By: Alexandra Smith

Sea otters can simultaneously hold a fuzzy pup on their chest, and an entire ecosystem on their back. Usually found munching on a sea urchin snack or grooming their thick coat of fur, these charismatic creatures are quite possibly the most influential organisms in their rapidly changing ecosystems. These marine mammals are found along the coasts of California, Oregon, Washington, Canada, Alaska, and even Japan and Russia (1). Sea otters (Enhydra lutris) were hunted to near extinction in the 1700’s and 1800’s by fur traders but are fortunately now protected by the 1911 International Fur Seal Treaty, as well as the U.S.’ Marine Mammal Protection and Endangered Species Acts of the 1970’s. Thanks to policy and reintroduction efforts in California, Washington, and British Columbia, otter populations are holding steady, but are still much lower than historical numbers (2).

Sea Otter Range. Image: Copyright 2019 Davis, Bodkin, Coletti, Monson, Larson, Carswell and Nichol. — Sea Otter Range. Image: Copyright 2019 Davis, Bodkin, Coletti, Monson, Larson, Carswell and Nichol.

Sea otters are a keystone species - meaning that they play such an essential role in their environment, that if they were removed, the ecosystem would drastically change for the worse. Organisms such as kelp and urchins are dependent on sea otters. This iconic trio allows for a brilliant, balanced, well-functioning ecosystem. Sea otters’ favorite meal is urchin, and urchins love to eat kelp. So where there are urchins, there are sea otters that eat them. And where there are sea otters, there are flourishing kelp forests. At least, there should be.

Currently, kelp forests are in trouble. As sea otter populations decline, predation pressure on sea urchins does too. In a healthy ecosystem, urchins will remain in cracks and crevices and wait for drifting kelp to come to them. But as urchin populations skyrocket in the wake of dwindling sea otter presence, they begin to emerge from the cracks and actively hunt (3). They’re ravenous - ravaging entire kelp forests rapidly and perilously. The once thriving underwater forests of kelp are reduced to barren wastelands at the hands of an echinoderm army. What’s worse is that kelp forests are only the first to go. In an urchin desert, local declines in fish, bird, and seal populations are inevitable. This is the current situation that began in the 1990’s - in Alaska’s Aleutian Island chain, the sea otter population decreased due to an uptick in killer whale attacks (4). Without otters, the kelp forests were depleted, and the wide variety of organisms that relied on kelp for shelter, food, and habitat became threatened. Kelp forests are also excellent at absorbing carbon dioxide from the atmosphere (which is currently in excess due to the burning of fossil fuels) and protecting coastlines from storm surge and erosion (5).

*Urchin Barren Landscape, Channel Islands National Park. Photo: National Park Service*

Sea otter populations are not only decreasing in Alaska, but virtually everywhere. They are currently considered “endangered” by the IUCN Red List. Whether indirectly or directly, humans are sea otters’ biggest threat. The risk of an oil spill is one of the leading dangers they face. These spills are tragic for all marine life, but especially for sea otters, who lack blubber and rely on their fur (the densest of any mammal!) to keep warm. The oil seeps into their fur and makes it lose its insulative property, and worse yet, gets ingested by the otter.

Due to climate change causing more frequent severe weather events like El Niño, otters are at risk of losing their pups and not having a reliable food source. Other threats include illegal hunting, general pollution, car/boat strikes, fishing gear entanglement, and even flushable kitty litter that introduces a harmful parasite found in cat feces to the otters (5).

A recent 2019 study found a new threat to recovering sea otter populations: they are being attacked by white sharks along the California coast. White sharks normally go for elephant seals and other large, blubbery marine mammals. Though recently, they have been biting sea otters in an “exploratory” way, much like sharks bite humans (6). Once the sharks realize they have a mouthful of fur and no blubber, they move on. However, these bites are often fatal to the otter.

Conserving sea otter populations is imperative. As a keystone species, their presence is essential for maintaining health and stability in their unique ecosystem. Protecting sea otters is synonymous to protecting every other organism in their environment.

The Marine Mammal Protection Act asserts that efforts to recover sea otter populations must be made, such as “creating and implementing a plan for returning them to healthy population levels” (7). Native peoples in Alaska are allowed to harvest sea otters as it is part of their culture, and they help the U.S. Fish and Wildlife Service conduct population surveys and engage in important conservation dialogue. In California, there is a Sea Otter Fund that taxpayers may contribute to. Since 2007 it has raised over $3 million to fund important research and conservation initiatives (5).

Not everyone is on board to save the sea otters. Shell fishermen worry that the reintroduction of sea otters may cause their industry to take a hit, however the benefits certainly outweigh the costs. A recent study from the University of British Columbia used a trophic model to estimate the economic ecosystem benefits of reintroduced otters. The results suggest that the presence of sea otters yields 37% more total biomass annually, therefore increasing the value of: finfish, carbon sequestration, and ecotourism by over $40 million USD (8). This will, in turn, exceed the annual loss to invertebrate species by over $5.5 million USD.

A healthy underwater environment, namely kelp forests, which support invertebrates, fish, birds, and countless other organisms, is not possible without the sea otter.

Sources:

(1) “Sea Otter Natural History.” SeaOtters.com, www.seaotters.com/sea-otter-natural-history/

(2) “Sea Otter.” Defenders of Wildlife, defenders.org/wildlife/sea-otter.

(3) Bland, Alastair. “As Oceans Warm, the World's Kelp Forests Begin to Disappear.” Yale E360, 20 Nov. 2017, e360.yale.edu/features/as-oceans-warm-the-worlds-giant-kelp-forests-begin-to-disappear.

(4) Estes, J. A., et al. “Killer Whale Predation on Sea Otters Linking Oceanic and Nearshore Ecosystems.” Science, American Association for the Advancement of Science, 16 Oct. 1998, science.sciencemag.org/content/282/5388/473.abstract.

(5) “Sea Otter Conservation.” SeaOtters.com, www.seaotters.com/sea-otter-conservation/.

(6) Moxley, Jerry H., et al. “Non‐Trophic Impacts from White Sharks Complicate Population Recovery for Sea Otters.” Wiley Online Library, John Wiley & Sons, Ltd, 30 Apr. 2019, onlinelibrary.wiley.com/doi/10.1002/ece3.5209.

(7) Doroff, Angela, and Alexander Burdin. “The IUCN Red List of Threatened Species.” IUCN Red List of Threatened Species, 5 Jan. 2013, www.iucnredlist.org/species/7750/21939518.

(8) Gregr, Edward J., et al. “Cascading Social-Ecological Costs and Benefits Triggered by a Recovering Keystone Predator.” Science, American Association for the Advancement of Science, 12 June 2020, science.sciencemag.org/content/368/6496/1243.

How A Threatened Keystone Species Holds Its Ecosystem In Place