Carter and Kuletz 



Chapter 26 



Mortality Doe to Oil Pollution 



an estimate of the total numbers of seabirds killed was 

 constructed, based on numbers of carcasses recovered from 

 beaches and complex extrapolations to account for times 

 and shoreline areas not covered, and the loss of carcasses at 

 sea and on land (Ford and others 1991a); and (2) other 

 NRDA studies were conducted to measure population impacts 

 at breeding colonies and at sea for specific species and areas. 

 All NRDA studies were initiated under the federal 

 Comprehensive Environmental Response, Compensation and 

 Liability Act ( CERCLA) and the Clean Water Act. Population 

 estimates for Marbled Murrelets in Prince William Sound 

 were obtained from NRDA Bird Study No. 2 (Klosiewski 

 and Laing 1994). These population estimates were compared 

 with those derived from similar surveys in 1972-1973 (Dwyer 

 and others 1976) and 1984-1985 (Irons and others 1985). 

 NRDA Bird Study No. 6 examined indices of changes in 

 murrelet numbers and productivity at two locations in the 

 spill zone and collected tissue samples for contaminant studies 

 (Kuletz. in press: Oakley and others 1994). 



Approximately 30,000 seabird carcasses were recovered 

 in the spill zone throughout the spring and summer of 1989 

 through a large-scale effort coordinated by Exxon. Carcasses 

 were processed and identified by U.S. Fish and Wildlife 

 Sen ice personnel. A variety of estimates suggest that at 

 least 240.000 seabirds were killed (Ford and others 199 la; 

 Piatt and Anderson, in press; Piatt and others 1990a). 

 Murrelet carcasses were identified to species (i.e. Marbled, 

 Kittlitz's or Ancient murrelets [B. marmoratus, B. 

 brevirostris. Synthliboramphus antiquus]) whenever 

 possible. However, many carcasses could only be classified 

 as unidentified murrelets. Using U.S. Fish and Wildlife 

 Sen ice data files on identified carcass recoveries, recovery 

 location and estimated carcass recovery rates for each region 

 (Ford and others 199 la), the total mortality estimate was 

 about 8.400 Brachyramphus murrelets (table 1). Most 

 Brachyramphus murrelets were Marbled Murrelets. The 

 estimate included only about 255 Kittlitz's Murrelets. 

 Additional work is required to refine such estimates based 

 on a reexamination of sample carcasses held in freezer vans 



after the spill (Ford and others 199 la). However, based on 

 preliminary analyses, it is unlikely that estimates will change 

 dramatically (Carter, unpubl. data; Ford and others 199 la; 

 Page, pers. comm.). 



The Exxon Valdez spill zone may support roughly half 

 of the estimated 280,000 Marbled Murrelets in Alaska 

 (Mendenhall 1992; Piatt and Ford 1993; Piatt and Naslund, 

 this volume). If so, then approximately 6 percent of the 

 murrelets in the spill zone were killed directly by oil. The 

 carcass recovery rate for murrelets was probably lower than 

 for other seabirds due to their small body size (Ford and 

 others 1991a). Thus, the mortality estimate should be 

 considered a minimum number. 



Despite the high mortality of murrelets, U.S. Fish and 

 Wildlife Service at-sea surveys of murrelet abundance in 

 Prince William Sound were unable to demonstrate an effect 

 of oiling on the marine population, although the total population 

 had declines 67 percent since 1972. Murrelet populations 

 were compared after the spill between oiled and unoiled 

 areas, as well as to 1972 estimates (Klosiewski and Laing 

 1994). Kuletz (in press) suggested that significant oiling 

 impacts were masked in this comparison. First, individual 

 murrelets can forage over wide areas that may be up to 75 km 

 apart (Bums and others 1994), making the assignment of 

 birds to "oiled" or "unoiled" areas an uncertain exercise. 

 Second, murrelets dispersed to widely scattered breeding 

 sites up to a month after the initial oiling event Part of the 

 breeding population in Prince William Sound was exposed to 

 oil prior to entering the Sound. Only about 25 percent of the 

 summer population is present in the Sound in March 

 (Klosiewski and Laing 1994). In nearshore southcentral Alaska, 

 murrelet numbers increase throughout April, and do not reach 

 summer peak numbers until May (Kuletz, unpubl. data; Vequist 

 and Nishimoto 1990). The majority of murrelet carcasses 

 were retrieved in April (Ford and others 199 la, Piatt and 

 others 1990a) and most murrelets may have been killed outside 

 Prince William Sound as they migrated northward and inshore 

 in April. Large numbers are known to winter in the vicinity 

 of Kodiak Island, southwest of the initial spill area in Prince 



Table 1 Estimates of direct mortality of Brachynunphus murrelets from the Exxon Valde oil qntt in Alaska in 1989. Carcasses were identified t 

 Murrelets i. MAMl' I. Kialirz 's Murrelets fKlML'), or unidentified murrelet which includes Ancient Murrelets (see text) 



Marbled 



'Excludes Ancient Murrelets. based on carcasses identified to species (see text). 



USDA Forest Sen-ice Gen. Tech. Rep. PSW-152. 1995. 



263 



