MARINE MAMMAL COMMISSION — Annual Report for 1991 



cies and organizations, the Council adopted a Federal- 

 State Natural Resources Damage Assessment Plan in 

 April 1989 for the first year of assessment work (i.e., 

 through 28 February 1990). 



As discussed in previous Annual Reports, the 1989 

 assessment plan included 58 studies. Seven projects 

 costing approximately $1,900,000 addressed marine 

 mammal work. Nearly half of those funds was 

 devoted to work on sea otters; the remainder was 

 allocated to studies of effects on humpback whales, 

 killer whales, stranded cetaceans, Steller sea lions, 

 and harbor seals. In 1990, the Council approved a 

 plan for damage assessment work during the second 

 year (1 March 1990 through 28 February 1991). 

 Follow-up work for each of the 1989 marine mammal 

 studies was included, with the exception of work on 

 stranded cetaceans. Funding for the second year of 

 marine mammal studies again totaled about 

 $1,900,000, nearly two-thirds of which was allocated 

 to sea otter studies. 



In 1991, the Council adopted a plan for the third 

 year (1 March 1991 to 29 February 1992) of damage 

 assessment and restoration work. It included studies 

 on sea otters, killer whales, and harbor seals costing 

 approximately $400,000. Studies conducted during 

 the first two years after the spill on humpback whales 

 and Steller sea lions were not continued in 1991. 



Regarding sea otters, the 1991 plan described a 

 three-year project (March 1991 to March 1993) to 

 assess and monitor changes in sea otter densities in 

 Prince William Sound and to describe habitat use 

 patterns. Work scheduled for 1991 included efforts to 

 evaluate, design, and implement aerial and vessel 

 surveys to monitor pup and non-pup densities in 

 different parts of the sound and to compare habitat use 

 patterns in oiled and non-oiled areas. The continua- 

 tion of work in 1992 and 1993 will depend on the 

 results of work in 1991. The cost of work proposed 

 for 1991 was estimated at $176,600. Work also will 

 continue on monitoring otters instrumented with 

 transmitters and released back to the wild prior to 

 1991. 



The goal of harbor seal studies was to gather data 

 on the abundance, behavior, and habitat use patterns 

 of seals in previously oiled and non-oiled areas of 



Prince William Sound. A pilot study was planned to 

 attach satellite transmitters to five seals (two in April 

 1991 and three in September 1991), to evaluate the 

 ability of the devices to gather data on seal move- 

 ments, diving patterns, feeding locations, and haulout 

 patterns. Also planned was an aerial survey of the 

 sound during the autumn molt to continue monitoring 

 the trend in seal numbers in oiled and non-oiled areas. 

 The estimated cost of harbor seal work for the 1991 

 planning period was $181,500. 



The focus of work on killer whales was on improv- 

 ing the basis for identifying and describing habitat 

 requirements. Planned work included continuing 

 photographic identification to document the composi- 

 tion of killer whale pods resident in Prince William 

 Sound; gathering and synthesizing all published and 

 unpublished killer whale sighting data relative to the 

 spill area; correlating that data with data on water 

 depth, sea surface temperatures, and the catch of 

 killer whale prey species in commercial fisheries; and 

 developing an assessment of habitat use patterns in 

 Prince William Sound. Also planned was an assess- 

 ment of the feasibility of developing and applying 

 satellite transmitters to tracking killer whales in 1993. 

 The estimated cost of the killer whale work during the 

 1991 planning period was $43,500. 



Summary of Oil Spill Impact 



Because of legal considerations related to pending 

 lawsuits against Exxon seeking reimbursement for 

 spill damages, results of damage assessment studies 

 were not released in 1989 or 1990. Given a pending 

 settlement of the Governments' suits early in 1991, 

 however, a summary of impacts was made available 

 in March 1991. The settlement later fell apart and 

 further details were withheld. Available assessments 

 of the nature and magnitude of effects therefore 

 remain preliminary. The following describes effects 

 of the spill on marine mammals based on preliminary 

 information released as of the end of 1991. 



The most apparent oil spill impact on marine 

 mammals was to sea otters. Preliminary estimates of 

 the number of otters killed directly by the spill range 

 fi-om 3,500 to 5,500 animals. During 1989, 1,011 

 sea otter carcasses were recovered from the spill area, 

 including 490 from Prince William Sound, 188 firora 



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