Sea Otter Conservation
California’s southern sea otter has been listed as a threatened species under the Endangered Species Act since 1977. 41 years later and counting, their conservation status remains unchanged and their future uncertain. Sea otter population growth has stalled in recent years and many hurdles for full population recovery remain. There are only about 3,000 southern sea otters left in the wild today.
Why Are Sea Otters Important?
Sea otters are an iconic species, representing the beauty and diversity of marine life found along California’s coastline. They’re also considered a keystone species because of their critical importance to the health and stability of the nearshore marine ecosystem. They eat sea urchins and other invertebrates that graze on giant kelp. Without sea otters, these grazing animals can destroy kelp forests and consequently the wide diversity of animals that depend upon kelp habitat for survival. Additionally, kelp forests protect coastlines from storm surge and absorb vast amounts of harmful carbon dioxide from the atmosphere. Sea otters are also considered a sentinel species because their health reflects that of California’s coastal waters.
Why Aren’t They Recovering?
Recent studies have shown that fatal white shark bites have increasingly become the leading cause of sea otter mortality in California, a concerning trend that is likely impacting range expansion and population recovery. Scientists also attribute a substantial percentage of southern sea otter mortality to infectious diseases, many of which are known to have anthropogenic causes and land-to-sea linkages. White shark bites, pathogens and parasites, food availability, nutritional deficiencies, habitat degradation, coastal pollutants and contaminant exposure are among many of the contributing factors threatening the recovery of the species. And the risk of a major oil spill remains a serious threat.
What’s Being Done About It?
Researchers are working hard to gain a better understanding of what’s threatening sea otters so we can find ways to help them recover. Determining precisely how all of the factors driving elevated mortality are impacting the overall health of the southern sea otter population and the nearshore marine ecosystem on which they and other species depend is critical. The goal is development and implementation of effective, long-term management and mitigation strategies that can lead to the recovery and delisting of the species.
Threats and Issues
The single greatest cause of southern sea otter mortality by far is fatal white shark bites. Shark-bitten sea otters now account for more than half of all stranded sea otters recovered in California, exceeding all other causes of sea otter mortality combined. The increase in shark bite mortality now appears to be impacting population growth and expansion at the peripheries of the range, areas of the population that typically fuel the colonization of new habitats. Sea otter range expansion to the north and south will be critical for full recovery of the population but unfortunately these are the very areas where increased shark bite mortality has been greatest.
- California sea otter numbers take a slight dip from last year, but average count exceeds 3,090 for third consecutive year
- Increasing White Shark Bites Now Leading Cause of Sea Otter Mortality in California
- Monterey Bay Aquarium Study: Gaps in kelp cover may threaten the recovery of California sea otters
Disease and Contaminants
California’s sea otters acquire many infectious diseases because of elevated pathogen and contaminant pollution levels in nearshore waters. Part of sea otters’ high susceptibility to exposure is due to their diet. With incredibly high energy requirements, sea otters must consume approximately 25% of their bodyweight in prey each day just to stay alive. A large proportion of this prey consists of filter-feeders, such as mussels and clams. These organisms indiscriminately sieve particles out of the water and can accumulate high concentrations of pollutants and disease pathogens. When otters repeatedly forage on these contaminated prey, over time they can expose themselves to harmful or even lethal doses.
Sea otter harassment and other wildlife disturbance represents more than 40 percent of all violations recorded annually in Monterey Bay National Marine Sanctuary. The harmful consequences harassment can potentially have on sea otter adult females, especially those caring for pups, is particularly concerning. The demanding maternal costs associated with pup rearing for adult female sea otters make them exceptionally vulnerable to energetic deficits — this includes the additional energy expenditure caused by harassment by humans. If a resting otter is harassed and forced to dive, the animal must expend additional energy to swim away only to begin grooming all over again, which takes away precious time it would otherwise have to rest or care for its young undisturbed. Research has revealed that females with 6 month old pups spend up to 14 hours a day foraging, while consuming nearly twice as much food as females with no pups. Their daily energetic demands are challenging enough, but superimpose harassment on top of an already strenuous energy budget and it may be ultimately too much for the animals to overcome, making them more vulnerable to infection and disease, and increase the likelihood they abandon their pups as they aren’t able to provide for them.