is 50 x 50 m, these structures might provide for another 5,000 km of 

 habitat. Most of the platforms in snapper habitat are offshore of 

 Louisiana. Is it coincidence that nearly the entire nearshore gulf 

 snapper habitat except that offshore from Louisiana is considered to be 

 depressed, or do the structures, in fact, provide additional habitat 

 enabling a larger stock? 



However, there is a substantial decline of reef fish stocks in some 

 areas of the Gulf of Mexico and a known factor contributing to this 

 decline is overfishing by directed recreational and commercial users 

 (GMFMC 1980b). Other possible factors contributing to the decline are 

 destruction of habitat (natural and man-made), a large bycatch in other 

 fisheries, and large-scale environmental changes (GMFMC 1980b). An 

 insufficient data base exists to pinpoint the exact causes and magnitude 

 of the decline. Of particular importance is determining the role of 

 petroleum platforms (positive or negative) which may have either (1) 

 caused an increase in overall standing stocks of habitat- limited reef 

 fish due to increasing available habitat by about 13$; or contrastingly, 

 (2) contributed to overfishing and resulting stock declines of reef 

 fish. 



Elevated levels of trace metals have been observed in the 

 sediments, the biofouling community, and some fishes resident at 

 platforms (Tillery 1980). However, marked bioaccumulation of trace 

 metals has not been observed, at least when the elevated levels are 

 compared to background levels. The sources of elevated trace metals 

 characteristically observed in the environment in the vicinity of 

 petroleum structures likely include the structures themselves, as well 

 as the aqueous discharges emanating from some platforms. 



DRILLING FLUIDS 



The environmental fate and effects of drilling muds and cuttings 

 have long been a controversial issue. Most recently the ongoing debate 

 has culminated in a symposium conducted during January 1980- The 

 resulting publication of the proceedings was in two volumes requiring 

 1,122 pages (Ayers et al. 1980a). The following paragraphs represent 

 only a brief precis of some of the information available — all of which 

 can be found in the referenced document. 



The mechanics of drilling a well involve pumping drilling fluids 

 (mud) down the center of a rotating string of drill pipe to the drill 

 bit, where the mud exits through nozzles, picks up drill cuttings (rock 

 fragments) and returns to the surface through the annulus between the 

 drill string and the walls of the borehole and/or casings. The cuttings 

 which come out of the well bore are suspended in a large volume of 

 drilling fluids. These fluids are circulated through various mechanical 

 devices (shale shaker, sand trap, hydrocyclones and centrifuge) that 



54 



