Burger 



Chapter 29 



Marine Distribution, Abundance, Habitats in British Columbia 



Trevor Channel - Cape Beale transect 



CM CO 



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Figure 9 Mean (is.d.) densities of Marbled Murretets on transects of 17.2-19.5 km in Trevor Channel, past 

 Cape Beale and south to Seabird Rocks in June and July of 1979. 1987, 1989, 1991, and 1993 (Burger 1994, 

 Carter 1984). The sample sizes are numbers of transects. Birds seen on the water and flying are shown in 

 shaded and open columns, respectively. 



slight declines in two areas in which many murrelets occurred. 

 The changes were well within the year-to-year variations 

 reported for this coast. Considerable logging of old-growth 

 forests has occurred around Skidegate Inlet and to the north 

 of Juan Perez Sound, but the forests adjacent to Skincuttle 

 Inlet have not been logged. Oil spills and gill-net fisheries 

 do not appear to have been problems for murrelets in any of 

 these areas. The low densities in Massett Inlet shown contrast 

 with records of flocks of 200 or more in the summers of 

 1946 and 1947 (Carter 1984), but large flocks were also 

 present in May 1990 (Rodway and others 1991). There were 

 thus no indications of significant population declines in 

 these parts of the Queen Charlotte Islands, but the data were 

 insufficient to reliably detect any real changes. 



Threats to Marbled Murrelets at Sea in 

 British Columbia 



Oil Pollution 



There is a moratorium on offshore exploration and 

 development of oil fields in British Columbia, and this 

 seems likely to continue. Threats to murrelets come from 

 catastrophic spills from large vessels as well as chronic 

 small- volume spills (Burger 1992. Vermeer and Vermeer 

 1975). The Canadian Coast Guard (1991) reported annual 



transits of 7,000 freighters and tankers off British Columbia, 

 including at least 1,500 tankers. Each year at least 300 

 loaded tankers enter the Strait of Juan de Fuca (Shaffer and 

 others 1990). Overall, the annual shipments of crude oil 

 and refined petroleum products average 26.0 and 15.0 

 million m 3 , respectively, in southern British Columbia and 

 northern Washington (Shaffer and others 1990). Vessel 

 traffic was estimated to increase by 6-1 1 percent between 

 1 989 and 1 99 1 (Canadian Coast Guard 1 99 1 ). A probability 

 model predicted that spills exceeding 1,000 barrels are 

 expected in southern British Columbia and northern 

 Washington every 2.5 years for crude oil, and every 1.3 

 years for all petroleum products (Cohen and Aylesworth 

 1990), and this prediction was close to the actual pattern of 

 spills between 1974 and 1991 (Burger 1992). These studies 

 indicate a high risk from oiling for Marbled Murrelets. This 

 is particularly pertinent in inshore areas off southwestern 

 Vancouver Island in summer and southern Strait of Georgia 

 and Puget Sound in winter, when high murrelet densities 

 coincide with the greatest volumes of tanker traffic and 

 other shipping (Burger 1992). 



The Nestucca spill in December 1 988 killed an estimated 

 143 Marbled Murrelets off Vancouver Island (Burger 1993a), 

 which represents about 0.9 percent of the 1 6,000 birds thought 

 to occur off Vancouver Island (Rodway 1990). Marbled 



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



307 



