September 30, 2017

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You Otter Know: The Big Bites of Little Sea Creatures

By Burke Museum

Burke Museum

Seattle, WA - A new study from Burke Museum researchers show that sea otters are not only cute, but have uniquely adapted skulls and forceful bites that allow them to eat a variety of foods.

Despite the sea otter’s popularity, it is also sadly an endangered species. Understanding more about how sea otters have adapted to their environment and what they eat is critical for their conservation. A sea otter’s survival depends on their ability to catch and eat prey. Unlike most marine mammals, sea otters don’t have the thick layer of blubber that can insulate them from the frigid waters of the Pacific Ocean. Instead, they rely on dense fur and a very active metabolism to keep warm.

This active metabolism is a driver in the diet and feeding patterns of sea otters. These animals have the ability to eat sea urchins, crustaceans, snails, and other marine invertebrates with hard shells that cannot be consumed by many other animals.

But sea otters vary across their range; there are the northern sea otters, found from the coasts of Alaska south to Oregon, and the southern sea otters of Southern California. One aspect that makes these subspecies particularly distinct is their diet. Southern sea otters act as diet specialists, meaning that they eat specific prey to counter competing for food with fellow otters, and also eat more invertebrates with hard shells than their northern counterparts. The northern sea otters don’t engage in this behavior at all, instead depleting their favorite prey and then turning to foraging on clams and mussels.

Why are these two subspecies of sea otters behaving so differently when it comes to their diets? The Burke Museum’s Curator of Mammals, Dr. Sharlene Santana, worked with UW alumnus Kristin Campbell to determine whether these differences can be traced to variation in the size and shape of the otters’ skulls and the ability of these subspecies to efficiently bite into prey.

“This type of population-level study is critical for understanding how anatomical adaptations may enable or constrain the ability of sea otters to vary their prey spectrum, partition food resources, and respond to changes in food availability. It also highlights the importance of museum specimens to help answer ecological questions.” Said Santana. 

Campbell and Santana measured the differences in size and cranial morphology across a variety of sea otter specimens in the Burke’s Mammalogy Collection. They photographed over 100 sea otter skulls to determine skull size and shape differences, and created mathematical models that allowed them to compare bite force and jaw strength between northern and southern sea otters.

Their research, recently published in the Journal of Mammalogy, led them to the conclusion that these dietary differences can’t actually be attributed to the different physical characteristics between northern and southern sea otters. However, this analysis of the sea otter skull revealed more distinctions within the species than what Campbell and Santana expected. 

The bite force of the sea otter far exceeded their expectations ­­­­— due to the sea otter’s short, blunt skulls and fracture-resistant teeth, they can generate nearly 80 pounds of force in their bite!

With these results in mind, they decided to look even deeper at potential differences within populations; that is, between male and female sea otters.

Their results suggested that male sea otters have the potential to consume harder, tougher prey than females by virtue of their skull size and shape. But do these differences between males and females give males the upper hand when feeding? 

“Not necessarily. What females lack in size, they make up for with brains! Female sea otters are more prone than males to use tools, like rocks and stones, to crack open tougher-than-usual prey, like clams.” Said Campbell.

It is likely that males are larger and generate more forceful bites due to sexual selection, and not to have an advantage over females during feeding. Males fight vigorously with each other for territory and reproductive opportunities with females, and the biggest and strongest sea otter generally wins.

"Discovering differences within populations is exciting! By understanding how morphological differences may affect feeding behavior within sea otter populations, we can understand more about this endangered species' feeding ecology."

Thanks to this research, Campbell and Santana have gained valuable insight into how the sea otter’s bite forces might allow them to each a variety of prey depending on environmental conditions. 

The public can learn more about these sea otters and get a close look at the skulls themselves at the Burke Museum’s Amazing Animals day on November 12!

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The Burke Museum is the Washington State Museum of Natural History and Culture. The Burke Museum is an active research museum that cares for 16 million geology, biology and cultural objects from Washington state and around the world, preserving natural and cultural history and generating new discoveries.

Founded in 1885 and designated the State Museum in 1899, the Burke Museum is the oldest public museum in Washington. The Burke Museum is located on the University of Washington campus, at the corner of NE 45th St. and 17th Ave. NE. Hours are 10 am to 5 pm daily, and until 8 pm on first Thursdays. Admission: $10 general, $8 senior, $7.50 student/ youth. Admission is free to children four and under, Burke members, UW students, faculty, and staff. Admission is free to the public on the first Thursday of each month. UW parking fees are $3 up to 4 hours or $15 all day on weekdays, $5 flat fee on Saturdays before noon, and free parking after noonon Saturdays and all-day Sundays. Call 206.543.5590 or visit The Burke Museum is an American Alliance of Museums-accredited museum and a Smithsonian Affiliate.

To request disability accommodation, contact the Disability Services Office at: 206.543.6450 (voice), 206.543.6452 (TTY), 206.685.7264 (fax), or email at The University of Washington makes every effort to honor disability accommodation requests. Requests can be responded to most effectively if received as far in advance of the event as possible, preferably at least 10 days.


For high-resolution photos, interviews, and more information please contact:

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