Sea lions and sea otters are two charismatic marine mammals that inhabit the coastal waters of the North Pacific Ocean. If you’ve ever wondered if massive California sea lions feast on the small, cute sea otters, you’re not alone.
The quick answer is that while rare, some male sea lions have been known to prey on juvenile sea otters when food is scarce near breeding colonies. However, sea otter predation is not a regular part of sea lions’ diets.
The Diets of Sea Lions and Sea Otters
What Sea Lions Eat
Sea lions are carnivorous marine mammals that belong to the family Otariidae. There are six extant species of sea lions, including the California sea lion, Steller sea lion, Australian sea lion, New Zealand sea lion, South American sea lion, and the Galapagos sea lion.
Sea lions typically feed on fish, squid, octopus, crab, lobster, shrimp, and other seafood. Their diet can vary depending on the species, location, season, and availability of prey. For example, California sea lions off the coast of California primarily eat anchovies, sardines, mackerel, rockfish, and market squid.
In contrast, Australian sea lions mostly consume southern school whiting fish, red cod, small shark species, octopus, and squid. Overall, sea lions are opportunistic predators that adapt their diet based on the productive habitats they occupy.
Some key facts about the diets of different sea lion species:
- California sea lions – Sardines, anchovies, mackerel, whiting, salmon, rockfish, squid
- Steller sea lions – Pollock, cod, salmon, herring, rockfish, cephalopods, crustaceans
- Australian sea lions – Whiting, red cod, octopus, small sharks, lobster, squid
- New Zealand sea lions – Opalfish, red cod, octopus, squid, lamprey, salmon
- South American sea lions – Anchovies, hake, squid, sardines, rock cod
Sea lions are capable of consuming around 4-8% of their body weight in prey each day. A mature 800 pound male California sea lion, for example, might eat 30-60 pounds of fish and squid per day to sustain itself.
Sea lions employ various hunting techniques to catch prey, including stealth ambushes, rapid bursts of speed, and cooperative group hunting strategies. Their diverse diet provides sea lions with sufficient nutrition and energy to maintain their active lifestyles.
What Sea Otters Eat
In contrast to sea lions, sea otters have a highly specialized diet consisting almost exclusively of marine invertebrates like sea urchins, abalone, clams, mussels, crabs, snails, and occasional small fish.
Unlike other marine mammals, sea otters do not have a thick layer of blubber to keep them warm. Instead, they rely on their extremely dense fur coat for insulation. This lack of blubber requires sea otters to consume around 25-30% of their body weight each day to stay warm and survive – making them one of the most voracious marine predators for their size.
Some key facts about sea otter diets and foraging habits:
- Sea otters eat 20-30 different marine species, but prefer sea urchins, abalone, crabs, clams, and snails
- Individual otters specialize in hunting 2 or 3 preferred prey types
- Sea otters eat at the ocean floor or bring food to the surface to eat while floating on their backs
- They use rocks to dislodge prey and crack open shells
- Sea otters consume around 25% of their weight daily, or 15-20 pounds for an average adult
Sea otters are keystone predators in the kelp forest and intertidal ecosystems they inhabit. By feeding on sea urchins, they prevent overgrazing of kelp beds. Their foraging also helps regulate commercially-valuable shellfish populations.
Decades of hunting and habitat loss caused sea otter populations to plummet, but conservation efforts have helped stabilize their numbers in recent years. Maintaining healthy sea otter populations is crucial for balancing nearshore marine food webs.
Documented Interactions Between the Species
Territorial Behavior
Sea lions and sea otters occupy somewhat overlapping habitats along the North American west coast. Both species tend to congregate in areas with plentiful food sources and haul-out sites. This can lead to competition over territory.
Sea lions are much larger and more aggressive than otters. There are documented cases of male sea lions chasing otters out of preferred fishing and resting areas. Sea lions will bark and charge towards the otters, clearly intent on driving them away.
While concerning, these interactions seem to be isolated events centered around prime habitat. Otters appear adept at avoiding confrontation by simply swimming or rafting away from antagonistic sea lions. Still, habitat loss remains an issue if otters are continually displaced from vital areas.
Predation Events
In the wild, most documented cases of sea lions preying on otters involve young pups. The pups are small, vulnerable, and not yet capable of effectively evading attack.
For example, Monterey Bay Aquarium researchers observed multiple instances of sea lions ambushing and consuming sea otter pups in central California. Out of hundreds of attacks witnessed, only a handful of pups survived thanks to last-second escapes or interventions by adult otters.
Beyond pups, there are a few records of sea lions killing solitary adult otters as well. These events are rare but demonstrate how sea lions can pose a danger, especially to less experienced juvenile otters.
In captivity, predation risk seems minimal. Zoos and aquariums housing sea lions and otters in close proximity report peaceful coexistence in nearly all cases.
Still, wild otter populations remain vulnerable to opportunistic sea lion attacks. Continued habitat monitoring and conservation efforts are needed to preserve the balance of these unique species along the Pacific coast.
Why Predation Happens
Lack of Preferred Prey Near Breeding Colonies
Sea lions rely on fish, squid, and other marine life near their breeding colonies to feed themselves and their young. However, in some areas like the Aleutian Islands and western Alaska, there has been a decline in some key prey species near colonies, likely due to overfishing by humans or environmental changes affecting prey distribution.
