Chapter 28 



Abundance, Distribution, and Population Status of 

 Marbled Murrelets in Alaska 



John F. Piatt 1 



Nancy L. Naslund 2 



Abstract: Ship-based surveys conducted throughout Alaska dur- 

 ing the 1970's and 1980's, and more recent small boat surveys 

 conducted in the northern Gulf of Alaska, suggest that about 

 280.000 murrelets reside in Alaska during summer. Most Marbled 

 Murrelets are concentrated offshore of large tracts of coastal conif- 

 erous forests in southeast Alaska, Prince William Sound, and the 

 Kodiak Archipelago. About 1- 3 percent of murrelets breed wholly 

 outside of forested areas in Alaska, and these presumably all nest 

 on the ground. At sea, murrelets tend to occupy sheltered waters of 

 bays, fiords, and island straits, and often aggregate near large river 

 outflows or tide rips. Small boat surveys of Prince William Sound 

 and Christmas Bird Count trends suggest that Marbled Murrelet 

 populations in Alaska declined by about 50 percent between 1972 

 and 1992. Population declines may have resulted from cumulative 

 effects of oil pollution, gill netting, logging of old-growth breed- 

 ing habitat, and natural changes in the marine environment. The 

 Exxon Valdez oil spill killed an estimated 8,400 murrelets in 1989, 

 or about 3 percent of the Alaska population. The toll from chronic 

 pollution is unknown. About 3300 murrelets (89 percent adult) die 

 annually in fishing nets in Alaska a sustained adult mortality 

 rate of 1 .5 percent per annum. The extent or effect on murrelets of 

 logging in Alaska are unknown. While only 7 percent of the 

 old-growth has been harvested in the Tongass National Forest, 

 about 40 percent of the highly productive old-growth in the forest 

 has already been logged. A decline in forage fish populations in 

 the Gulf of Alaska during the last 20 years may account for 

 reduced breeding success and population size of several seabird 

 species, including murrelets. Murrelet populations should be sen- 

 sitive to small increases in adult mortality from the above factors 

 because production by murrelets is low and must therefore be 

 balanced by a low annual adult mortality rate. 



The North American subspecies of the Marbled Murrelet 

 (Brachyramphus marmoratus marmoratus) breeds primarily 

 in old-growth coniferous rainforests along the west coast 

 from California to Alaska. Populations of this subspecies 

 range as far west as the Aleutian Islands and north into the 

 Bering Sea. The Asian subspecies B. m. perdix occurs from 

 the Commander Islands and west throughout the Sea of Okhotsk 

 (Ewins and others 1993). However, this subspecies is 

 sufficiently distinct morphologically and genetically from the 

 North American subspecies to be considered a separate species 

 (the "Long-billed Murrelet"; Friesen and others 1994a; Piatt 

 and others 1994). Thus, Alaska contains the extreme western 

 and northern range of the Marbled Murrelet in North America. 



'Research Biologist. Alaska Science Center, National Biological Ser- 

 vice. U.S. Department of Interior 1011 East Tudor Road. Anchorage, AK 

 99503 



Wildlife Biologist. Migratory Bird Management, U.S. Fish and Wild- 

 life Service, U.S. Department of the Interior, 1011 East Tudor Road, 

 Anchorage. AK 99503 



The bulk of the North American population of Marbled Murrelet 

 resides in Alaska. Population estimates have ranged from 

 hundreds of thousands to millions (Ewins and others 1993), 

 but recent estimates suggest that about 250,000 murrelets 

 reside in Alaska (Mendenhall 1992; Piatt and Ford 1993). In 

 this chapter we review information on the abundance and 

 distribution of Marbled Murrelets in Alaska, and the status of 

 populations. Except for the congeneric Kittlitz's Murrelet (B. 

 brevirostris), all other auks breed in colonies and nest on the 

 ground mostly on predator-free islands. In Alaska, a small 

 proportion of Marbled Murrelets also breed on the ground, 

 usually on rocky or sparsely vegetated inland slopes (Day 

 and others 1983; Marks, pers. comm.; Mendenhall 1992). 



Abundance and Distribution 



Survey Methods 



Whereas most surface-nesting seabirds may be censused 

 conveniently at their colonies, population f r imates of burrow- 

 nesting, nocturnal, and forest-nesting eabirds are more 

 difficult to obtain. Murrelet population estimates are based 

 solely on counts of birds at sea (Carter and Ericksen 1992; 

 Klosiewski and Laing 1994; Mendenhall 1992; Nelson and 

 others 1992; Piatt and Ford 1993; Rodway and others 1992, 

 in press; Sealy and Carter 1984; Speich and others 1992). A 

 wide variety of observation platforms and sampling methods 

 have been used to collect data and extrapolate abundance 

 which makes it difficult to pool or compare data from adjacent 

 geographic areas. 



No method for censusing murrelets at sea has ever been 

 ground-truthed for accuracy. Studies of at-sea behavior of 

 murrelets in British Columbia (Carter and Sealy 1 990; Rodway 

 and others, in press; Sealy and Carter 1984), southeast Alaska 

 (Speckman and others 1993), and Oregon (Varoujean and 

 Williams, this volume; Strong and others, this volume) reveal 

 that time of day and season, tide state, and weather conditions 

 are all important variables influencing murrelet aggregation 

 behavior, distribution, and detectability. High temporal 

 variability in murrelet abundance at sea undermines the 

 confidence we may have in the accuracy of absolute population 

 estimates although statistically precise (15-30 percent) 

 measures of abundance are available in some areas (e.g., 

 Barkley Sound, Carter and Sealy 1990, Sealy and Carter 

 1984; Prince William Sound, Klosiewski and Laing 1994). 



Surveys conducted at smaller spatial or temporal scales 

 than those over which movements of birds occur may 

 underestimate populations (Rodway and others, in press). 

 The detectability of murrelets declines with distance from 

 the observer and rough sea conditions (Kuletz 1994), and 



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



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