Field Notes: The sensory world of sea otters

Are you hungry right now? Imagine that to find your next meal, you had to go into your neighborhood grocery store, locate the snack aisle, and grab a family size pack of Oreos. Doesn’t sound too hard, does it? Now imagine that all the lights are off in the store, the Oreos can move between shelves and aisles, and you have to sprint the entire time. Oh, and the store exists in a vacuum, so you have to hold your breath. That sounds a bit harder! Now imagine that just to live to the next day you had to repeat this adventure every 40 minutes for a full 24 hours…even more frequently if you took too long to find the Oreos last time.

You now have a better understanding of what daily life is like for a sea otter (Enhydra lutris)! The heat produced from digesting food, combined with a thick fur coat, keeps sea otters warm in the cold waters off the west coast of North America. This means that sea otters are in a race against time each day to find something to eat 30-100 feet under water—a typical meal might include clams, crabs, urchins, snails, mussels, and abalone. These invertebrates (animals without a backbone) typically hide from their voracious predators in rocky crevices or a few feet under heavy sand. What’s more, sea otters have to work quickly, since they can only hold their breath for 1-3 minutes on a dive. Given these constraints, how do sea otters find enough food to get through the day? What senses are they using to find prey and how do they make decisions about what to eat and what to ignore?

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Sea otter munching on a crunchy snack—a purple urchin! Photo credit: Ari Friedlaender. USFWS Permit MA186194-2

These questions relate to how an animal perceives its world. As humans, we perceive the world through the bias of our human sensory systems. To step outside of our own perception, as the 19th century German biologist Jakob von Uexküll elegantly describes, “we must first blow, in fancy, a soap bubble around each creature to represent its own world, filled with the perceptions which it alone knows. When we ourselves then step into one of these bubbles, the familiar meadow is transformed…Through the bubble we see the world of the burrowing worm, of the butterfly, or of the field mouse; the world as it appears to the animals themselves, not as it appears to us (1).” By considering another animal’s soap bubble, we might realize that its experiences are no less “right” or “wrong” interpretations of reality than our own.

So how can we step inside this metaphorical soap bubble? Although many types of questions about behavior can only be asked by observing wild animals in natural settings, fine scale measurements of sensory and cognitive ability require a controlled setting with a trained subject. Training is really just a mode of communication—a sender emits a signal intended to change the behavior of the receiver. As a graduate student at University of California Santa Cruz, I conduct cooperative animal research at the Pinniped Cognition and Sensory Systems Laboratory, where human researchers use positive reinforcement training methods to communicate with trained animals. By working cooperatively with these animals, we ask them about their sensory worlds, and  they report back to us about the presence/absence, intensity, or direction of various sensory stimuli (2-5). For example, a harbor seal can tell us that he can hear high-pitched sounds well outside the ranges of our hearing abilities (6)!

Before I started graduate school, I didn’t think being an animal trainer was important in the study of animal behavior. I feel very differently now that I’ve worked closely with a sea otter named Selka. After stranding as a one-week old pup, Selka was rescued, rehabilitated, and released into the wild by Monterey Bay Aquarium, and she lived as a wild otter for about 2 years. Due to multiple strandings during this time, Selka was ultimately deemed non-releasable by the US Fish and Wildlife Service. In 2014, she travelled up the coast to sunny Santa Cruz to become our research partner. I was not only responsible for Selka’s husbandry care and training for specific research tasks, but also for ensuring her general welfare. This meant that I carefully observed Selka, not just during our interactions, but also in the quiet moments when she wasn’t expecting food. I observed how she attended to unpredictable smells, sounds, and sights. I observed how she found hidden food in enrichment and toys, used her powerful arms and jaws to systematically destroy them to extract the food, then continued to play with the items hours after all the food was gone. I observed her caching toys and shell pieces around her enclosure, as if organizing her toys around her room. Although Selka lived in a non-natural setting, the closeness of our interactions meant that I was privy to elements of her behavior that would have been impossible to detect in the wild.

