44 USGS/BRD/ITR-2000-0012 



Resistance-Double complex) may have been nearly 

 extirpated during this decline since only 23 birds were 

 found in 1987. However, this colony grew to 380 birds 

 by 1990, possibly because of intercolony movements 

 from nearby colonies within this complex. However, a 

 remarkable increase occurred at the South Farallon 

 Islands between 1989 and 1990. In retrospect, this 

 upswing signaled the end of the decline and the start of 

 an increase for the central California population. Ground 

 and boat surveys and plot counts from 1 989 to 1 995 at 

 the South Farallon Islands also confirmed the end of 

 decline by 1990 (Sydeman et al. 1997, 1998). 



The decline of the central California population 

 between 1979 and 1989 and the loss of the Devil's Slide 

 Rock and Mainland colony have been attributed mainly 

 to extensive gill-net and oil-spill deaths, and reduced 

 productivity related to the severe 1982-83 El Nino 

 (Carter 1986; Carter and Ainley 1987; Salzman 1989; 

 Takekawa et al. 1990; Wild 1990; Piatt et al. 1991; 

 Swartzman and Carter 1991; Carter et al. 1992, 1995; 

 Ainley et al. 1994; Sydeman et al. 1997; McChesney et 

 al. 1998, 1999). More than 75,000 murres died in 1979- 

 87 in central California as a result of gill-net fisheries 

 (Takekawa et al. 1990). High mortality was attributed 

 to the consistent spatial and temporal overlap of large 

 numbers of feeding murres and high gill-net fishing 

 effort in nearshore waters of Monterey Bay, Gulf of the 

 Farallones, and Bodega Bay area from 1980-86. Most 

 severe declines occurred at colonies located nearest areas 

 of highest gill-net mortality. Two major oil spills occurred 

 during this period and killed more than 8,000 murres. 

 In November 1984, the Puerto Rican oil spill occurred 

 off the Golden Gate, killing 1,500-2,000 murres (PRBO 

 1985; Fordet al. 1987). Mortality probably was focused 

 on large colonies at the Farallon Islands and Point Reyes. 

 In January-February 1 986, the Apex Houston oil spill 

 occurred between San Francisco and Monterey Bay, 

 killing 6,300-7,500 murres (Page and Carter 1986; Ford 

 etal. 1987; Page etal. 1990; Siskin etal. 1993). Mortality 

 probably was spread more widely over all colonies with 

 greatest impacts at Devil's Slide Rock and Mainland, 

 Castle Rocks and Mainland, and Hurricane Point Rocks. 

 The loss of the Devil's Slide Rock and Mainland colony 

 (first noted in June 1986) was associated with this 

 mortality, although earlier gill-net mortality had reduced 

 the colony beforehand (Takekawa et al. 1990; Piatt et 

 al. 1991; Swartzman and Carter 1991). Many smaller 

 spills also killed thousands of murres between the late 

 1970s and 1989 (Stanzel et al. 1988; Carter 1997; Nur 

 etal. 1997). 



Low productivity in the 1982-83 El Nino 

 undoubtedly affected the ability of the central California 

 population to recover in the late 1980s. However, it was 



not possible to detect whether or not increased deaths 

 of adult or subadult murres resulted during severe El 

 Nino-induced winter weather conditions in 1982-83. 

 At this time, high numbers of murres killed in gill nets 

 were washing up on beaches but the cause of death for 

 many nonoiled beached birds could not be determined 

 (Stenzel et al. 1988). A small part of the reported decline 

 at certain colonies may have been related to (1) 

 methodological differences between surveys in 1979- 

 82 and 1985-89, (2) undocumented human disturbances 

 from low overflights and boats, or (3) depredation at 

 colonies by peregrine falcons (Falco peregrinus) and 

 common ravens (Corvus corax', Sydeman 1993; 

 McChesney et al. 1998, 1999; M. W. Parker, 

 unpublished data). 



The marked decline in the central California murre 

 population between 1979 and 1989 far outweighed the 

 relatively small increase by 1995 after this decline. 

 Between 1985 and 1995, the total population increased 

 5.9% per annum (P = 0.002), whereas colony complexes 

 increased between 4.6 and 7.2% per annum 

 (0.001 <P< 0.020), excluding the extirpated Devil's 

 Slide complex (Figures 2.3 and 2.4; Appendixes C, D, 

 and H). In 1992, severe El Nino breeding conditions 

 occurred and murre attendance at the South Farallon 

 Islands was low (Sydeman et al. 1997). However, 

 whole-colony counts at the South Farallon Islands and 

 Points Resistance-Double complexes were still higher 

 in 1993 than in 1987-89. The North Farallon, Point 

 Reyes, and Points Resistance-Double complexes 

 increased after 1990. At the Castle-Hurricane complex, 

 increase was not noted between 1987 and 1993, but 

 higher numbers did occur in 1 994-95. Overall, increases 

 that began at the South Farallon Islands in 1990, and 

 later at most other colonies, were sustained despite 

 interruption by the severe 1992-93 El Nino. Highest 

 colony complex counts in the 1993-95 period were 

 still lower than peak counts in the 1979-95 period 

 (Figure 2.3; Appendixes C and D). Increases in 1993- 

 95 at the largest complexes (i.e., South Farallon Islands, 

 North Farallon Islands, Point Reyes, and Points 

 Resistance-Double) are encouraging, but natural 

 recovery of the central California population to 1979- 

 82 levels may require at least another decade without 

 additional major detrimental effects. Human disturbance 

 at colonies has been reduced greatly through additional 

 regulations and enforcement. However, sporadic 

 disturbance events continue. For example, extensive 

 disturbance to breeding murres resulted from low 

 overflights by a U.S. Coast Guard helicopter responding 

 to the grounding of the M/V Wayfarer at Point Reyes in 

 1995 (McChesney etal. 1 998; Thayer etal. 1998, 1999). 