With limited access to prey like pollock, Pacific cod, and Atka mackerel, the sea lions have turned to opportunistic hunting of whatever prey they can find, including sea otters. Research suggests that up to 20% of the sea otter deaths in the Aleutian archipelago since the 1990s may be a result of increased predation by hungry sea lions.
Opportunism
Sea lions are intelligent and opportunistic hunters. While they prefer to eat schooling fish and squid, they have shown the ability to adapt and take advantage of other readily available food sources like seabirds, octopuses, and even seals.
This adaptability likely explains why some sea lion individuals or groups learn to hunt sea otters.
In particular, female sea otters swimming with pups likely make for easy targets compared to faster, more agile adult otters without pups. Conservation groups have also reported incidents of sea lions ambushing sea otters hauled out on shore or even surging into the kelp beds to grab them.
Such opportunistic hunting allows sea lions to supplement their diet when preferred prey is scarce.
The Impact on Sea Otter Populations
Sea otters play a vital role in maintaining the health and stability of the nearshore marine ecosystem. However, sea otter populations have faced immense pressure from predation by killer whales/orcas in recent years.
This has had a detrimental cascading effect on sea otter numbers and the ecosystems they inhabit.
Declining Sea Otter Populations
Historically, sea otters numbered in the hundreds of thousands along the North Pacific rim. But due to the maritime fur trade of the 18th and 19th centuries, sea otter populations were hunted to near extinction.
Following legal protections in the early 20th century, sea otter numbers slowly rebounded. However, over the last few decades, growing predation by orcas has caused sea otter populations to decline again.
For example, surveying data from the U.S. Geological Survey indicates that between 1995 and 2000, the sea otter population in the Aleutian Islands dropped by over 55% as a result of orca predation. Similar significant declines have been observed in other parts of the sea otters’ range as well.
Conservationists have described the situation as “dire” and are extremely concerned about the future prospects of the species if the current predatory pressures continue.
Ecosystem Impacts
The precipitous decline of sea otters can set off a destructive chain reaction within the marine ecosystems they inhabit. As a keystone species, sea otters play an outsized role in maintaining balanced nearshore food webs.
Their presence regulates populations of sea urchins and other invertebrate grazers that can otherwise rapidly overpopulate areas and outcompete other species for food sources like kelp.
With fewer sea otters present, urchin barrens form and kelp forest ecosystems collapse. Not only does this diminish critical habitat, but the diversity and productivity of marine ecosystems also declines.
Species relied upon by seabirds, fish, marine mammals, and even humans can crash as a result of cascade effects. Clearly, ongoing sea otter population declines driven by orca predation raises serious ecological concerns.
More research is still required to fully gauge the interrelated population dynamics between killer whales, sea otters, and other species. But evidence strongly suggests the current situation is highly worrisome for the health of North Pacific marine environments.
Targeted conservation efforts focusing on restoring and protecting sea otter populations could help return balance and stability to struggling nearshore ecosystems. Maintaining resilient food webs will be key for supporting biodiversity in the era of climate change.
Efforts to Reduce Sea Otter Predation
Habitat Protections
Conservation groups and wildlife agencies have implemented various habitat protections in recent years aiming to reduce predation of sea otters by sea lions. These include establishing marine protected areas and sea otter sanctuaries in locations with large sea otter populations such as the Aleutian Islands and California’s central coast.
According to the U.S. Geological Survey, marine protected areas can effectively limit disturbance to sea otter habitats and provide refuge from predation.
For example, the creation of the Sea Otter Game Refuge in 1983 provided 411 square nautical miles of protected habitat in Alaska’s Aleutian Islands. Research suggests this contributed to stabilizing declining sea otter populations in the 1990s when killer whale predation was also a major threat.
Other protected areas have been implemented more recently – in 2014, a 59 square mile sea otter “no-go zone” was established near San Nicolas Island in Southern California to help reduce shark attacks on sea otters.
Agencies monitor sea otter populations within these protected habitats and can adapt restrictions if needed.
Food Supplements for Sea Lions
Wildlife agencies have also experimented with providing supplementary food sources, such as salmon carcasses or cod freeze-dried into “fishcicles”, for sea lion populations. The goal is to divert the sea lions away from hunting sea otters and reduce incidents of predation.
According to a recent study by the Alaska Department of Fish and Game, this approach has shown some success – feeding wild Steller sea lions with salmon carcasses reduced predation on sea otters by an average of 7.5% in studied habitats.
The cost was estimated at around $8,100 per predation event avoided.
However, some conservation groups argue that supplementary feeding programs are only a short-term solution and could lead to issues like over-reliance or population increases above sustainable levels.
Whether these programs can be implemented effectively across different regions while avoiding unintended consequences remains an open question. Overall there is no consensus on best practices, so wildlife managers tend to take a case-by-case approach based on factors like local sea lion and sea otter population sizes and budget constraints.
Conclusion
In conclusion, while California sea lions do not regularly hunt sea otters, some isolated predation events have occurred. This seems to happen when male sea lions struggle to find their preferred prey near breeding colonies.
While concerning for vulnerable sea otter populations, focused conservation efforts can reduce sea otter mortality from sea lion predation.