Of all the species to impact the sea otter, humans have likely done the most harm due to the species. For a variety of reasons in the past and present, humans have damaged the sea otter population. From hunting to oil spills to entanglement in fishing gear, there are a variety of ways in which the humans harm the sea otter population.
Hunting
Firstly, commercial hunting is the most prevalent way in which the sea otter population was harmed by humans (Environment Canada, 2011). During the 17th and 18th centuries, the sea otter was hunted for its valuable pelt. Hunting was not regulated, and consequently the population quickly diminished. Although though the global community eventually took notice and banned the commercial hunting of sea otters in 1911 (Environment Canada, 2011), it was too late. About 20 years later, the last known sea otter in Canada was shot and killed. If it was not for this horrific exploitation of the sea otters, there would have been no need for a reintroduction plan, and the population size would be stable, and likely at carrying capacity.
Oil Spills
Now that the otter population is relatively small and vulnerable, oil spills have become of major concern to sea otter populations. The reason the otter is so greatly affected by oil spills is because of predisposed traits. Firstly, oil will destroy the water repellent nature of their fur, which will reduce insulation by up to 70%. Once the fur is fouled, the otter will groom itself continuously, causing them to ingest oil and cause internal organ damage (Environment Canada, 2011). As a result, the most prevalent cause of sea otter death in an oil spill is hypothermia. There are methods for cleaning the water and rehabilitating sea otters caught in oil spills, however the methods are costly and depend on finding the otters before they freeze (Environment Canada, 2011).
Another reason that sea otters are susceptible to oil spills is because they often travel in large same-sex rafts (Environment Canada, 2011). If one raft of 200 males were to be caught in an oil spill, this would greatly reduce the fertility of the sea otter population moving forward, and likely have significant population trauma many years into the future (Environment Canada, 2011). However this issue is not expected to stop, because it is predicted that major oil spills off the western coast on North America will occur every 1.3 years. Annually, it is expected that there will be at least 15 oil spills of the coast of Vancouver alone (Province of British Columbia, 2003). This issue presents a challenging problem for scientists who know that despite the danger, oil transportation must continue along the North American west coast.
Fishing Gear
Mortality due to entanglement in fishing gear and collisions with vessels is also high in sea otter populations. Specifically, incidental drowning in sunken gill nets was a significant cause of death in the late 1970’s (Environment Canada, 2011). To combat this problem, restrictions were introduced fishermen, which prevented the use of gill nets inside a water depth of 65 meters (which is outside the normal sea otter habitat) (Environment Canada, 2011). However, there are still frequent accidents involving sea otters drowning in fishing nets up and down the west coast. As the population continues to expand, this will be an ongoing issue which will need to be quickly dealt with to ensure the safety of the otter population.
Other Issues
Other issues such as environmental contaminants have affected the otter population in the past, such as the use of DDT, however these issues are not currently prevalent. It is encouraging to note however, that since illegal hunting has all but stopped, and the government is calculating exactly how to reduce human induced sea otter death. They have calculated that it is acceptable for there to be around 140 sea otter deaths each year due to human interactions (Environment Canada, 2011). Although this may sound high, it takes into account oil spills, and this prediction is a tool in devising plans to further limit human induced otter death.