ACCESS NUMBER: 17912 

STUDY TITLE: Estimation of Fisheries Impacts Due to Underwater Explosions Used to 

Sever and Salvage Petroleum Platforms 

REPORT TITLE: Estimation of Fisheries Impacts Due to Underwater Explosives Used 

to Sever and Salvage Oil and Gas Platforms 

CONTRACT NUMBER: IA-17912 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREAS: Eastern, Central, and Western 

FISCAL YEARS OF PROJECT FUNDING: 1992; 1993; 1995; 1996; 1997 

COMPLETION DATE OF REPORT: 2000 

COSTS: FY 1992: $250,000; FY 1993: $516,000; FY 1995: $135,000; FY 1996: 

$246,300; FY 1997: $446,600; CUMULATIVE PROJECT COSTS: $1,593,900 

PROJECT MANAGER: B. Brown 

AFFILIATION: National Marine Fisheries Service, Southeast Fisheries Science Center 

ADDRESS: 75 Virginia Beach Drive, Miami, Florida 33149 

PRINCIPAL INVESTIGATOR*

: G. Gitschlag 

KEY WORDS: Gulf of Mexico; fisheries; platform removal; biological impacts; mortality 

estimates; fish tagging; population estimates; transect surveys; stock assessment: red 

snapper. 

BACKGROUND: As of January 31, 2000 there were 3,967 oil and gas structures 

present in federal waters of the Gulf of Mexico. Federal regulations require removal of 

these structures within one year of lease termination. From 1989-98 nearly 1,000 

structures were salvaged in both federal and state waters using explosives. In the most 

common explosive removal method, 40-50 lb charges are detonated inside the pilings 

and well conductors at a minimum depth of 5 m below the sea floor (MMS requirement). 

 Consequently, hundreds of pounds of explosives, primarily Comp-B and C-4, are often 

used at offshore platform removals. Since offshore platforms function as artificial reefs 

attracting a wide variety of marine life, one obvious consequence of explosive structure 

removal is a negative impact on fish. Although offshore platforms have been the 

subject of much scientific study over the years, 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 
ACCESS NUMBER: 17912 

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. 

OBJECTIVES: (1) Determine the abundance of fish populations, fish mortality resulting 

from explosives use, and other factors contributing to the mortality of fish populations at 

sampled platform removal sites; (2) Estimate the total at-risk population abundance and 

potential mortality from explosive platform removal in the Gulf of Mexico as well as the 

effects on fish stock productivity for those populations (with special emphasis on red 

snapper); compare this to other anthropogenic sources of mortality; statistically evaluate 

strategies for mitigating the impact of removal on at-risk fish populations in terms of their 

short and long term reproductive potential. 

DESCRIPTION: Sampling sites included ten platforms extending from the upper Texas 

coast to the Mississippi River. Data collection allowed estimates of total fish mortality at 

nine of ten sites. Prior to detonation of explosives, fish were captured, tagged and 

released alive. After explosives were detonated, dead fish floating on the surface were 

collected from inflatable boats using dip nets. Divers manually sampled dead fish that 

sank to the sea floor using transect lines, circular surveys, and sampling frames. Dives 

were delayed a minimum of 30 minutes after detonation to allow fish to die and sink to 

the bottom. Transect lines radiating out from the platform provided continuity of 

sampling generally to a distance of 100 m. Circular surveys measuring 6.7 m in 

diameter produced discrete samples around the platform. Sampling frames of various 

dimensions were used to collect dead fish on the sea floor beneath the platform. Fish 

were identified, weighed, measured, and checked for tag presence. Pre-detonation fish 

populations were estimated for tagged species by equating the ratios of tagged to total 

fish present before detonations with the ratio of tagged to total fish present in samples 

collected after detonations and solving for the unknown parameter. Mortality of fish that 

sank to the sea floor was estimated by multiplying fish density from samples by sea 

floor area. Addition of mortalities collected at the surface provided an estimate of total 

mortality. Using the mean number of red snapper killed per platform, total mortality of 

red snapper resulting from all explosive structure removals in the U.S. Gulf of Mexico 

was calculated. Results were used in stock assessment analyses to determine the 

relative contribution of mortality from explosive structure removals with other 

anthropogenic sources of mortality. 

SIGNIFICANT CONCLUSIONS: 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. 
ACCESS NUMBER: 17912 

Similarly, current methods of assessment would not detect the even smaller changes in 

magnitude of gag and red drum. 

STUDY RESULTS: Mean red snapper mortality was 515 fish per platform based on 

sampling conducted at nine study sites from 1993-1999 during May-September in water 

depths of 14-32 m. Results indicated no significant difference in estimated mortality of 

red snapper by water depth, longitude, platform age, season, surface salinity, and 

surface temperature. If a wider range of water depths, seasons, etc. were studied, 

some of these analyses would undoubtedly have shown a significant difference. Red 

snapper population estimates at seven platforms ranged from 503-1943 with a mean of 

905. Fish density for all species combined decreased with increasing distance from the 

platform. Significant differences in fish density occurred between 0-7 and 18-25 m as 

well as between 0-25 and 25-50 m samples. Results refer to fish greater than or equal 

to 8 cm in total length. 

STUDY PRODUCTS: Gitschlag, G. R., M. J. Schirripa, and J. E. Powers. 2001. 

Estimation of fisheries impacts due to underwater explosives used to sever and salvage 

oil and gas platforms in the U.S. Gulf of Mexico. A final report prepared by the National 

Marine Fisheries Service for the U.S. Department of the Interior, Minerals Management 

Service, Gulf of Mexico OCS Region, New Orleans, LA. Contract No. IA-17912. OCS 

Study MMS 2000-87 94p. 

*

P.I.'s affiliation may be different than that listed for Project Manager(s).