Ecological effects of energy development on reef fish of the Flower Garden Banks

Abstract

From the Abstract: “Research cruises were conducted at the Flower Garden Banks in the northwestern Gulf of Mexico over the period 1980 to 1982 as part of a study designed to evaluate the effects of operations of a drilling platform (Mobil HI-A389-A) adjacent to the East Flower Garden Bank on reef fish populations. The platform was not installed until early fall of 1981.

The first two cruises were undertaken during fall and winter of 1980 and were largely for (1) reconnaissance surveys of each bank and a drilling platform (Mobil HI-A595-D) which, although 9 nautical miles west of the banks, was the closest of any active drilling structure, and (2) development and refinement of underwater research techniques. During spring and summer of 1981 (Cruises 3 and 4) quantitative surveys were conducted at each bank and at the platform. Based upon the results of these surveys, it became obvious that sample sizes would have to be considerably increased in order to obtain the requisite levels of accuracy and precision necessary to be able to detect any effects on fish population levels following installation of the platform adjacent to the banks.

The platform was installed adjacent to the East Flower Garden Bank shortly before Cruise 5, and fish population sampling effort was focused around this bank and the platform for the balance of Cruises 5–8. Data from these cruises were representative of fall 1981, and spring, summer and fall of 1982, respectively. The Flower Garden Banks were found to have characteristic fish assemblages, primarily zoned by depth and/or habitat types. Each of these habitat types were mapped to determine total area and fish densities were determined based upon a total of 357 h of samples with the data recorded by 1-min intervals. Using maximum likelihood estimation procedures, seasonal standing stocks were estimated for each of 16 reef fish taxa.

Confidence limits were also calculated for these standing stock estimates within each major habitat type. The creole fish, a serranid, was the most abundant fish on the East Flower Garden Bank, having populations estimated to range from over 400,000 to some 993,948 individuals. Red snapper were much less abundant (4,000 to 20,000) and population levels of myeteropercid groupers, also commercially fished, ranged between 20,000 and 47,000 individuals. In general, all of the reef fish species having the highest population levels were plankton feeding forms.

Based upon the abundance levels of fishes before and during drilling activities, and analysis of spatial abundance patterns of fish vis-a-vis  the platform, the bottom-water discharge of drill muds and cuttings during 1982 did not result in any measurable impacts on the spatial densitypatterns or overall population levels of reef fish. One of the most significant overall effects of the installation of the Mobil Platform HIA389- A in proximity to the East Flower Garden Bank was its colonization by a diverse community of epibiota and fishes where none existed before.”