By Frank Hamm, Regina Rudolph, and Megan Thompson

Oil spills occur frequently in the United States. An example that has greatly impacted communities of marine mammals and other wildlife was the Exxon Valdez Oil spill. It happened on March 1989 in the Prince William Sound, Alaska. An Exxon oil tanker was about to reach its port when it struck Bligh reef, spilling approximately 11 million gallons of North Slope crude oil into the sound. It occurred while the drunken captain was below decks and an uncertified third mate at the helm (McAlpine 1999). The oil quickly spread over 1100 miles of Alaskan coastlines in a matter of days.

An oil spill response was most effective before the oil had a chance to invade shorelines. Unfortunately, the cleanup did not start immediately due to failing, inadequate machinery and disruptive storms (McAlpine 1999). As the restoration project began, Exxon used several methods to remove the oil. An important method called boom, which could be used as a deflection device, barrier; a corral for contained oil or used in another method such as burning. It works at the water’s surface and just below the surface (Piper 1993). Burning the oil off the surface of the water was often useful, but had to be monitored carefully. The best time for this method was between 12-72 hours following the spill (Piper 1993). This method was not very successful due to the fact that the oil lay on the water for over three days. Skimming the surface mechanically was useful with the high pressure/hot water method. This method forced the oil off the shorelines and into a boom and then skimmed off the water’s surface. If this were not done systematically, called uncoordinated spraying, then treatment would be uneven, producing places that were not clean within the sites being treated (Piper 1993). Chemical cleaners, solvents and dispersants may be effective depending on the location in which it was used. Corexit 9580M2 manufactured by Exxon was used in the cleaning process. This chemical was produced from Kerosene with its aromatic properties removed, and detergents were added (Piper 1993). Dispersants were designed to break up large concentrations of oil into smaller concentrations. Combined with the use of bioremediation, which was the method of using fertilizers and oil eating bacteria to breakdown the pollutants, was very useful (Piper 1993). All of these methods were beneficial to some extent.

The population of Stellar Sea Lions has been declining from southern and central California, the Gulf of Alaska, the Aleutian Islands, the central Bering Sea and Russia since the 1970’s (Calkins et al., 1994). Populations in the United States have declined approximately 75% over the past 20+ years (Calkins et al., 1999). The declines detected in 1989 led to listing Stellar Sea Lions as threatened under the Endangered Species Act and also as depleted under the Marine Mammal Protection Act in November 1990 (Calkins et al., 1994).

The oil from the Exxon Valdez oil spill did not linger on sea lion rookeries or haulouts, most likely because of the steep slopes and also high surf activity. Therefore, they did not lie in pools of oil while hauled out. Lesions were found in the brain tissues of adults and juveniles, as well as in most other organ systems. Although these lesions were present in sea lions, no significant impact on the population due to the oil spill could be found. The previous population declines did continue (Calkins et al., 1994).

The Exxon Valdez oil spill effected some of the largest harbor seal haulout sites in Prince William Sound (Frost et al., 1994). Between 1984 and 1988, annual populations declined 11% at oiled sites, and 13% at unoiled sites; between 1988 and 1989, the decline at oiled sites increased to 43% (Frost et al., 1994). In the weeks following the Exxon spill, harbor seals, known for being difficult to approach, were easily approachable, behaved oddly, were reported as being sick, lethargic, and unusually tame (Lowry and Frost, 1993).

When brain tissue samples were microscopically examined, lesions were found. These lesions were mostly found in the thalamus, which would have caused simple tasks such as swimming, breathing, diving and feeding very difficult (Frost, 1997). The area of the brain responsible for sensing the environment was also effected, which may have caused thermoregulatory problems (Lowry et al., 1994). The overall molting counts of harbor seals have stabilized, but since 1989 the pupping counts have continued to decline (Lowry and Frost, 1993). The number of harbor seals in Prince William Sound had not met the recovery objective of the Exxon Trustee Council as of 1997 (Frost et al., 1999).

