18 USGS/BRD/ITR-2000-0012 



most important in mid-shelf and coast habitats, 

 respectively. During the breeding season (May-August), 

 rockfish predominated in outer-shelf habitats. Pacific 

 whiting and euphausiids were most important in 

 mid-shelf habitats, and northern anchovy and rockfish 

 in coast habitats. In winter (September-February), 

 rockfish, squid, and euphausiids were important in 

 outer-shelf habitats, whereas squid and anchovy 

 predominated in mid-shelf and coast habitats, 

 respectively. Throughout the year, northern anchovy 

 were important in coast habitats, and rockfish were 

 important in outer-shelf and coast habitats. Diet also 

 varied by feeding location, even within a season, which 

 suggested that if primary prey species became 

 unavailable, murres switch feeding locations or change 

 their diet dramatically. Rockfish and northern anchovy 

 also are the primary prey fed to murre chicks at the 

 South Farallon Islands (Ainleyetal. 1990, 1993). Farther 

 away from colonies in central California, rockfish, 

 market squid, northern anchovy, night smelt (Spirinchus 

 starksi), and ling cod (Ophiodon elongatus) were 

 important prey in gill-net killed murres in Monterey 

 Bay in spring, summer, and fall, but varied seasonally 

 and between years (Croll 1990). Euphausiids were not 

 important prey in spring and squid dominated during 

 summer 1 983. Fish also were the principal prey in winter 

 in Monterey Bay, although some squid were taken (Baltz 

 and Morejohn 1977). 



In British Columbia, murres have been reported 

 feeding on Pacific sand lance, Pacific herring, northern 

 anchovy. Pacific whiting, smelts (Osmeridae), other 

 small fish, marine crustaceans, and small squids (Munro 

 and Clemens 1931; Guiguet 1972; H. R. Carter and 

 S. G. Sealy, unpublished data). Murres are well known 

 to use estuarine waters to exploit abundant Pacific 

 herring during spring spawning (e.g., Straits of Georgia) 

 or in juvenile-herring rearing areas in late summer and 

 fall (e.g., Barkley Sound; Munro and Clemens 1931; 

 Robertson 1972; Vermeer et al. 1987; Campbell et al. 

 1990; H. R. Carter and S. G. Sealy, unpublished data). In 

 gill-net killed murres in late summer and early fall 1 993- 

 96 in the San Juan Islands, Washington, murres fed 

 primarily on Pacific herring, Pacific sand lance, 

 salmonid smolts (Oncorhynchus sp.), and Pacific tomcod 

 (Wilson and Thompson 1998). 



At-sea Distributions 



California 



Extensive at-sea surveys were conducted monthly 

 from 1975 to 1978 in southern California and from 1980 

 to 1982 in central and northern California (Briggs et al. 

 1981, 1983, 1987; Tyler et al. 1993). Common murres 



were present at high densities in shelf-slope habitats 

 near colonies in central and northern California 

 throughout the year. During the breeding season, 

 densities averaged 6-12 birds per km 2 but peaked at 

 20-200 birds per km 2 near colonies. Highest average 

 densities (12-18 birds per km 2 ) were recorded in late 

 July to September, after departure of chicks and adults 

 from colonies. Two major factors affect the use of these 

 foraging areas: the distribution of suitable breeding 

 habitats and the distribution and abundance of prey. In 

 California, colonies are present in productive coastal 

 areas with localized upwelling often located downstream 

 from coastal promontories. These conditions probably 

 result in abundant prey resources near colonies most of 

 the year, allowing for year-round residency in these 

 areas. Between January and July, small numbers of 

 murres are found between colony areas in northern and 

 central California (i.e., southern Humboldt to southern 

 Sonoma Counties). Densities can increase in this area 

 in winter (Briggs et al. 1983), apparently because of 

 wider foraging by murres from northern California and 

 possibly southern Oregon. In winter, lower densities of 

 murres are present in offshore habitats in central and 

 northern California and shelf-slope habitats in southern 

 California that experience cool, locally upwelled waters. 

 Very small numbers of murres winter in warmer waters 

 in the southern part of the Southern California Bight 

 and northern Baja California, Mexico (Unitt 1984; 

 Howell and Webb 1995). 



During the breeding season in central California, 

 virtually all murres were observed in waters 200 m or 

 less in depth and adjacent to shore (less than 35 km 

 from colonies; Briggs et al. 1988; Ainley et al. 1990). A 

 large feeding area located 8-25 km northeast of the 

 Farallon Islands was used regularly from mid-April to 

 early June. In early spring, murres fed in deep waters at 

 the shelf edge near the Farallon Islands. However, murres 

 also are widely present in nearshore waters in the Gulf 

 of the Farallones during the breeding season, as far south 

 as northern San Luis Obispo County and as far north as 

 southern Sonoma County (Bolander and Parmeter 1 978; 

 Roberson 1985). As the season progressed, murres began 

 to shift toward the shallower coastal waters along the 

 nearby mainland coast. After fledging, adult-chick 

 groups dispersed along the coast, both south (e.g., 

 Monterey Bay) and north (e.g., Bodega Bay). Late 

 summer movement of murres into Monterey Bay for 

 at-sea chick rearing and prebasic molt are followed with 

 movement out of the bay into offshore waters in fall 

 (Croll 1990). 



During El Nino conditions, murres feed closer to 

 shore during summer and some traditional feeding areas 



