COSEWIC Assessment and Update Status Report on the Ancient Murrelet in Canada
- Assessment Summary
- Executive Summary
- COSEWIC History, Mandate, Membership and Definitions
- Lists of Figures and Tables
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- Existing Protection or Other Status
- Technical Summary
- Acknowledgements and Information Sources
- Biographical Summary of Report Writer and Authorities Contacted
Limiting Factors and Threats
The populations of Ancient Murrelets in Canada continue to be under pressure for many reasons. Major factors responsible are outlined below.
The main factor limiting populations in the past century has been the introduction of mammalian predators to island colonies including rats and raccoons in British Columbia. In Canada, rats are considered an important predator of Ancient Murrelets (Drever and Harestad 1998). They have been recorded on 18 islands in the Queen Charlotte Islands (Bertram and Nagorsen 1995) including four with breeding populations of Ancient Murrelets: Kunghit, Lyell, Langara, and Murchison islands (Bertram and Nagorsen 1995). Rats are responsible for declines or extirpation of colonies on Kunghit, Lyell, Langara, Cox, Lucy, Murchison and Bischof islands (Harfenist and Kaiser 1997). For example, in 1992, 50% of occupied burrows on Lyell showed evidence of rat predation (Lemon 1993a) and the 90% decline in the murrelet population on Langara is thought to be the result of rat predation (Bertram 1995). Although rats have now been eradicated on Langara, with none detected since 1996 (Taylor et al. 2000), recolonisation could occur through commercial and pleasure boats (Bertram and Nagorsen 1995).
Another threat to Ancient Murrelets is raccoons. Raccoons have been previously reported from several of the islands with breeding colonies (Helgesen, Limestone, Ramsay, Skincuttle, Saunders and George), but are now found only on Alder islands (Bertram and Nagorsen 1995; Harfenist and Kaiser 1997; Harfenist 2002; Harfenist unpublished data, A. Gaston, pers. comm.; Hipfner 2004, pers.comm.). Raccoons can cause substantial losses to seabird colonies and are likely responsible for declines recorded on Limestone, Saunders and Helgesen islands. For example, in 1991, three adult raccoons on East Limestone Island killed at least 11% of the breeding population of Ancient Murrelets and reduced the number of chicks leaving the colony by 35% (Gaston 1991; Gaston 1992). Following the removal of raccoons during in 1992, the numbers of Ancient Murrelet chicks produced increased by 20%, and adult mortality decreased by nearly 80% (Gaston and Lawrence 1993). Similarly, the population of Ancient Murrelets on Helgesen Island declined by 80% over 7 years when 8-12 raccoons were present (Gaston and Masselink 1997).
Although raccoons have been eradicated from a number of the islands (Helgesen, Little Helgeson, Saunders, E. and W. Limestone) about half of the colonies in the Queen Charlotte Island are vulnerable to invasion (Lemon and Gaston 1999; Hipfner 2004, pers.comm.).
There is some evidence that oceanographic changes could have long-term impacts on Ancient Murrelet populations. A recent comparison between changes in oceanographic conditions and inter-annual changes in breeding biology of Ancient Murrelets in Hecate Strait between 1983 and 1999 showed that long-term changes in ocean conditions could have an impact on the health of the population (Gaston and Smith 2001). Correlations were found between sea-surface temperature and Southern Oscillations as well as mean number of chicks departing per breeding pair and chick departure mass.
The recent decision by the Federal government (initiated by a request from the BC provincial government) to review the moratorium on offshore oil and gas exploration in the Queen Charlotte Basin, specifically in Hecate Strait, is a potential threat to the Ancient Murrelet. If lifted, the exploratory drilling and eventual increase in shipping activity and oil transport (tanker or pipeline) will significantly increase the possibility of catastrophic oil spills in the region. There may also be an increase in nighttime mortalities due to collisions with lines near oil platform lights (Montevecchi et al. 1999). Ancient Murrelets have been heavily impacted by spills in other regions (Harfenist 2003) because oil spills are a particular threat to species that congregate in one area (Harfenist et al. 2002). This might also increase what is a continual threat to these birds--small, low-level spills from ships moving through the region (Harfenist and Kaiser 1997).
By-catch of seabirds continues to be a threat to populations in the Queen Charlotte Islands. Estimates suggest that 25,000 seabirds may be killed annually in fishing gear off the British Columbia coast (Morgan et al. 1999). Ancient Murrelets have been caught in gill nets near Langara Island. Fisheries may have been the cause of the large, early decline in this population in the 1950s and 1960s, and may continue to play a part in the health of Ancient Murrelets on Langara (Bertram 1995). Overfishing of Ancient Murrelet prey species may also have a negative impact on this species (Harfenist et al. 2002).
Disturbance of nesting or feeding birds by tourists or other human activity in the region where Ancient Murrelets are found is a continual concern. Recreational boating and camping can damage habitat or injure chicks or adults (Harfenist et al. 2002). Lights around campsites and on boats are known to disorient birds during nights with low overcast and fog (Harfenist et al. 2002, A. Gaston, pers. comm.).
Forestry activities could directly affect Ancient Murrelet breeding activities by reducing habitat quality, both through removal of the forest canopy preferred by the birds and through compaction of soil, making burrowing difficult. Logging has been suggested as a confounding variable in the lack of recovery at the Langara Island colony (M. Chutter, pers. comm. 2004).
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