Chapter VII — Marine Mammal Management in Alaska 



the Kenai Peninsula, 198 animals from the Kodiak 

 Archipelago, and 135 that died at rehabilitation 

 centers or aquaria. Prior to the spill, the number of 

 otters in Prince William Sound was estimated to be as 

 high as 10,000 animals; the number of otters in the 

 Gulf of Alaska was estimated to be at least 20,000 

 animals. Post-spill population estimates are not yet 

 available. 



The cause of death for many otters was hypother- 

 mia. This was due to matting of fiir by oil, which 

 caused the loss of its insulating capability. Others 

 died from acute toxic effects. Necropsies on otters 

 that died at rehabilitation centers during the first three 

 months after the spill revealed high rates of lung 

 lesions, particularly pulmonary emphysema. Toxic 

 hydrocarbon fractions evaporate rapidly in the first 

 hours and days after a spill, and the observed lung 

 abnormalities probably were caused by inhaling toxic 

 vapors in the early stages of the spill. All but two of 

 the severe cases of emphysema were found in the first 

 six weeks after the grounding. High rates of liver 

 abnormalities and high concentrations of hydrocarbons 

 in the blood also were reported from otters that died 

 at the rehabilitation centers. Stress from capture and 

 handling also may have contributed to the death of 

 some animals. 



Efforts to mitigate the effects of the spill by 

 rehabilitating oiled otters resulted in 329 animals 

 being captured live and brought to rehabilitation 

 centers for cleaning. Before the centers closed in 

 September 1989, 193 otters were either reintroduced 

 back into the wild or placed in aquaria because they 

 were judged unsuitable for release. Of the animals 

 released into the wild, 45 of the healthiest animals 

 were fitted with radio transmitters to help assess 

 subsequent survival rates. In March 1991, it was 

 reported that 16 of the tagged animals were still alive, 

 13 were known dead, 15 were missing, and the 

 transmitter on one animal was known to have failed. 



There are indications that sea otters continue to be 

 exposed to and be affected by petroleum hydrocar- 

 bons. Blood and fat samples collected in 1990 from 

 otters in previously heavily oiled areas had elevated 

 concentrations of certain aromatic compounds. 

 Elevated petroleum hydrocarbon concentrations also 

 continued to be found in sea otter prey items taken 



from oiled areas. In addition, mortality rates among 

 prime aged otters (ages 2 to 8 years) in heavily oiled 

 areas were abnormally high in 1990, and preliminary 

 data from the spring of 1991 suggest yearling mortal- 

 ity is higher in oiled areas than in non-oiled areas of 

 the sound. 



Harbor seals also were affected by the spill. Live 

 oiled seals were unusually lethargic and unwary. The 

 carcasses of 19 seals were recovered and some 200 

 harbor seals were estimated to have been killed. Most 

 of the dead animals were not recovered because seals 

 usually sink when they die. The only estimate of 

 harbor seal numbers in Prince William Sound was in 

 the mid-1970s when the population was estimated to 

 be 3,000 to 5,000 animals. Surveys of selected 

 haulout areas in 1984 and 1988 indicate that harbor 

 seal numbers were declining in the sound before the 

 spill for reasons that are not known. After the spill, 

 between 1988 and 1990, they continued to decline at 

 a similar rate at non-oiled sites (13 percent mortality) 

 but at a significantly greater rate at oiled sites (35 per- 

 cent mortality). 



Harbor seals may have encountered and ingested 

 oil or oil-contaminated prey for some time after the 

 spill. Petroleum hydrocarbons found in bile samples 

 taken from seals sampled a year after the spill were 

 five to six times higher in previously oiled than in 

 non-oiled areas. It also is possible that the elevated 

 levels were caused by metabolizing fat reserves 

 deposited during the spill. 



Effects on killer whales are uncertain. Based on 

 extensive pre-spill information, nine distinct pods of 

 killer whales, including approximately 182 animals, 

 occurred in the sound before the spill. Through 

 photo-identification techniques, it was determined that 

 one pod known to contain 36 animals six months 

 before the spill had seven fewer animals one week 

 after the spill. The missing animals remained unac- 

 counted for in 1990 and six more animals disappeared 

 from the pod. Such losses are highly unusual and 

 may be related to the spill. However, it is also 

 possible that factors other than the spill are respon- 

 sible. 



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