It is estimated that the worldwide population of sea otters once numbered between several hundred thousand to over one million before being nearly hunted to extinction by fur traders in the 1700s and 1800s. Sea otters finally gained protections with the signing of the International Fur Seal Treaty of 1911, and became listed under the Marine Mammal Protection and Endangered Species Acts in the 1970s (6). Worldwide, numbers have slowly recovered but still stand far below original population numbers. While sea otters are vulnerable to natural predators, their populations are significantly impacted by several human factors as well.
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Conflict With Humans
Direct conflict with humans, such as shootings and entrapment in fishing traps and nets pose a major threat to sea otter populations. Since sea otters eat many of the same shellfish humans like to eat, such as sea urchins, lobster and crab, they often find themselves in the same areas fishermen like to harvest (6). Some shell fishers view sea otters as competition and a threat to their economic gain. Fishing gear that can cause entanglement and drowning, including nets, traps, and fishing debris, is a conservation concern for many marine species; with respect to Sea Otters, this threat is difficult to quantify as drowned Sea Otters sink and are largely undetected. Whether intentionally or unintentionally, sea otters who find themselves too close to a fisherman’s harvest are often harmed or killed. Fortunately, the number of sea otters deaths from human conflict is slowly decreasing as a result of their protection under the The Endangered Species Act and increased regulation of fishing nets. The Endangered Species Act (ESA) is the strongest and most important federal law protecting imperilled wildlife and plants for nearly 40 years and has helped prevent the extinction of our nation's wildlife treasures (6) |
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Oil Spills
Oil spills from offshore drilling or shipping are an immense threat to sea otter populations. When sea otters come into contact with oil, it causes their fur to mat, which prevents it from insulating their bodies. Without this natural protection from the frigid water, sea otters can quickly die from hypothermia. The toxicity of oil can also be harmful to sea otters, causing liver and kidney failure as well as severe damage to their lungs and eyes. Sea Otters often rest in kelp beds, which can collect and retain oil. A historic example of the impacts oil spills have on sea otters is the 1989 Exxon Valdez oil spill in Alaska’s Prince William Sound, which killed approximately 2,800-3,800 sea otters. Sea otters are still threatened by events like this because countries around the northern hemisphere continue to ship and drill for oil throughout the Pacific and along coastal areas that sea otters call home. Because their numbers are low and they are located in a rather small geographic area compared to other sea otter populations. |
Vessel Trafic
The British Columbia coast is an active waterway with heavy vessel traffic (Figure 3) and oil spills are an ever-present threat in British Columbia waters as acute or chronic spills may occur from the cargoes of tankers and barges, bilges, fuel tanks of marine vessels, shore-based fuelling stations and even shore-based industries (3). Since then the demand for oil has increased to over five billion litres through the Port of Vancouver in 2013 and further substantial increases are proposed (6). Oil spill risk is greatest in winter months and major vessel routes that transit close to shore present the highest environmental risk to sensitive nearshore ecosystems. Sea Otters are vulnerable to sea vessels travelling around the British Columbia coast due to both Canadian and American industries. This increases the risks for all marine life around the coast to ecosystem destruction or vessel accidents. The sea otter range encompasses the entire length of a major shipping route that experiences heavy oil tanker and container ship traffic along the Pacific Coast (6). Overall, the threat of collisions with vessels is considered to be a “low” level of concern for the Sea Otter population because most of the population occurs in relatively remote coastal regions with low levels of vessel traffic. Sea Otters occupy exposed rocky shorelines that are often not suited to high speed transit close to shore. For the Sea Otter this threat can be characterized as collisions with high speed small boats operating in nearshore waters. There have been a few incidents in British Columbia in which carcasses have been recovered with evidence of boat propeller marks or blunt force trauma associated with impact from a boat (6). |
Figure 4: Vessel Traffic Density for all ships in 2013, as reported by Marine Communications and Traffic Services
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Habitat Degradation
Pollution from land runs off into the ocean which contaminates the sea otters’ habitat. This can jeopardize their food sources, as well as harm them directly. Sea otters are often contaminated with toxic pollutants and disease-causing parasites as a result of runoff in coastal waters (6). In British Columbia, parasites and infectious disease cause more than 40% of sea otter deaths and hundreds of sea otters have succumbed to the parasites Toxoplasma gondii and Sacrocystis neurona, which are typically bred in wild small mammals such as opossums (3). Scientists have also reported the accumulation of man-made chemicals, such as PCBs and PBDEs, at some of the highest levels ever seen in marine mammals (6). |
Illegal kill
Overall, the threat of illegal kill is considered to be a “medium” level of concern because it has the potential to significantly impact the population by uncontrolled removals of animals, especially reproductive aged females (6). The current level of illegal kills is unknown and the paucity of information makes it difficult to estimate the total number of illegal kills. There are verified reports of illegal killing of Sea Otters in British Columbia and for terrestrial game species it is conservatively estimated that only 10% of illegal kills are accounted for (6). In southeast Alaska, the Sea Otter population growth rate slowed to 4.7% per year from 1988 to 2003, despite ample amounts of unoccupied habitat still available for expansion (3). The slowing growth rate does not appear to be attributable to disease, predation or limiting resources and may be related to illegal and legal harvest. |
https://alaskafurid.wordpress.com/2009/11/02/otter-sea/
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