Pink-footed shearwater (Puffinus creatopus) COSEWIC assessment and status report: chapter 8
Limiting Factors and Threats
With regard to Canada specifically, there have been recent discussions concerning the lifting of the current moratorium on gas and oil exploration off the coast of British Columbia. Areas that might be affected by drilling include Queen Charlotte Sound, shallow areas within Hecate Strait and off the north coast of Vancouver Island (K. Morgan pers. comm. 2003). These coincide with areas used by Pink-footed Shearwaters. Should drilling and development occur, the potential fouling of Pink-footed Shearwaters as well as detrimental impacts upon their foods, is highly likely.
The main terrestrial threats facing the Pink-footed Shearwater are from introduced predators, human disturbance and exploitation, and habitat destruction (Schlatter 1984). The importance of each of these differs between breeding locations (Guicking and Fiedler 2000).
Coatis (Nasua nasua), introduced to Robinson Crusoe Island during the 1930s (Inter-American Biodiversity Information Network 2003), are believed to have contributed to severe population declines of Pink-footed Shearwaters in the past (Guicking and Fiedler 2000). Although present in somewhat reduced numbers relative to their abundance prior to the 1980s (Hahn and Römer 2002), they are believed to be the greatest threat to the population of Pink-footed Shearwaters at this location (Guicking and Fiedler 2000). Feral cats (Felis catus) and rats (Rattus spp.) are also present (Bourne et al. 1992, Hahn and Römer 2002, Hodum and Wainstein 2002), and almost certainly impact colonies. Historical accounts indicate that cats have been present since the early 1700s (P. Hodum pers. comm. 2003). Hodum and Wainstein (2003), in a preliminary attempt to assess predation threats by rats, cats and coatis on Robinson Crusoe, estimated that, on average, a maximum of 6% of Pink-footed Shearwater nests in three study plots failed as a result of predation, either of the chick or an adult. Rats are also known to occur on Santa Clara, and probable rodent depredation of Pink-footed Shearwaters has also been documented from this island (Hahn and Römer 2002).
Ship (Rattus rattus) and Norway (Rattus norvegicus) rats are known to occur on Isla Mocha, where they have been observed entering burrows. Eggshell fragments have also been found on the forest floor suggesting rat depredation. Feral cats are probably present, in association with the human habitation of the island. Dogs often accompany harvesters into the forest and likely take chicks from short burrows or those sitting outside their burrows (Guicking 1999). Overall, the impacts of rats, cats and dogs on population sizes and trends are unknown (Guicking in litt. 2001, Hodum and Wainstein 2002).
Although the practice of harvesting chicks for food is illegal on Isla Mocha, they are considered a local delicacy and large numbers are harvested each year, from March to May, by the island’s residents. Chick harvesting was first reported in the early 20th century, but the scale of the operation has never been determined. Currently, an estimated 3,000-5,000 chicks are harvested each year (Guicking 1999). The effect of this activity also extends beyond harvesting. While chicks in short, straight burrows can be easily harvested, burrows that are too long or twisted are usually dug open and therefore destroyed. Only those nests underneath massive root systems, or those on steep, inaccessible sites are safe from harvesters (Guicking 1999).
Schlatter (1984) also lists seabird-fishery interactions, pesticide residues, industrial wastes in the waterways, ‘red-tide’ incidents and oil spills as potential risks off the Chilean coast. However, no data exist to quantify their impact on population size or trends (Schlatter 1984). Becker (2000) documented elevated levels of mercury in the feathers of breeding adults from Isla Mocha. In addition and perhaps as expected, the downy plumage of chicks from the same location also contained significant levels of the heavy metal. However, the body feathers of older chicks did not. The author suggests the contamination results from exposure during migration or wintering.
During the breeding season, Pink-footed Shearwaters from Isla Mocha show a strong preference for foraging in areas that also support an extensive fishing industry. Interaction between the species and the fishery is therefore highly likely (Guicking et al. 2001). However, there is currently no information available on the nature or extent of these interactions (Guicking et al. 2001).
Longline commercial fishing tends to be concentrated over the continental shelf of North America (Wahl 1975, J. Smith pers. comm. 2003). As previously mentioned, Pink-footed Shearwaters tend to be associated with the shelf-break in this part of their range (Fig. 3), making the risk of interaction with the fishing fleet highly likely. To date the Department of Fisheries and Oceans have recorded no incidental take of the species in Canadian waters (L. Yamanaka pers. comm. 2003). However, the potential exists for the two to overlap, both spatially and temporally, thus representing the greatest threat to the continued occurrence of the species in Canada. It should also be noted that observer effort within the fishing fleet is low. Between 1999 and 2002, only 1.5-18.5% of the hooks hauled in the halibut longline fishery were observed (Smith and Morgan, in press). Similarly, for the commerical rockfish longline fishery for the same time period, only 0.2-10.5% of the hooks hauled were observed (Smith and Morgan, in press). It is likely that bycatch of Pink-footed Shearwaters has gone unrecorded in the past, and this may continue if observer coverage remains low. As previously mentioned, Pink-footed Shearwaters are also often found with Sooty Shearwaters, a species that incurs severe mortality from fishing gear, especially in the North American Pacific (Guicking et al. 2001). By default the Pink-footed Shearwater may therefore be at high risk as well.
Fouling of Pink-footed Shearwaters by petroleum products also represents a significant potential threat in many parts of the species’ marine range, including the United States and Canada. For Canada specifically, recent discussions concerning the lifting of the current moratorium on gas and oil exploration off the coast of British Columbia highlights this risk. Areas that could be affected by drilling include the shallow waters of Queen Charlotte Sound and Hecate Strait, and off the west and north coasts of Vancouver Island (K. Morgan pers. comm. 2003). On the basis of the Pink-footed Shearwater’s continental shelf distribution, and their tendency to investigate all vessels (see above), the potential therefore exists for fouling through either accidental or deliberate releases of petroleum products from offshore platforms, ships or terrestrial sources. As previously mentioned, oil pollution also has the potential to seriously impact the species’ foraging habitats and/or prey within Canadian waters.
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