Restoration of Common Murre Colonies in Central California: Annual Report 2009
This report summarizes the 14th year of restoration and associated monitoring of central California seabird colonies conducted by the Common Murre Restoration Project (CMRP) in 2009. These efforts began in 1996 to restore breeding colonies of seabirds, especially Common Murres (Uria aalge), harmed by the 1986 Apex Houston and 1998 Command oil spills, gill net fishing, human disturbance, and other factors. From 1995 to 2005, our primary goal was to restore the previously extirpated Devil’s Slide Rock colony using social attraction techniques and to assess restoration needs at other central California colonies. Since 2005, efforts have been redirected to surveillance of human disturbance to murre colonies, assessing the impacts of that disturbance, and assessing other factors affecting growth of colonies; additionally, we still monitor progress of the initial restoration efforts. This information is then used to guide outreach and education efforts conducted by the Gulf of the Farallones National Marine Sanctuary and to assess the success of those efforts. The goal of this program is to restore affected breeding colonies mainly through reduction of human disturbance. Surveillance and monitoring were conducted almost daily from mid-April to late July at the following Common Murre colonies in central California: Point Reyes; Devil’s Slide Rock & Mainland; and the Castle-Hurricane Colony Complex. Another four colonies were surveyed weekly including three in the Drakes Bay area (Point Resistance, Millers Point Rocks, and Double Point Rocks) and at San Pedro Rock (near Devil’s Slide). In addition to human disturbance, we measured seasonal attendance patterns, and reproductive performance of Common Murres and up to five other species as well as breeding population sizes for certain species. Periodic surveys were also conducted by volunteers at three colonies near the Golden Gate (Bird Island, Lobos Rock & Land’s End, and Seal Rocks) to follow recent murre colonization attempts. For aircraft, activity rates were measured as the number of fixed-wing planes and helicopters observed per hour that flew < 305 m (1000 ft) above sea level (ASL) over colonies. Boat activity was measured as the number of vessels observed per hour that approached within 457 (1500 ft) of colonies. Aircraft, boat and other anthropogenic disturbance rates were measured as the number of disturbance events per hour. At Point Reyes, combined aircraft and boat activity in 2009 declined 27% from 2008 and overall disturbance rates also declined. In the Drakes Bay area, little aircraft or boat activity was observed at Point Resistance and Miller’s Point Rocks; at Double Point Rocks, combined aircraft and boat activity rates increased from 2008 but disturbance rates decreased for planes and boats. At Devil’s Slide Rock & Mainland, aircraft and boat activity and disturbance rates were the greatest of all colonies that are monitored almost daily. Although combined aircraft and boat activity rates were similar to 2008, plane overflights declined 9% but helicopters and boats increased 19% and 21%, respectively. At the Castle- Hurricane Colony Complex, combined activity rates increased 55% from 2008, including an 83% and 79% increase in plane and boat observation rates, respectively. Although observation rates increased in 2009, the overall disturbance rate decreased 79% from 2008. Unmarked, “other” aircraft (i.e., private or charter) were the most commonly observed planes and helicopters and caused the most observed disturbances (95% of plane, 44% of helicopter overflights). The next most common source of aircraft disturbance was from U.S. Coast Guard planes (n =1) and helicopters (n = 10), including one flushing event. The majority of watercraft observed were recreational small private boats (64%) followed by kayaks (23%). Recreationalsmall private boats and kayaks were responsible for nearly all disturbances (56% and 41%, respectively) and all flushing events (60% and 40%, respectively). On Devil’s Slide Rock in 2009, a new high count of 1,003 Common Murres was established since the colony was occupied in 1996. The number of breeding pairs within monitored plots increased 11% from 2008. However, for the first year since restoration efforts began in 1996, no murre chicks survived to departure from the Devil’s Slide Rock & Mainland colony. Hatching success was extremely low (6.7%), with many eggs being abandoned. Murres bred on the Devil’s Slide Mainland (32 pairs) for the fifth consecutive year but no chicks hatched. Murre breeding success at Point Reyes (0.27 chicks/pair) and Castle Rocks & Mainland (0.35 chicks/pair) was well below the long-term averages. All three Drakes Bay murre colonies suffered total or near total breeding failure. Brandt’s Cormorants had low breeding population sizes and breeding success at all three monitored colonies, concomitant with a large spring starvation event. Numbers of breeding Pelagic Cormorants were similar to or lower than in 2008 at Point Reyes and Devil’s Slide Rock & Mainland but were higher at the Castle-Hurricane Colony Complex; productivity of monitored nests was low. Western Gull numbers were higher than in 2008 but productivity was low. Low breeding success for most seabirds appeared to be caused by low prey availability, especially of small schooling baitfish. At certain colonies, disturbance exacerbated impacts of low prey. In particular, apparently emaciated California sea lions (Zalophus californianus) were observed climbing high up into murre breeding colonies at Point Reyes, Point Resistance and Double Point Rocks; at Point Reyes, sea lions were observed flushing murres off of eggs, contributing to high rates of abandonment by murres. This likely occurred at other colonies as well. Brown Pelicans were responsible for a limited amount of disturbances to murres at Devil’s Slide Rock & Mainland and Castle-Hurricane. At Castle- Hurricane, anecdotal data suggests that pelican disturbance caused some murre egg loss at three subcolonies followed by fairly substantial relaying efforts. Chronic Common Raven disturbance may be contributing to a large decline in the Miller's Point Rocks colony. Frequent disturbance from aircraft and boats may have contributed to total breeding failure at Devil's Slide Rock & Mainland. Additional efforts are needed to reduce aircraft and boat activity at Devil's Slide and to address a recent increase in boat activity at Castle-Hurricane. Special Closures scheduled to occur at some colonies beginning in May 2010 should reduce boat disturbance to seabirds but this will need to be monitored and enforced.