Recovery Strategy for the Sea Otter ( Enhydra lutris ) in Canada December 2007
Sea Otter Recovery Team. 2007. Recovery Strategy for the Sea Otter (Enhydra lutris) in Canada.Species at Risk Act Recovery Strategy Series. Fisheries and Oceans Canada, Vancouver. vii+ 56pp.
Accessed February 20 2014 at http://www.dfo-mpo.gc.ca/Library/336961.pdf.
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1.5.2 Description of threats
Oil contamination has both immediate and long-term effects on sea otters and the recovery of their populations. The following five points summarize sea otter vulnerability to oil contamination.
•Sea otters depend upon the integrity of their fur for insulation. Oil destroys the water-repellent nature of the fur. As it penetrates the pelage, it eliminates the air layer and reduces insulation by 70% (Williamset al.1988). This usually results in hypothermia.
•Once the fur is fouled, sea otters ingest oil as they groom themselves. Ingested oil damages internal organs, which in turn has chronic and acute effects on sea otter health and survival.
•Sea otters are nearshore animals with strong site fidelity, and will remain in or return to oiledareas, additionally, they often rest in kelp beds, which collect and retain oil.
•Sea otters are found in single sex aggregations, which can include 100 or more animals. Thus, large numbers of sea otters, representing a substantial portion of the reproductive potential of a population, can become simultaneously fouled by oil. The loss of a raft of male otters may have less reproductive impact than the loss of a raft of female otters because of the species’ polygynous mating system.
•Sea otters feed on benthic invertebrates, which can accumulate and store toxic hydrocarbons during, and after, an oil spill. The status of the sea otter population in Prince William Sound illustrates both short-term and long-term impacts of oil contamination. In the spring of 1989, the oil tanker Exxon Valdez ran aground in Prince William Sound, spilling 42 million litres of crude oil. Nearly 1000 sea otter carcasses were recovered within six months, but total mortal ity estimates ranged from 2,650 (Garrott et al. 1993) to 3,905 (DeGange et al. 1994). Presently, sea otters in parts of the Sound that were most heavily oiled continue to have significantly higher levels of cytochrome P4501A, a biomarker for hydrocarbons, than otters in less heavily oiled areas. This suggests continued exposure to residual oil in prey and habitat. P opulation growth is significantly lower in the heavily oiled area, as well, and it is thought that recovery is constrained by residual oil effects, despite an adequate food supply, and by emigration (Bodkin et al. 2002). Population modelling using data from 1976 to 1998 shows that sea otters in Prince William Sound had decreased survival rates in all age-classes in the nine years following the spill. The effects of the spill on survival appear to have dissipated mostly as those animals alive at the time of the spill have died
(Monson et al. 2000b), but the Prince William Sound sea otter population has not yet fully recovered to pre-spill levels. The risk of oil spills in BC has been of consider able concern for sometime, particularly since the Nestucca oil spill, December 22, 1988 (Waldichuk 1989), and the Exxon Valdez spill that occurred less than six mont hs later (Loughlin 1994). The Nestucca spill released 875,000 litres of Bunker C oil off Grays Harbour, Washington. The current, combined with onshore winds, carried the oil slick northward f ouling the shoreline of western Wa shington and the west coast of Vancouver Island. Weathered oil reached as far as the Goose Islands Group on the central coast of BC (Watson 1989). Sea otter surveys made so on after the spill found one oiled sea otter carcass on an offshore islet in Checleset Bay and wolf scats containing oiled sea otter fur on Vancouver Island in the affected area. While ther e is little doubt sea otters did die from oil contamination, the exact number could not be established because wolves and bears quickly scavenge beach-cast carcasses. Boat-based surveys made the following summer found no detectable effect on the population (Watson 1989), although variation among sea otter counts can be quite high, making trends often difficult to ascertain. Although the impact of the spill appears to have been minimal, the event, nonetheless, demonstrated the vulnerability of the sea otter population to oil contamination. Sources of oil spill thre ats in the marine waters around BC include cargoes of tankers and barges, bilges, fuel tanks of marine vessels, shore-based fuelling stations and even shore-based industries such as pulp mills (Shaffer et al.1990). In the early 1990s, more than 7000 transits were made annually by freighters and tankers in Pacific Canadian waters, including at least 1500 tanker trips to or from Alaska, and more than 350 loaded tankers entered the Strait of Juan de Fuca (Burger 1992). The greatest volume of petroleum and risk comes from shipments of crude oil and refined petroleum products. Based on data from 1988 a nd 1989, over 26 million cubic metres of crude oil were transported annually in to and out of the Strait of Juan de Fuca, mostly carried by
tankers, and an additional 15 million cubic metres of refined petroleum products, carried mostly by barges (Shaffer et al.
