pelagic and reef fishes and macrocrustaceans
Abstract
From the Abstract: “Demersal nekton communities in the Buccaneer Oil Field during research year 1978–1979 were dominated by macrocrustaceans, particularly sugar shrimp, Trachypenaeus similis. The most abundant fish was the shoal flounder, Syacium gunteri. Results of cluster analysis performed on the trawl data indicated three distinct faunal assemblages. Of these, the assemblage grouping all the surmer collections was the most dissimilar. The winter collections and the fall collections taken at Production Platform 296 comprised a second distinct cluster whereas the remaining fall collections and all spring collections represented the third major grouping. We interpreted the results to indicate that there were two distinct biological seasons (summer and winter) separated by spring and fall periods of transition.
Based upon analysis of variance performed on the Shannon-Weaver index (H"), species diversity of the demersal nekton community at control sites was significantly lower than diversity at structures with discharges. Richness of species was generally similar between the two types of structures, but collections taken at control sites were usually strongly dominated by a seasonally abundant form. The resulting lack of evenness of species in collections taken at the control sites'contributed towards the significantly lower diversity indices observed there as opposed to that at structures with discharges.
The effects of substrate and platform type on seasonal and areal distributional patterns are provided for dominant, demersal species. Several important species, including sugar shrimp, were indicated more abundant at production platforms than at control structures having the same bottom type. However, within the production platform group, most of the species examined were usually significantly more abundant at P288A (intermittent discharge) than at P296B (continuous discharge).
Atlantic spadefish, Chaetodipterus faber, populations were atypically low at Production Platform 296B in summer 1978, and populations at all structures in the Buccaneer Oil Field suffered a disease epidemic during winter. The disease epidemic was believed to have been related to contaminant discharge. This was the second consecutive winter that spadefish disease epidemics have been observed in the field. Bluefish, Pomatomus saltatrix, in contrast to the previous year, were scarce or absent in summer 1978. However, as has been observed previously, they were abundant in the study area during other seasons.
Red snapper, Lutjanus campechanus, were most abundant during the fall and spring seasons; their low abundance during summer and winter coupled with their non-migratory habitats and the observed heavy fishing pressure in the field, indicate that most of the red snapper recruited to the field were harvested by sportfishermen. we found no evidence of detrimental effects of the discharge on red snapper populations. Base upon the size or age distribution, the oil field population appears overfished, and, we suspect that on a gulf-wide basis, the entire fishery is probably badly in need of regulation or other management.
Sheepshead, Archosargas probatocephalus, were found to be a "structure-faithful" species and evidence that resident oil field populations were subject to a higher level of parasitism than were nonresident populations was obtained. The results of this year's program has provided the first indication that sheepshead undergo spawning migrations and/or aggregate at offshore structures for spawning. The Buccaneer Oil Field is a spawning site for this species.
The crested blenny, Hypleurochelus geminatus, was more abundant at sites near the discharges on production platforms than at any other location in the field. Such sites offer proportionately more habitat for blennies due to the detrimental effects of the discharge on live barnacles. The blennies utilize empty barnacle shells as habitat. The discharge was not observed to have had any direct detrimentall effects on the crested blenny.”