4

Environmental Assessment of Present Removal Techniques

Explosive detonations during offshore removals may have serious adverse effects on sea turtles, marine mammals, and finfish in the vicinity of the platforms. Both marine mammals and sea turtles are protected under the Endangered Species Act, which prohibits all “take” or potential take of plants and animals designated as endangered (see Chapter 1, “Regulations, Laws, and Permits” for a definition of take). Sea turtles and several species of marine mammals are covered by this Act; all marine mammals are also protected under the Marine Mammal Protection Act.

Because of the potential damage from underwater explosions to both sea turtles and marine mammals, Section 7 of the Endangered Species Act requires that the Minerals Management Service (MMS) and the National Marine Fisheries Service (NMFS) be consulted about every explosive removal. To expedite this process, and because many removals are similar, a generic consultation was established on July 25, 1988 (Richardson, 1989).

In 1994 the Marine Mammal Protection Act (MMPA) was reauthorized. Section 101(a)(5) of the MMPA allows the secretaries of the U.S. Departments of Commerce and the Interior to authorize, in certain instances, the unintentional taking of small numbers of marine mammals by U.S. citizens incidental to activities other than commercial fishing. A new provision, Section 101(a)–(5)(D), was added in 1994 as an amendment to MMPA to streamline the authorization of incidental take of small numbers of marine mammals by “harassment.”

The harvest of fish in federal waters of the Gulf of Mexico is managed by the Gulf of Mexico Fisheries Management Council (GMFMC) under the authority of the Magnuson Fisheries Conservation and Management Act. The GMFMC implemented a Reef Fish Management Plan in November 1984, which introduced regulations designed to rebuild reef fish stocks declining because of overfishing.

HABITAT AND ECOSYSTEMS

Offshore structures provide hard-bottom habitat for a variety of marine organisms, including reef fish, sea turtles, and marine mammals. The GMFMC (1989) estimated the total natural reef habitat in the Gulf of Mexico to be approximately 15,000 square miles. One-third of this habitat lies off the coast of Louisiana and Texas, which is also where approximately 99 percent of the platforms are located. Gallaway (1981) estimated that offshore petroleum platforms provide an additional 2,000 square miles, increasing the reef fish habitat by an estimated 27 percent.

The habitat provided by offshore platforms is particularly important in the northern Gulf of Mexico, where most of the substrate is clay, silt, and sand, with little or no relief. The added habitat provided by platforms and other oil and gas-related facilities has undoubtedly affected fish populations, although these effects are not well understood (Stanley, 1994). It has been estimated that 5 to 100 times more fish occupy the area around oil and gas platforms than the neighboring areas over soft mud substrate of the Gulf of Mexico (Gerlotto et al., 1989; Stanley, 1994). Since platforms were installed, they have become important to both the recreational fishermen and the commercial fishing industry and have long been recognized as de facto artificial reefs. Artificial reef habitats have attracted an increasing number of recreational fishermen to the coastal waters of Louisiana and Texas.

From 1973 to 1993, more than 1,150 structures have been removed from the Gulf of Mexico. The loss of habitat provided by these structures may have long-term negative impacts on reef fish populations or, at a minimum, may result in the dispersal of these populations away from established fishing areas.

Many coastal states recognize the vital fish habitat of offshore platforms and have decided to try to keep these platforms in their coastal waters. In 1986, Louisiana passed legislation creating the Louisiana Artificial Reef Program which is designed to transfer ownership from participating oil and gas companies to the state through the U.S. Department of Wildlife and Fisheries. This program permits the state to share the savings from decreasing the cost of removal. The Texas legislature followed suit in 1989 with the Texas Artificial Reef Act, which directs the Texas Department of Parks and Wildlife “to actively pursue acquiring offshore platforms for use as artificial reefs in the Gulf of Mexico in deference to other structures” (Stephan et al., 1990). To date 101 platforms have been deployed as artificial reefs in the Gulf of Mexico and off the east coast of Florida, approximately 10 percent of the platforms removed from 1978 to the present.