1990). About 15% of these loads were delivered to coastal depots along the west coast of Vancouver Island (Shaffer et al.
1990). It is unlikely that the volume of petroleum transported has declined since the late 1980s, in fact it is more likely to have increased with the growing human population (Schaffer et al. 1990). Risk models developed at that time predicted the follo wing oil spill frequencies for the marine waters of southern BC and northern Washington:
•spills of crude oil or bunker fuel exceeding 159,000 litres (100barrels) could be expected every 2.5 years;
•spills of any type of petroleum product exceeding 159,000 litres (1000 barrels) could be expected every 1.3 years (Cohe n and Aylesworth 1990). The actual frequency of large spills affecting BC between 1974 and 1991 was fairly close to the predicted frequency (see table in Burger 1992). In addition to spills of at least 159,000 litres, there are numerous smaller spills. Spills over 1,113 litres (7 barrels) are considered significant by Environment Canada and are tracked. Along the west coast of Vancouver Island, there are at
least 15 reportable spills of more than 1,113 litres (7 barrels) annually (Burger 1992). A recent development proposal to deliver crude oil by tank er from Kitimat, BC, to Asia Pacific and California markets (Enbridge Inc.2005) and proposals to allow drilling for oil and gas in Hecate Strait and Queen Charlotte Basin (BC Ministry of Energy Mines and Petroleum Resources) pose additional risks and could alter the above predictions about the size and frequency of spill events. Environmental Contaminants – Persistent Bioaccumulating Toxins Organochlorine contaminant levels have not been measured in Canadian sea otters.
Polychlorinated biphenyls (PCB), organochlorine pesticides including DDT and butyltin have been measured in sea otters from California, Washington and Alaska (Bacon et al. 1999; Kannan et al. 2004; Lance et al. 2004). PCBs concentrations were higher in Alaskan otters from the Aleutian Islands (309μg/kg wet weight) compared to otters from California (185μg/kg wet weight) and southeast Alaska (8μg/kg wet weight) (Bacon et al. 1999). Total DDT concentrations were highest in California sea otters (850μg/kg wet weight), compared to the Aleutian Islands (40 μg/kg wet weight) and southeast Alas ka (1μg/kg wet weight), likely reflecting the greater degree of agricultural activity in California than in Alaska. The levels of PCBs measured in California and Aleutian sea otters is considered to be of concern, since similar levels cause reproductive failure in mink, a closely related species (Risebrough 1984 in Riedman and Estes 1990). Although the leve ls of DDT measured in California sea otters were not considered to be exceptionally high when compared to other marine mammals (Bacon et al. 1999), reduced immune competence is a well-documen ted side-effect of contaminants in marine mammals and is considered a possible factor in th e high rate of disease-caused mortality in the southern sea otter population (Thomas and Cole 1996; Reeves 2002; Ross 2002). Among a small sample of beach-cast carcasses re trieved for contaminant analysis in California, those that died from infectious disease contained, on average, higher concentrationsof butyltin compounds (components in antifouling paint) and DDTs than animals that had died from trauma and unknown causes (Kannan et al. 1998; Nakata et al.1998).ted (Riedman and Estes 1990) and the population decline reversed. Increased mortality in fishing gear is again under consideration, along with disease, as a cause of the current decline in southern sea otters (USFWS 2003). Incidental entanglements in fishing gear ha ve been reported in Alaska (USFWS 1994) and Washington. There have been accidental takes in the Makah tribal set-net fishery for salmon (Gearin et al. 1996; Gerber and VanBlaricom 1998). The extent of accidental drowning of sea otters in fishing gear in coastal BC is unknown, but not thought to be significant at this time based on the current range of sea otters. However, as the sea otter population expands into areas of gill-net fisheries, there may be local effects and entanglement may emerge as a threat of concern in the future (Watson et al. 1997). Sea otters die from drowning in various crab and fish trap fisheries in California and Alaska (reviewed in Lance et al. 2004). Crab traps may present a threat to sea otters, particularly since they are set in shallow waters within the species’ diving depth range.
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