So what does it look like when a wild sea otter goes to college? We began by developing a mode of communication—a whistle that I sounded to indicate when she did something correctly, followed by a piece of clam, shrimp, or squid. We also established a foundation of trust—our interactions were centered around positive reinforcement, which included rewards, such as food, toys, and ice. Her first behaviors included coming to me when I called her name, making eye contact with me while maintaining a calm body posture, and following me as I moved around the enclosure. In a short span of time, Selka learned more than 30 behaviors, communicated via my hand and/or voice signals. She also learned to participate in complex, multi-step research tasks, and she is one of the only sea otters in the world trained to participate in sensory research (7).

 

I worked daily with Selka for two and a half years. Through our research and training sessions, I can tell you how well Selka can see, touch, smell, and taste, and I can speculate on how good her memory is. Through spending so much time together, I also can tell you her favorite toys, her favorite positions to nap in, and the consistency and smell of her poops. I can also tell you how important it is to use locknuts when assembling items for sea otters. I’ll never forget walking into the animal compound—an hour after I saw her “napping” under her haul-out platform—only to find that she was triumphantly carrying around a platform leg and pounding it against the tank walls as if it were one massive clam. Lesson learned: sea otters are crafty weasels and most definitely dexterous enough to unscrew nuts and bolts, hide them in various inconvenient locations, and look at you with the ultimate poker face.

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“Who me? I have no idea how this table lost its leg, I’ve just been napping .” Photo credit: Sarah McKay Strobel. USFWS Permit MA186194-2.

Selka is now continuing her important work as an ambassador for her species at Monterey Bay Aquarium, where she inspires and educates Aquarium visitors and acts as a surrogate mom to orphaned sea otter pups in the same program that she graduated from. As for me, I’ll be wrapping up my dissertation over the next year and moving on to the next adventure. Whatever that might look like, I’ll be taking many sea otter life lessons with me, especially the knowledge that space exists for a big heart in science. The researchers I’ve most admired are not afraid to express passion and care for their study species for the sake of “looking scientific”—the deep attention and care for the welfare of individual animals is precisely what makes for a good scientist and conservationist.

Sarah McKay Strobel is a 5th year PhD Candidate in the Ecology and Evolutionary Biology Department at the University of California Santa Cruz. Sarah McKay is broadly interested in the sensory ecology of predators and prey, considering the sensory and cognitive abilities of each that guide these interactions. Her dissertation research focuses on sea otter underwater foraging behavior in controlled and natural settings to investigate how sea otters detect, locate, and acquire benthic prey. When she is not training marine mammals, she is usually exercising outside, making chocolate chip Nutella-stuffed cookies, or marveling at the sensory world of ticks as she picks hundreds off her rescued German Shepherd, Poppy, after long hikes.

References:

(1) Uexküll, J. von (2010). A Foray Into the Worlds of Animals and Humans: With a Theory of Meaning. University of Minnesota Press.

(2) Reichmuth, C., Holt, M. M., Mulsow, J., Sills, J. M., and Southall, B. L. (2013). Comparative assessment of amphibious hearing in pinnipeds. Journal of Comparative Physiology A 199: 491-507.

(3) Ghoul, A. and Reichmuth, C. (2014). Hearing in the sea otter (Enhydra lutris): Auditory profiles for an amphibious marine carnivore. Journal of Comparative Physiology A.

(4) Sills, J. M., Southall, B. L., and Reichmuth, C. (2014) Amphibious hearing in spotted seals (Phoca largha): underwater audiograms, aerial audiograms, and critical ratio measurements. The Journal of Experimental Biology, 217: 726-734.

(5) Sills, J. M., Southall, B. L., and Reichmuth, C. (2015) Amphibious hearing in ringed seals (Pusa hispida): underwater audiograms, aerial audiograms, and critical ratio measurements. The Journal of Experimental Biology, 218: 2250-2259.

(6) Cunningham, K.A. and Reichmuth, C. (2016). High-frequency hearing in seals and sea lions. Hearing research, 331: 83-91.

(7) Strobel, S.M., Sills, J.M., Tinker, M.T., and Reichmuth, C. (2018). Active touch in sea otters: in-air and underwater texture discrimination thresholds and behavioral strategies for paws and vibrissae. In Review.

All research activities conducted under USFWS Permit MA186194-2.

 

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