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AN ASSESSMENT OF TECHNIQUES FOR REMOVING OFFSHORE STRUCTURES 4 Environmental Assessment of Present Removal Techniques Explosive detonations during offshore removals may have serious adverse effects on sea turtles, marine mammals, and finfish in the vicinity of the platforms. Both marine mammals and sea turtles are protected under the Endangered Species Act, which prohibits all “take” or potential take of plants and animals designated as endangered (see Chapter 1, “Regulations, Laws, and Permits” for a definition of take). Sea turtles and several species of marine mammals are covered by this Act; all marine mammals are also protected under the Marine Mammal Protection Act. Because of the potential damage from underwater explosions to both sea turtles and marine mammals, Section 7 of the Endangered Species Act requires that the Minerals Management Service (MMS) and the National Marine Fisheries Service (NMFS) be consulted about every explosive removal. To expedite this process, and because many removals are similar, a generic consultation was established on July 25, 1988 (Richardson, 1989). In 1994 the Marine Mammal Protection Act (MMPA) was reauthorized. Section 101(a)(5) of the MMPA allows the secretaries of the U.S. Departments of Commerce and the Interior to authorize, in certain instances, the unintentional taking of small numbers of marine mammals by U.S. citizens incidental to activities other than commercial fishing. A new provision, Section 101(a)–(5)(D), was added in 1994 as an amendment to MMPA to streamline the authorization of incidental take of small numbers of marine mammals by “harassment.” The harvest of fish in federal waters of the Gulf of Mexico is managed by the Gulf of Mexico Fisheries Management Council (GMFMC) under the authority of the Magnuson Fisheries Conservation and Management Act. The GMFMC implemented a Reef Fish Management Plan in November 1984, which introduced regulations designed to rebuild reef fish stocks declining because of overfishing. HABITAT AND ECOSYSTEMS Offshore structures provide hard-bottom habitat for a variety of marine organisms, including reef fish, sea turtles, and marine mammals. The GMFMC (1989) estimated the total natural reef habitat in the Gulf of Mexico to be approximately 15,000 square miles. One-third of this habitat lies off the coast of Louisiana and Texas, which is also where approximately 99 percent of the platforms are located. Gallaway (1981) estimated that offshore petroleum platforms provide an additional 2,000 square miles, increasing the reef fish habitat by an estimated 27 percent. The habitat provided by offshore platforms is particularly important in the northern Gulf of Mexico, where most of the substrate is clay, silt, and sand, with little or no relief. The added habitat provided by platforms and other oil and gas-related facilities has undoubtedly affected fish populations, although these effects are not well understood (Stanley, 1994). It has been estimated that 5 to 100 times more fish occupy the area around oil and gas platforms than the neighboring areas over soft mud substrate of the Gulf of Mexico (Gerlotto et al., 1989; Stanley, 1994). Since platforms were installed, they have become important to both the recreational fishermen and the commercial fishing industry and have long been recognized as de facto artificial reefs. Artificial reef habitats have attracted an increasing number of recreational fishermen to the coastal waters of Louisiana and Texas. From 1973 to 1993, more than 1,150 structures have been removed from the Gulf of Mexico. The loss of habitat provided by these structures may have long-term negative impacts on reef fish populations or, at a minimum, may result in the dispersal of these populations away from established fishing areas. Many coastal states recognize the vital fish habitat of offshore platforms and have decided to try to keep these platforms in their coastal waters. In 1986, Louisiana passed legislation creating the Louisiana Artificial Reef Program which is designed to transfer ownership from participating oil and gas companies to the state through the U.S. Department of Wildlife and Fisheries. This program permits the state to share the savings from decreasing the cost of removal. The Texas legislature followed suit in 1989 with the Texas Artificial Reef Act, which directs the Texas Department of Parks and Wildlife “to actively pursue acquiring offshore platforms for use as artificial reefs in the Gulf of Mexico in deference to other structures” (Stephan et al., 1990). To date 101 platforms have been deployed as artificial reefs in the Gulf of Mexico and off the east coast of Florida, approximately 10 percent of the platforms removed from 1978 to the present.

