Piatt and Naslund 



Chapter 28 



Abundance, Distribution, and Population Status in Alaska 



proportion of total salmon catch observed, it appears that 923 

 and 714 Brachyramphus murrelets (84 percent Marbled) were 

 killed in Prince William Sound gill net fisheries in 1990 and 

 1991, respectively. A more careful analysis of 1990 data, 

 using mean bycatch rates per week and gill net effort, indicates 

 that 1 ,468 (95 percent confidence limits 8 1 3-2043) seabirds 

 (97 percent murrelets) were killed in nets in 1990 (Wynne 

 and others 1991). Of 18 murrelet specimens examined, 16 

 (89 percent) were in adult breeding plumage and 2 were 

 juveniles. Most murrelets were caught in late July just prior 

 to the post-breeding period for murrelets. 



In 1989, there were 1,972 salmon drift net permits and 

 4,947 set net permits issued for the Gulf of Alaska (DeGange, 

 pers. comm.; DeGange and others 1993). Extrapolating 

 from Prince William Sound with 598 drift net permits, and 

 assuming that 1000 murrelets die there in nets annually, 

 then as many as 900, 1 100, and 300 murrelets may drown 

 in gill nets in Southeast Alaska, lower Cook Inlet, and 

 along the Alaska Peninsula, respectively. In total, some 

 3300 (2940 adult) murrelets may drown in fish nets annually 

 throughout their range in Alaska. Assuming a population 

 size of 280,000 individuals, of which 70 percent are adult 

 breeders, then as much as 1.5 percent of adult mortality 

 may derive from drowning in nets. This estimate does not 

 include mortality in set nets, pound nets or seine nets, 

 which anecdotal evidence suggests also kill a number of 

 murrelets each year. 



Oil Pollution 



Chronic low-volume oil pollution is a significant source 

 of seabird mortality in many parts of the world (Burger and 

 Fry 1993, Piatt and others 1991), but effects on murrelets in 

 Alaska are largely unknown, owing to the remoteness of 

 bird populations in Alaska and the sparse human population. 

 Two oil spills in 1970 may have each killed about 100,000 

 seabirds, mostly murres (McKnight and Knoder 1979). 

 Limited beach survey data suggests that low-level mortality 

 occurs throughout the year. In 1988 and 1989 alone, 43 oil 

 spills involving 14 million gallons of oil were reported in 

 Alaskan waters (including 1 1 million from the Exxon Valdez). 

 Several of these spills were in the vicinity of major seabird 

 colonies, but damages were not documented. Chronic oil 

 pollution is likely to get worse as fishing fleets expand and 

 more oil, and gas development occurs in offshore 

 environments (Lensink 1984). 



Following the Exxon Valdez oil spill in Prince William 

 Sound during March 1989, about 30,000 seabirds were 

 recovered and the actual kill toll ranged between 100,000- 

 300,000 birds (Piatt and others 1990). Both Marbled and 

 Kittlitz's murrelets were affected by the spill, as were many 

 other alcids. A total of 6 1 2 Marbled Murrelets were retrieved 

 from beaches. Another 413 unidentified murrelets were 

 recovered and, if we prorate these birds by the proportion 

 that were Marbled Murrelets in each area of recovery, then 

 the total number of Marbled Murrelets retrieved was 808. 

 Only a fraction of birds killed at sea made it to shore (ca. 10 



percent), and if we apply recovery rates estimated by 

 Ecological Consulting, Inc. (1991) and Piatt and others (1990) 

 for each region affected, then about 8400 Marbled Murrelets 

 were killed by the Exxon Valdez oil spill (see also Kuletz 

 1994). This represents a one-time loss of 3 percent of the 

 total Alaska population, and about 7 percent of the population 

 in the spill zone (Kuletz 1994). Similarly, about 530 Kittlitz's 

 Murrelets were killed, or about 3 percent of their total Alaska 

 population (van Vliet 1993). 



Boat Traffic 



Owing to their coastal distribution and use of relatively 

 sheltered marine habitats, murrelets are more exposed to 

 vessel activities than most other seabirds in Alaska. 

 Disturbance can disrupt feeding birds and persistent boat 

 traffic may prevent murrelets from using important foraging 

 areas (Speckman, pers. comm.). Even in areas where murrelets 

 may habituate to existing boat traffic, changes in boat activity 

 may influence murrelet foraging activity. Following the Exxon 

 Valdez oil spill in Alaska, boat activity increased greatly in 

 Prince William Sound and Kachemak Bay because of rescue 

 and clean-up efforts. There, Kuletz ( 1 994) found that murrelet 

 numbers were negatively correlated with numbers of boats 

 and low-flying aircraft. Evidence also suggested that breeding 

 may have been disrupted (Kuletz 1994). Increasing activity 

 by fishing, commercial, tourist and private boats in areas 

 known to be important for murrelets (e.g., Glacier Bay 

 National Park, Prince William Sound, Kenai Fiords National 

 Park, and Kachemak Bay) may have important long-term 

 implications for murrelet populations in Alaska. The potential 

 impact of vessel disturbance on murrelet foraging and breeding 

 success requires more study. 



Other Factors Influencing Population 

 Dynamics 



Natural Changes in the Environment 



A variety of independent data indicate that a marked 

 "change of state" in the marine ecosystem of the Gulf of 

 Alaska occurred during the last 20 years (Piatt and Anderson, 

 in press). This shift has been manifested by marked changes 

 in sea water temperatures, composition of marine fish 

 communities, reduced overall fish biomass, and dramatic 

 changes in the diet and population ecology of higher 

 vertebrates that depend on those fish populations (Piatt and 

 Anderson, in press). In particular, productivity and populations 

 of Common Murres (Uria aalge), Black-legged Kittiwakes 

 (Rissa tridactyla), Stellar sea lions (Eumetopias jubatus), 

 and harbor seals (Phoca vitulina) declined dramatically in 

 , various areas of the Gulf of Alaska during the 1980's. Declines 

 in Marbled Murrelet populations in Alaska (see below) also 

 coincided with these changes in the marine ecosystem, and 

 may be related to changes in forage fish availability during 

 this time. Between the late 1970's to the late 1980's, high 

 quality capelin (Mallotus villosus) were replaced largely by 

 lower quality pollock (Theragra chalcogramma) in the diets 



292 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



