Estimation of Fisheries Impacts Due to Underwater Explosives Used to Sever and Salvage Oil and Gas Platforms in the U.S. Gulf of Mexico

According to data from the National Marine Fisheries Service (NMFS) Platform Removal Observer Program which includes removals in both federal and state waters, from 1989-98 a total of 958 structures were salvaged using explosives for an annual average of roughly 96 structures . One obvious consequence of using explosives is a negative impact on fish . There has previously been no attempt to quantify the impacts of explosive platform removal on fish populations . Of special concern is the commercially and recreationally important red snapper (Lutjanus campechanus) which occurs at many of these structures . The red snapper continues to be the subject of intense government regulation as this species is severely overfished and there are significant problems in the long-term viability of the stock (Goodyear and Phares 1990 ; Goodyear 1996 ; Cowan 1998 ; Schirripa, 1998) .

Fishery managers attempt to track the size and status of stocks using mathematical equations which include variables relating to recruitment and mortality. The results of such stock assessment analyses provide managers with critical information needed to manage fisheries. This study quantifies the mortality of fish species resulting from explosive platform removals. For the first time, mortality estimates from platform removals were used in stock assessment analyses to determine the relative importance of this mortality compared with other sources of mortality such as commercial and recreational fishing, trawl bycatch, and discards. As a result, stock assessments may be improved through addition of this new parameter into stock assessment equations.

The most severely impacted fish species at explosive structure removals in order of abundance were Atlantic spadefish (Chaetodipterus faber), blue runner (Caranx crysos), red snapper (Lutjanus campechanus), and sheepshead (Archosargus probatocephalus). These four species accounted for 86% of estimated mortality. Numbers of all other impacted species were far below those of the top four. Of the species encountered in these field studies, only red snapper, gag and red drum have stock assessments conducted on them by the National Marine Fisheries Service. For red snapper, even when the mortality estimate was doubled, impacts were estimated to be small, well within the variation of our current assessments, and would not alter current determinations of status or current management recovery strategies. Similarly, current methods of assessment would not detect the even smaller changes in magnitude of gag and red drum. Results indicated no significant difference in estimated mortality of red snapper by depth, longitude, platform age, season, surface salinity, and surface temperature in the study area (14-32 m) during May to September. These analyses suggest no appropriate strata for expansion of mortality data to the greater Gulf of Mexico and indicate that platforms in the water depths studied can be included in a single group for the purpose of estimating fish mortality due to explosive platform removals. Although the effects of structure complexity on fish abundance was not an objective of this study, unpublished data from NMFS indicated structure complexity may directly influence observed mortality. This parameter was integrated into the sensitivity analysis for stock assessment . A significant difference in red snapper length at removals in 20-30 m water depths vs those at shallower and deeper depths was also incorporated into the analysis.

Three important caveats should be remembered when interpreting these results . First, species composition and abundance can change in water depths deeper than those encountered during this study . Second, sample size was small, only nine platforms out of more than 4,000 structures present in the U.S . Gulf of Mexico . Finally, all sampling was conducted during the months of May through September .

Gitschlag, G . R ., M . J . Schirripa, and J . E . Powers . 2000 .

Estimation of fisheries impacts due to underwater explosives used to sever and salvage oil and gas platforms in the U .S . Gulf of Mexico : Final report . OCS Study MMS 2000-087 .

Prepared by the National Marine Fisheries Service . U .S . Dept . of the Interior, Minerals Mgmt . Service, Gulf of Mexico OCS Region, New Orleans, LA . 80 pp .

Prepared under MMS

Interagency Agreement 17912

by

National Marine Fisheries Service

Southeast Fisheries Science Center

Miami, Florida 33149