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AN ASSESSMENT OF TECHNIQUES FOR REMOVING OFFSHORE STRUCTURES Sea Turtles Sea turtles have been observed in the vicinity of offshore platforms. The loggerhead turtle is the most common species sighted around oil platforms (Hastings et al., 1976; Rosman et al., 1987), but leatherback, green turtles, Kemp's ridley and hawksbill have also been observed (Fuller and Tappan, 1986; Gitschlag and Renaud, 1989; Gitschlag and Herczeg, 1994). Loggerheads may reside at specific offshore structures for long periods of time (Rosman et al., 1987; Gitschlag and Renaud, 1989). The probability of occupation by sea turtles increases with the age of the structure (Rosman et al., 1987). Sea turtles probably use oil platforms as places to feed and rest. They habitually sleep next to or under hard structures— usually rock outcroppings or reefs (Ogden et al., 1983; Wershoven and Wershoven, 1989). Offshore structures afford refuge from predators and stability in water currents, and loggerheads have been seen sleeping under platforms or next to support structures (Hastings et al., 1976; Rosman et al., 1987; Gitschlag and Renaud, 1989; Gitschlag, 1990; Renaud and Carpenter, 1994). The potential for damage to sea turtles from the explosive removal of offshore structures first became apparent in March and April of 1986 when 51 dead sea turtles, primarily Kemp's ridleys, washed ashore on Texas beaches after the removal of platforms in state waters that involved 22 underwater explosions. Because shrimp fishing (another cause of sea turtle mortality) was at a very low level in the area, the explosions were identified as the probable cause (Klima et al., 1988), although this was never verified. A short time later, 11 sightings of sea turtles were reported at a platform prior to an explosive removal. Two programs to evaluate the association of sea turtles with platforms were planned by NMFS: aerial surveys in the north-central Gulf of Mexico and an observer program during explosive removals. Aerial surveys were conducted in seven survey areas off the coast of Louisiana from June 1988 to June 1990 (Lohoefener et al., 1989, 1990). Two of the survey areas were near the Chandeleur and Breton islands; the other five were west of the Mississippi River. The number of platforms in each area varied from 40 to 155. In the study areas near the Chandeleur and Breton islands, sea turtles were positively associated with platforms. That is, there were significantly more turtles near platforms than there would be by random distribution. In 1987 the NMFS initiated a sea turtle observer program at all explosive removal sites of oil and gas structures in state and federal waters of the Gulf of Mexico (Gitschlag, 1990). For at least 48 hours prior to detonation, NMFS observers watch for sea turtles from the surface. Helicopter aerial surveys within a mile radius of the removal site are conducted 30 minutes prior to and after detonation (Gitschlag and Herczeg, 1994). If sea turtles are observed, detonations