STELLER SEA LIONS: What makes them critical for the health of kelp forests?


Kevin Schafer

What are Steller Sea Lions?

Steller Sea Lions are a type of marine mammal (dolphins, otters, seals, etc.), meaning that they breathe air, have fur, are warm-blooded, and have mammary glands for lactation. More specifically, they are a type of pinniped (seals and sea lions), and even more specifically they are a type of Otariid (sea lions). They are actually the largest Ottariid in the world, with adult males weighing in at as much as 2500 lbs! As of 2014, there are approximately 108,000-123,000 Steller Sea Lions.

Why are they endangered?

The majority of Steller Sea Lion declines occurred between 1977 and 2000, during which the population decreased by 70%. The exact reason for why Steller Sea Lion populations declines is not known, although this is a popular area of research and there are many well-formulated hypotheses on the matter. Many scientists agree that there are three main causes of decline: environmental variability, competition with commercial fisheries, and predation by killer whales


Andy Murch

How is their decline affecting ecosystems? 


Every organism plays a vital role in the balance of an ecosystem. Because of food webs (who eats who), changes in the population size of one animal may have very large impacts on other animals that rely on that animal for food. When this pattern reaches many animals in a food web this phenomena is called a trophic cascade. This is exactly what happened when Steller Sea Lion Populations declined.

Steller Sea Lions were once one of the main food sources of killer whales. However, when sea lion populations began to decline, killer whales were forced to switch to other food sources, such as otters. However, an adult Steller Sea Lion can weigh up to 25x more than an otter, so the killer whales were forced to eat far more otters in order to survive (approximately 1825 otters per year)! This caused decline in sea otter populations of approximately 25% per year throughout to 1990s.

The decline in sea otters is not where this story ends. The trophic cascade continued with the next link in the food web: sea urchins. Sea otters primarily feed on invertebrates (sea urchins, seastars, crabs, etc.), so a decrease in sea otter populations resulted in an increase in the population of invertebrates. Many invertebrates (and in particular, sea urchins) are grazers that forage primarily on marine algae. The increase in sea otters therefore resulted in an increased foraging pressure on local kelp forests, which caused a steep decline the health and size of kelp forests.

sea otter cascade

What is being done to recover populations?

Steller Sea Lions are protected under the Marine Mammal Protection Act of 1972, which makes it illegal to harass, feed, hunt, capture, collect, or kill any marine mammal or part of a marine mammal.

A recovery plan was first published in 1992, and recently revised in 2008. Since the creation of the recovery plant, critical habitat and no-entry zones have been established around Steller Sea Lion rookeries (breeding areas).

There has also been substantial funding dedicated to research the ecology, behavior, genetics, population dynamics, and movements of Stellar Sea Lions. This research is then used to determine reasons for decline and develop more successful management strategies.



Warwick Sloss

What does the future hold?

The western population of Steller Sea Lions currently has a positive growth rate, suggesting that conservation efforts have been beneficial. The other population of Steller Sea Lions (Loughlin’s Steller Sea Lions) have increased by more than 3% per year since the 1970s. Therefore, the Loughlin’s Steller Sea Lions was removed from the ESA threatened species list in 2013, whereas the western population  is still listed as endangered under the ESA.

Although there is always variation in nature, these positive trends and conservation efforts suggest that Steller Sea Lions have a good chance of their populations recovering! 🙂

How can you help?

1. Learn more about Steller Sea Lions!

Killer Whale Predation on Sea Otters Linking Oceanic and Nearshore Ecosystems” by J. A. Estes, M. T. Tinker, T. M. Williams, and D. F. Doak.

2. Volunteer with Steller Sea Lion Research!

Any suggestions? Comment below!

Follow our blog (bottom of page) and Instagram (@beforthesea) for updates on the recovery of endangered species!



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