There are two types of pods in Prince William Sound, residents and transients. Residents are usually observed in large pods, have a smaller home range and are more easily approached than transients (Dahlheim and Wright, 1993). This report will focus on the effects of the Exxon Valdez oil spill on a resident pod known as the AB pod. The AB pod was effected the most by the Exxon oil spill. In September 1988, the AB pod had 36 members (Matkin et al., 1994). On March 31, 1989 only 29 whales were counted in the pod. Of these seven missing whales, three were adult females and four were juveniles (Restoration Notebook). An additional six whales were missing in 1990, and one more was missing in 1991.

The natural mortality rate for killer whales is 2.2% or less (Dahlheim, 1994). The 1988-89 mortality rate for the AB pod was 19.4%; the 1989-90 rate was 20.7% (Dahlheim and Wright, 1993). The oil spill also caused physiological abnormalities. The dorsal fin on two adult males have completely collapsed and folded flat against the body (Matkin et al., 1994). The social structure of the AB pod has also been effected (Raloff, 1993). One matrilineal group from AB pod had broken off and now travels with the AJ pod (Matkin and Saulitis, 1997). With the current ages of the pod members and the sex structure, recovery of the AB pod to prespill levels could take 10 to 15 years (Dahlheim and Matkin, 1994).

Sea otters, Enhydra lutris, were significantly impacted by the Exxon Valdez oil spill. As with any marine mammal, exact numbers were hard to come by. All numbers given, therefore, are estimates. As will be shown later, statistics varied based on who was doing the study.

Sea otters were probably the most studied mammal of this particular spill for two reasons: they were abundant in Prince William Sound, and they were easier to investigate than larger marine mammals (Estes, 1998). The worldwide population of sea otters is approximately 100,000. 13,000 of these reside in Prince William Sound. They may live up to twenty-five years in captivity; their average lifespan in the wild ranges form 10-12 years. One pup per year is produced, and it is nursed for up to six months. Food includes clams, mussels, crabs, and sea urchins (Bodkin and Ballachey, 1997).

The oil spill showed immediate effects on the sea otters. An estimated 2,800 animals perished (Brewer, 1996). A total of 1,000 carcasses were actually recovered, but some studies indicate that this may represent only 20% of total mortalities (Bodkin and Ballachey, 1997). Most otters die of hypothermia following an oil spill. They use their fur as insulation by trapping air. When the coat is covered in oil, the otter cannot successfully protect itself from the cold (Roberts, 1989). Another cause of death may be oil poisoning. This includes: breathing in of hydrocarbon fumes, ingestion of petroleum, and absorption of chemicals through the skin (Raloff, 1993). Lung and liver damage is also evident. In 1989, there was a 35% decline of otters in oiled areas, and a 13% increase of otters in unoiled areas (Ballachey et al., 1994). Thus, some of the sea otters from oiled areas may have migrated to unoiled areas.

Following the spill, rehabilitation efforts were put into effect. 357 sea otters were collected. Of these, 197 were released. 80% of seriously oiled otters died. Not much was known at the time about how otters respond to oil spills. Scientists now conclude, however, that the seriously oiled otters should probably have been euthanized (Raloff, 1993). Some researchers think that those otters that were saved may actually have recovered on their own (Brody et al., 1996). A decision must be made in the future about whether or not these efforts are actually important to the overall population (Jessup, 1998). There was a high mortality rate in released otters as well as a low reproductive rate (Ballachey et al., 1994). The average cost of rehabilitation was an astounding $50,420 per otter (Raloff, 1993).