are delayed until the sea turtles have been safely removed or have left the area. From March 1987 through the end of 1988, 108 structures were removed; there were 36 sea turtles sighted at 13 percent of the structures (Gitschlag and Renaud, 1989). In 1992 NMFS observers conducted 6,500 hours of monitoring at 106 structure removals; turtles were observed at 20 percent of the removal sites (Gitschlag and Herczeg, 1994). Official NMFS observers recorded 45 sightings of 18 individual sea turtles. Twenty-seven turtles were observed (some by individuals who were not NMFS employees) in 61 sightings. The observation rate for aerial surveys was nearly 30 times greater than surface surveys. The concentration of sea turtles around offshore platforms can be quite high. During 30 hours of surface observations at a platform approximately 30 miles off the coast of Galveston, Texas, there were 170 sightings of sea turtles. Over a period of 10 days, at least 11 individual loggerheads were identified (Gitschlag, 1990). There are only a few estimates of turtle abundance and turtle mortality because turtles can be difficult to observe, and turtles killed by explosions may not float to the surface until sufficient bacterial activity has occurred, which takes several days (NRC, 1990). In addition, nonlethal damage from the explosions or delayed lethal effects—both of which may have a greater impact on sea turtle populations than immediate death from explosions—are not apparent to observers. Plans for long-term management have been developed to ensure the recovery of sea turtle populations in U.S. waters (e.g., NMFS and USFWS, 1991; USFWS and NMFS, 1992). If these efforts are successful and turtle populations increase, the numbers of sea turtles near platforms—and thus the risk from explosive removals—will also increase. To document the effects of underwater explosions on sea turtles, the NMF undertook an experiment to determine the extent of injuries to sea turtles placed at 750 feet, 1,200 feet, 1,800 feet, and 3,000 feet from an explosive removal of an oil platform (Klima et al., 1988). On June 21, 1986, a platform in 30 feet of water was removed by detonating 50 pounds of nitro-methane inside each of four jacket legs 15 feet below mudline. A pressure of 1 by 106 psi was produced at the point of detonation (Duronslet et al., 1986). One Kemp's ridley and one loggerhead were placed in a cage at each of the four distances. Just before the detonation, the cages were lowered to a mid-water depth of 15 feet. The cages were retrieved shortly after detonation. The four turtles within 1,200 feet of the explosion were unconscious, as was the loggerhead in the cage at 3,000 feet. If they had been left in the water these turtles may have drowned. Turtles in all of the cages were affected. Some suffered everted cloaca and vasodilation, which lasted for two to three weeks. Two observations of sea turtles severely wounded by explosive removals of platforms have been made. A dead or injured turtle drifting about 10 feet below the surface was

