Bio227-6: The Otter Side of Cute and Cuddly

The Southern Sea Otter

Sophia Liu

Scientific name: Enhydra lutris nereis

Type of listing: Threatened

Originally approved: February 3, 1982

Listing date: February 24, 2003

Description and Ecology of the Southern Sea Otter

The sea otter is the smallest species of marine mammal in North America, with adult males reaching 135 cm and females reaching 125 cm. Compared to their northern counterparts, southern sea otters are slightly smaller and lighter. They have evolved to only inhabit a small geographic zone, tending to stay near the shore where there are both rocky surroundings and kelp beds. Sea otters are considered a keystone species. This means that they are vital in maintaining balance in their ecosystem. Their feeding habits help to maintain kelp forests from being devoured. Physiological features include padded forepaws, hind limbs for paddling, and a coat of guard fur and underfur. Sea otters are unique in that there is no reserve fat or blubber for storing energy of insulating; otters stay warm entirely through the air their fur traps.

For the most part, sea otters consume invertebrates, with the exception of certain areas of otters that consume fish. It has been concluded that when population density increased, both dietary variation and time allotted to feeding increased as well.

Geographic and Population Changes

The history of the sea otters has seen many highs and lows. Following a period of overexploitation that almost led to extinction, sea otters were first legally protected in 1911 through the passing of the Fur Seal Treaty. Recovering colonies then saw a strong decline in areas in western Alaska, which was hypothesized to be caused by killer whale predation. Thus, the world population of sea otters that was previously estimated to be in the 100,000’s during the late 1900’s is realistically probably much lower. Between the northern and southern subspecies of sea otters, it is apparent that the latter has expanded consistently south along the coast. Wide-range surveys beginning in 1982 have given much insight into the population trends of sea otters. As shown in the graph, there has been a subtle decline in population since the mid-1990’s, but overall, the number of sea otters has been relatively stable. Currently, the southern sea otter population stands at 2,150 individuals along the central and southern coast of California.

Historical range of sea otters

Current range of southern sea otter

Cause of Listing and Main Threats to its Continued Existence

Number of sea otters counter during spring surveys (1983-2001)

In 1977, the southern sea otter was listed because of two primary reasons: small population size and distribution and threats by oil spills to the remaining habitat and population. Traditionally, a large oil spill has posed the largest threat to sea otters. This is due to the fact that a spot of oil on an otter’s coat renders its fur unable to provide insulation, rendering the otter defenseless against the frigid waters. However, the lack of oil spills alongs the California coast along with a stagnant population leads researchers to believe that there are various other potential threats to be considered. These threats could involve habitat pollution, accidental take from fisheries, newly-introduced diseases, and adjacent habitats. The fact that the coast of California, the main habitat for the southern sea otter, is continually growing as an industrial and manufacturing area of importance means that the risk of a large oil spill or more deadly encounters with companies is growing.

Description of Recovery Plan

In accordance with the Endangered Species Act, the recovery plan’s goal is to establish ideal conditions to ensure the long-term survival of the otters, ultimately delisting them. To do so, the team will have to identify the reason why the population is not increasing, continue to reduce the threat of oil spills, and minimize harm that comes from accidental encounters with commercial fishing. A very specific goal of 3,090 individuals over a span of 3 years is set. However, because the otter population is currently stagnant, it is hard to put on a timeline when the projected delisting might occur. It is worth noting that the goal of 3,000 or so otters is considered unsustainable, so although they may be delisted, they are still considered at risk. A brief overview of the many threats posed against otters lends insight into how much must really be done to ensure the well-being of these creatures. Some of these threats listed include “restriction of range due to management zone, disease, incidental take in fishing gear, oil spills, contaminants,” etc. (Recovery Plan)