The Exxon Valdez oil spill carried long-term effects for the sea otters. In 1989-1992, many prime-age animals were found dead (Ballachey et al., 1994). Normally, otter carcasses represent either very young or very old animals. However, in the years after the spill, many animals of reproductive age were found. Studies also indicate that juvenile survival was low. In 1990, there was a 19% decline in oiled areas. Thus, the total since the spill was 54%. There was also a 28% decline in unoiled areas. Some researchers believe this decline in unoiled areas may have been due to the release of disease carrying rehabilitated otters into the unoiled areas (Raloff, 1993). A study of rehabilitated otters that ended up in zoos showed that half of these otters’ pups were stillborn. Also, even when these animals died years later, necropsies revealed significant lung and liver damage (Phillips, 1999).

Determination of past effects and present standings depends on who is doing the calculating:

Both sides should probably be taken with a grain of salt, and the real answers most likely lie somewhere in the middle.

Prince William Sound appears recovered on the surface (Fonda, 1999). However, oil still lingers underneath. From the various marine mammal species, it can be seen that the Exxon Valdez oil spill did significant damage to populations. However, ten years later, most species have either recovered or are stable. Some species have only returned to declines similar to pre-spill times. The oil spill seems to, however, no longer be adding to the damage. All that is needed now is more time.

Ballachey, B.E., J.L. Bodkin, and A.R. DeGange. 1994. An overview of sea otter studies. in Marine Mammals and the Exxon Valdez. Academic Press: 47-59.

Bodkin, J.L, and B.E. Ballachey. 1997. Sea Otter. Restoration Notebook. http://www.oilspill.state.ak.us

Brewer, G. 1996. Marine mammals and the Exxon Valdez. Bioscience. 46: 154-155.

Brody, A.J., K. Ralls, and D.B. Siniff. 1996. Potential impact of oil spills on California sea otters: implications of the Exxon Valdez spill in Alaska. Marine Mammal Science. 12: 38-53.

Calkins, D.G., D.C. McAllister, and K.W. Pitcher. 1999. Stellar sea lion status and trend in Southeast Alaska: 1979-1997. Marine Mammal Science. 15(2): 462-477.

Estes, J.A. 1998. Concerns about rehabilitation of oiled wildlife. Conservation Biology. 12: 1156-1157.

Exxon Valdez Oil Spill Trustee Council. 1999. http://www.oilspill.state.ak.us

Fonda, D. 1999. After the spill: ten years later, Alaska’s wilderness still struggles to heal. Life. 22:103-104.

Frost, K.J. 1997. Harbor Seal. Restoration Notebook. http://www.oilspill.state.ak.us

Frost, K.J., L.F. Lowry, and J.M. Ver Hoef. 1999. Monitoring the trend of harbor seals in Price William Sound, Alaska, after the Exxon Valdez oil spill. Marine Mammal Science. 15(2): 494-506.

Gorbics, C. 1993. The fate of sea otters following the spill. Alaska’s Wildlife. 25(1): 16-17.

Jessup, D.A. 1998. Rehabilitation of oiled wildlife. Conservation Biology. 12: 1153-1155.

Johnson, C.B., and D.L. Garshelis. 1993. Sea otters following the Exxon Valdez oil spill. in Ten Posters Depicting the Results of Scientific Studies of PrinceWilliam Sound and the Gulf of Alaska Following the Exxon Valdez Oil Spill.: 8-9.

McAlpine, Ken. Is the Prince William Sound on the rebound? Aqua. March 1999: 84-89.

Phillips, N. 1999. Oil spill scarred otters. Anchorage Daily News. http://www.and.com/evos/stories/199032/50.html

Piper, Ernest. The Exxon Valdez Oil Spill: Final Report, State of Alaskan Response. Alaska Department of Environmental Conservation. June 1993: 50-82.

Raloff, J. 1993. An otter tragedy: understanding the sea otter’s vulnerability to oilhas proved costly to all involved. Science News. 143: 200-202.

--- 1993. A (killer) whale of a mystery. Science News. 143: 126.

Roberts, L. 1989. Long, slow recover predicted for Alaska. Science. 244:22-24.

Wiliams, T.M., and R.W. Davis. 1991. Sea otters thrive in Prince William Sound, Alaska. Pamphlet: 1-4.

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