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AN ASSESSMENT OF TECHNIQUES FOR REMOVING OFFSHORE STRUCTURES sighted 1.5 hours after the explosive removal of a structure in 1986 (Gitschlag and Renaud, 1989). At the removal site of a caisson in 1991, within one minute of detonation, a loggerhead with a fracture down the length of its carapace surfaced (Gitschlag, 1995). The turtle was 15 to 100 feet from the detonation site. Two immature green turtles (100 to 150 feet away) were killed when 20 pounds of plastic explosives (C-4) were detonated in open water by a U.S. Navy Ordnance Disposal Team. Necropsies revealed extensive internal damage, particularly to the lungs (Schroeder, 1995). Three sea turtles were unintentionally exposed to underwater shock tests by the Naval Coastal Systems Center in 1981 off the coast of Panama City, Florida. Three detonations of 1,200 pounds of TNT at mid-depth (in about 120 feet of water) injured one turtle at a distance of 500 to 700 feet and another at 1,200 feet. A third turtle at 2,000 feet was apparently not injured (O'Keeffe and Young, 1984; Klima et al., 1988). The Committee on Sea Turtle Conservation of the National Research Council (NRC, 1990) estimated that between 8 and 50 turtles have been killed each year from the explosive removal of oil platforms. The committee report cautioned that this estimate may not be accurate. On the one hand, the estimate may be low because it is based on data from aerial surveys; on the other hand, it may be high because it does not include the effect of mitigation measures now required by NMFS. The 1990 report concluded that the data on the association of sea turtles with platforms and the effects of explosive removals on sea turtles are inadequate and that further research is needed. Marine Mammals Dolphins have been observed around platforms, especially in water deeper than 450 feet; and 28 species of cetaceans have been documented in the Gulf of Mexico, most of which are deep-water species (Mullin et al., 1990; Davis et al., 1995). This includes endangered sperm whales, which have been observed within sight of deep-water platforms off the coast of Louisiana. An extensive survey of the distribution and abundance of cetaceans in the north-central and western Gulf of Mexico was conducted in 1992 and 1993. In the survey, conducted quarterly by Texas A&M University and NMFS and sponsored by the MMS, 21 species of cetaceans were identified in the area mentioned above (Davis et al., 1995). The most common species, except for bottlenose dolphins, sighted during these quarterly surveys were sperm whales and pantropical spotted dolphins. At least 25 species of cetaceans are permanent or transient residents in the entire Gulf of Mexico. Bottlenose dolphins are found throughout the area from the bays and estuaries to waters more than 1,640 deep. Atlantic spotted dolphins are also present in shelf waters 260 to 650 feet deep. Sperm whales have been observed in the Gulf of Mexico from water depths of 340 feet to more than 6,500 feet (Collum and Fritts, 1985). Pantropical dolphins are found along the continental slope in the north-central and western Gulf of Mexico and have been spotted in and around some deeper water production platforms (650 feet or more). It is possible that animals of any or all of these species could be found near deeper offshore oil and gas platforms at one time or another. In the future, as platforms are located in deeper water, the risks to these species could increase. The species most likely to be near shallow-water platforms, which are usually older and, therefore, candidates for explosive removal, are bottlenose dolphins and Atlantic spotted dolphins. Bottlenose dolphins have been found around platforms in as little as a few feet of water. Atlantic spotted dolphins are found over the slope in depths of 600 feet and deeper, and sperm whales, although observed at depths of 340 feet and more, prefer depths more than 3,000 feet (Davis et al., 1995). Forty-one dead dolphins (40 bottlenose dolphins and 1 Atlantic spotted dolphin) found on Texas beaches in March and April 1986 may have been associated with the removal of platforms in state waters that involved 22 underwater explosions (Klima et al., 1988). There are also many reports of stranded cetaceans in the gulf after hurricanes or other large oceanic storms. But evidence from the necropsies has not revealed explosive-impact-type injuries. In 1987 and 1988, 740 bottlenose dolphins were stranded along the Atlantic coast from New Jersey to Florida and in the Gulf of Mexico from Alabama to Texas. Unfortunately, most of the stranded mammals were in an advanced state of decomposition that the cause of death was difficult if not impossible to ascertain. Biotoxins were implicated as the cause of death in the animals that could be examined (Geraci, 1989). There was speculation that some animals had been injured by explosive impact from seismic or other outer continental shelf activities, but no evidence was reported from necropsies. No direct scientific evidence of physical damage from exposure to high noise levels exists, but baleen whales, sperm whales, and several species of dolphins have exhibited disturbance reactions, such as cessation of feeding, changes in respiration and diving patterns, and avoidance behavior (ARPA, 1995). The sound reception and production capabilities of many suborders and families of marine mammals are well known. And every group of cetaceans studied has been found to be affected by high-level noise, including every species thought to be present in the Gulf of Mexico. Although the current procedures in place to protect endangered sea turtles from high noise levels provide some protection, peak levels of exposure calculated during tests on sea turtles in 1986 (213 decibels (dB) reference (re:)

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AN ASSESSMENT OF TECHNIQUES FOR REMOVING OFFSHORE STRUCTURES 1 micropascal (μPa)* at 1,200 to 1,800 feet), which many scientists feel are potentially damaging to the hearing mechanism of marine mammals (Malme et al., 1983; Richardson et al., 1986; NRC, 1994). However, there is no scientific evidence that the minor and short-term behavioral reactions observed indicate any significant or long-term effects. For example, bottlenose dolphins observed 1,950 feet from the platform to be removed by explosives during the 1986 sea turtle exposure test mentioned above, swam rapidly away at detonation. They were reportedly exposed to a calculated peak of 213 dB re: 1 μPa at 1,200 to 1,800 feet. Unfortunately, measured levels and data on the acoustic spectra of the explosion are not available. In response to a request by the American Petroleum Institute for a small-take authorization, NMFS proposed a new rule, which is currently under consideration. The rule authorizes the incidental take of bottlenose dolphins and Atlantic spotted dolphins. The rule specifies that explosives can be used only during daylight hours, unless authorized by the on-site representative of NMFS or MMS, and only after it has been determined that there are no dolphins within 3,000 feet of the structure. This distance was selected on the basis of a computer model that predicted that a dolphin calf would be only slightly injured from a 1,200 pound charge detonated in open water at 4,000 feet. In most instances under current practice, charges are limited to 50 pounds and are placed at least 15 feet below the mudline. NMFS assumed, based on the effects of a 1,200-pound charge at 4,000 feet, that a 3,000-foot safety zone would ensure that dolphins would not be injured. It is not clear what assumptions were made about environmental or oceanographic conditions, water depth, or bottom type. The Marine Mammal Commission, in a 1994 report to Congress (MMC, 1994), voiced the same concerns about potential harm to marine mammals from explosive removal operations and recommended that acoustic monitoring around platforms scheduled for removal by explosive means would be useful for assessing the presence or absence of dolphins and whales and potential exposure to high-level noise. The commission also recommended that permit requests include all species of marine mammals that could be affected. Based on recent surveys, these would include bottlenose dolphins, Atlantic spotted dolphins, pantropical spotted dolphins, and sperm whales (Collum and Fritts, 1985). Existing data indicate that the current NMFS Observer Program has been successful in preventing injuries and deaths of turtles and marine mammals from explosive removals. Fish Oil and gas platforms provide significant habitat for Gulf of Mexico reef fishes and have become the preferred destination for many fishermen. Witzig (1986) estimated that 70 percent of all saltwater fishing trips in the exclusive economic zone (more than 3 miles from shore) off Louisiana were destined for one or more of the offshore oil and gas structures. Furthermore, it was determined that anglers who fish around platforms catch bigger, more desirable fish than those who fish in other areas (Reggio, 1987). In fact, they had the highest catch rates of all recreational fishers in the United States (Stanley and Wilson, 1990). Avanti, Inc. (1991), using data from the Marine Recreational Fisheries Statistical Survey, estimated that 30 percent of the 15 million fish caught off the coast of Louisiana and Texas by recreational fishers were caught near platforms. Dimitroff (1982) conservatively estimated that a group of 112 commercial snapper and grouper fishers from the Florida panhandle who regularly fish at petroleum platforms off the coast of Louisiana and Texas catch approximately 450,000 pounds of reef fish annually valued at approximately $2 million. Although these figures are impressive, there is little documentation as to whether oil and gas platforms increase fish populations or just redistribute them. There are many reasons for the lack of information: the difficulty of sampling with traditional sampling gear; limited visibility; the tendency of fish to avoid divers; and the lack of standard survey techniques. Despite these difficulties, however, investigators have found that the number of fish around platforms ranges from a few hundred to thousands, depending on platform size, location, and the time of the survey (Continental Shelf Associates, 1982; Putt, 1982; Stanley and Wilson, 1991). One study (Gerlotto et al., 1989) found that fish densities were 5 to 50 times higher immediately adjacent to platforms than they were 500 feet away. Stanley (1994) estimated the region of influence around a platform to be about 50 feet. Fish densities were 10 to 100 times higher within this area than on adjacent soft substrate. In a study conducted between September 1990 and June 1992, the fish population at a platform in 72 feet of water ranged from 1,990 to 28,100 fish, with an average of 12,600 fish; 2,644 (±689) red snappers per month were found at the site (Stanley, 1994). The GMFMC (Gulf of Mexico Fisheries Management Council) became concerned about the effect of platform removals on reef fish populations of commercial and recreational value, particularly the number of fish killed by explosives. NMFS began evaluating the impact of explosive removals on fish in conjunction with the sea turtle observer program by collecting and counting dead fish floating on the surface. From 1986 through 1994, they monitored 751 removals involving explosives —513 platforms, 185 caissons, 47 submerged wells, and 6 flare piles. To enhance *Seismic exploration devices produce peak levels of 212 to 230 dB re: 1 μPa at one meter (Johnston and Cain, 1981; Holiday et al., 1984).

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AN ASSESSMENT OF TECHNIQUES FOR REMOVING OFFSHORE STRUCTURES our understanding of the long-term effects of removals on fish population dynamics, this information needs to be supplemented with statistically valid data of the number of fishboth sinkers and floaterskilled during removal operations (Gitschlag, 1995). A study assessing the fish kill at explosive platform removals is currently being conducted by NMFS with funding from MMS. As of April 1995, three platforms had been studied at water depths of 45, 55, and 82 feet. Results from this small sample may not be representative, and use of the preliminary data is inappropriate at this time. Nevertheless, some general conclusions may be drawn. The vast majority of the estimated fish kill within a radius of 330 feet of a platform occurs within 80 to 100 feet of the structure (Gitschlag, 1995). Most fish at a platform in 72 feet of water were within approximately 50 feet of the platform. Based on preliminary data, the species most affected by the explosive removals monitored by NMFS were Atlantic spadefish, sheepshead, red snapper, and blue runner. These are the same species found around platforms at similar depths described by Gallaway and Lewbel (1982) and Stanley (1994). Standard explosive removal procedures would kill most of the fish near a platform at the time of detonation. Stanley (1994) estimated the number of fish around an 8-pile platform in 72 feet of water ranged from 1,990 to 28,100 fish over a period of 18 months (figure 4-1). The mean, or maximum, density (plus or minus one standard deviation or standard error), of red snapper around the platform was 2,644 (±699) per month. Higher densities of red snapper could be expected in deeper water (Gitschlag, 1995). Although the number of certain fish of overexploited species (e.g., red snapper) impacted by explosive structure removals is economically insignificant compared with the take by commercial fisheries, the by-catch of shrimp fisheries and recreational fisheries, the long-term biological effects could be significant. Fish killed during explosive removals FIGURE 4-1 Number of fish at Platform WC 352. Source: Stanley (1994). can be counted and therefore accounted for when estimating population levels. Fish that die later from the effects of an explosion are not counted, although this additional loss, depending on the numbers and the age of the fish killed, could have a significant impact on population dynamics as well as unfortunate ecological and economic implications. Reef fish are managed as a multispecies complex. The combined snapper and grouper complex accounted for $38.7 million of the total value of fish for Gulf of Mexico commercial fishing. Some 3.3 million recreational fisherman fishing the Gulf of Mexico in 1993 caught about 5 million red snapper (Newlin, 1993). Snappers, which constitute a large percentage of the fish around offshore platforms, are obviously a major commercial and recreational resource in the Gulf of Mexico. The long-term effects of destroying a component of the reef fish complex are being studied but are still not well understood. Just as the number of fish at a single platform may vary dramatically from month to month (see figure 4-1), the species composition may also vary from platform to platform. Factors affecting these variations may include the water depth, age, size, geographic location, seasonal variations, how accessible a platform is to recreational and commercial fishermen, and water quality (Gallaway, 1981; Gallaway and Lewbel, 1982; Stanley, 1994). Although reef species around platforms were once thought to be relatively stable (Gallaway, 1981), movement to and from platforms is now more apparent (Stanley, 1994). Therefore, it is difficult to develop estimates of the potential impact of explosive removals on fish considering the wide range of structures in the Gulf of Mexico, although some estimates of species composition and abundance can be made. To facilitate research on the effects of explosive removals on fish populations, a useful experiment would be to measure the blast wave characteristics (pressures, frequencies, and attenuation) at varying distances from the platform to create a database. The platform should be in relatively deep water with a typical soft bottom. Special attention should be given to the mitigation of explosive effects by reducing the charge weight (including shaped and specially configured charges) and the effect of burial depth. In concert with the blast wave measurements, probability of kill data should be obtained for the fish species of prime interest in cages judiciously placed at varying distances from the blast. Appropriately deployed bubble curtains can attenuate and refract the blast pressure of detonations; obviously, they require that the fish be expelled from inside the curtain surrounding the platform (e.g., by the acoustic means discussed earlier). Data on the effectiveness of bubble curtains are sketchy so far and limited to shallow water. The distance from the platform for a bubble curtain to reduce blast pressure to acceptable levels has not been determined; nor has the path of the blast wave through the sea bottom under the curtain. Using bubble curtains would also pose significant

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AN ASSESSMENT OF TECHNIQUES FOR REMOVING OFFSHORE STRUCTURES deployment problems and may not be very beneficial. Bubble curtains and other mitigating techniques are discussed in detail in chapter 2. NONLETHAL EFFECTS OF EXPLOSIVE REMOVALS According to Fish and Mobray (1970), a significant number of finfish species and several crustaceans can produce sound. Some of these species, including the snapper and grouper group, are found near platforms. Many also have reasonable hearing sensitivity, especially at low frequencies. In some species only males are soniferous, and then only seasonally. In others, both sexes produce sound. Also, many of these species have specialized hearing organs and special sound-producing muscles associated with an air bladder. Although it is assumed that sound is behaviorally significant to this group of fishes, little or no field work has been done on the potential damage from high-level noise from shipping, explosive removals, acoustic tomographic studies, and seismic and other industrial activities. Sound pressure levels comparable to the levels from explosives have lethal effects on fish near the platform. Based on preliminary data, the dominant species impacted by explosive removals are Atlantic spadefish, red snapper, sheepshead, and blue runner. Long-term, sublethal effects (e.g., temporary or permanent hearing loss and other physiological and neurological damage) on future reproductive performance and predator avoidance are not known. If fish found around platforms represent specific year classes, or are important components of the reef ecosystem as predators or competitors, the damage could be significant. The effects of high levels of sound incidental to industrial development on finfishes in the Gulf of Mexico are not known, although reactions of fish to infrasound have been studied (Enger et al., 1993). Unfortunately, neurophysiological pathology studies in fishes exposed to explosive removals have not been conducted. SUMMARY Current data on the deaths of or injuries to sea turtles and marine mammals from explosive removals indicate that the existing NMFS Observer Progam has been successful in limiting mitigating damage to these species from explosive removals. According to NMFS observers, the currently required 48-hour observation period could be shortened to 24 hours without decreasing the benefits and with some savings in cost. The effects of explosive removals on fish are substantial. But more systematic research is needed to determine if the number of fish killed will have long-term effects on population dynamics for certain fish species. Concerns about the potential effects of the loss of habitat once platforms are removed must also be addressed. REFERENCES ARPA (Advanced Research Projects Agency). 1995. Final Environmental Impact Statement/Environmental Impact Report for the California Acoustic Thermometry of Ocean Climate Project and Associated Marine Mammal Research Program, vol. 1. Arlington, Va.: ARPA. Avanti, Inc. 1991. Environmental Assessment for the Regulatory Impact Analysis of the Offshore Oil and Gas Extraction Industry Proposed Effluent Guidelines. Vol. 1: Modeled Impacts. EPA Contract No. 68-C8-0015. Collum, L.A., and T.H. Fritts. 1985. Sperm whales (Physeter catodon) in the Gulf of Mexico. Southwestern Naturalist . Continental Shelf Associates. 1982. Study of the effect of oil and gas activities on reef fish populations in the Gulf of Mexico OCS area. OCS Report No. MMS 82–10. U.S. Department of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, Louisiana. Davis, R.W., B. Wursig, W. Evans, G. Fargion, R. Benson, J. Norris, and T. Jefferson . 1995. Distribution and Abundance of Marine Mammals in the North–Central and Western Gulf of Mexico: Draft Final Report, vol. 2, Technical Report. OCS Study No. MMS. Prepared by the Texas Institute of Oceanography and the National Marine Fisheries Service.U.S. Department of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, Louisiana. Dimitroff, F. 1982. Survey of snapper and grouper fishermen off northwest Florida coast . Pp. 86–114 in Proceedings of 3rd Annual Gulf of Mexico Information Transfer Meeting . U.S. Department of the Interior, Minerals Management Service, New Orleans, Louisiana. Duronslet, M.J., C.W. Caillouet, S. Manzella, K.W. Indelicato, C.T. Fontaine, D.B. Revera, T. Williams, and D. Boss. 1986. The Effects of an Underwater Explosion on the Sea Turtles Lepidochelys kempi and Caretta caretta with Observations of Effects on Other Marine Organisms. 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