Six super sea otter studies (all open access too)
It’s Sea Otter Awareness Week, and what better way to celebrate sea otters than to delve into some of the amazing things we’ve been learning about these furry critters over the past year? Here are six otterly super studies.
1. British Colombia sea otter numbers have been low around human settlements for thousands of years
A study by Erin Slade and colleagues at Simon Fraser University suggests that indigenous people living in what is now British Columbia, Canada, “limited” sea otter numbers near their settlements. Why? Well, the sea otters and people both loved to eat shellfish, so the people preferred to keep the sea otters out of their local shellfish spot.
The researchers built up this historical picture of sea otters by examining mussel shell size. Mussel shells tend to be bigger in areas without sea otters and smaller in areas with sea otters. So, by looking at the size of fossilised shells, the researchers could build a picture of historical sea otter distributions.
Where were those large fossilised shells found? Near ancient indigenous villages.
Where were the small fossilised shells found? Away from ancient indigenous villages.
Check the (open access) research for more:
2. Southeast Alaskan sea otters may have different diets, but they tend to eat the same thing year-round
You prefer tomato; your friend prefers cucumber. Individual diet preferences aren’t just a human thing. A study by Nicola LaRoche (USGS Alaska Science Center) and colleagues shows southeast Alaskan sea otters don’t all eat the same thing. Some sea otters, for example, favour crabs with their clams, some urchins. Generally, the sea otters stuck to the same foods year-round too. There was, however, one food that all sea otters seemed to love…butter clams!
The researchers used two methods to figure out what the sea otters were eating. One was to simply watch the sea otters. The way involved stable isotope analysis.
Stable isotopes are “non-radioactive forms of atoms,” which means the isotope never undergoes radioactive decay. Elements like carbon, nitrogen, and oxygen are stable isotopes. They’re in everything, including the things we eat. By looking at the ratio of the different stable isotopes in the things we eat, we can create a stable isotope signature of our food.
Now, here’s the really neat bit. The stable isotope signature of our food can be stored in parts of our body - teeth, hair, and (in the case of sea otters) whiskers. By comparing the stable isotope signatures in the otter’s whiskers and comparing it to potential food, they can figure out what they’re eating without having to actually watch them eat!
Want to know more? Check out the open-access study:
3. Toxins from harmful algal blooms increase the risk of sea otter cardiac disease
Harmful algal blooms—when colonies of algae grow out of control—release toxins that can end up in sea otters’ favourite food, like crabs and clams. Meghan Moriarty (University of California Davis School of Veterinary Medicine) and fellow researchers found that when sea otters eat a lot of food contaminated with the toxin called domoic acid, their chance of suffering fatal cardiomyopathy (a disease that makes it difficult for the heart to pump blood around the body) substantially increases.
Alongside the amount of contaminated food being consumed, the risk seemed to be greater for crab vs clam eaters and in younger than older otters. Four-year-old otters consuming high levels of contaminated food “had 2.3 times greater risk of fatal cardiomyopathy than an otter with low exposure, while a 10-year-old otter with high DA [dominc acid] exposure had just 1.2 times greater risk.”
Get into the nitty-gritty with their open-access study available here:
4. Alaska sea otters seem to mostly die from streptococcosis
It might be a grizzly job for some, but autopsies can tell us a lot. Kathy Burek Huntington (Alaska Veterinary Pathology Services) and colleagues examined data collected from over 780 northern sea otter carcasses recovered from Alaska. Their analysis found that 44% of the otters died from streptococcosis! Further analysis revealed that sub-adults were most affected, as were Kachemak Bay region otters.
Other causes of death include: neurologic diseases (10%), trauma (8%), nutritional diseases (7%), cardiovascular diseases (7%), gastrointestinal diseases /parasites (6%), undetermined (5%), septicemia (3%), and neoplasia (3%). Oiling, hepatobiliary, fungal, marine biotoxins, and pulmonary causes accounted for the rest.
Check out the open-access paper now:
5. Oregon, USA, could home ~4500 sea otters
Like many other locations, Oregon, USA, lost its sea otters long ago. With calls to reintroduce them, the big question is… how many sea otters should Oregon aim for? According to this study by Dominique Kone and fellow researchers, Oregon could comfortably take 4,538 sea otters (if you like confidence intervals, the range is between 1,700 and 9,000 otters).
It won’t be plain sailing for any reintroduced sea otters. The study also suggests human activities, particularly fishing and recreational activities, would overlap with much of the otters’ core habitat.
Find out more in the open-access paper:
6. Sea otters keep kelp forests going in the face of hungry urchins
It’s well known that sea urchins have ravished many a kelp forest to nothing. They can do this because their predators—sea otters and sunflower sea stars—aren’t as numerous as they once were. Sometimes these “urchin barrens” exist next to patches of kelp forests that appear to be doing quite well, like in the waters around Monterey Bay.
A study by Joshua Smith and colleagues suggests that, as a general rule, the more urchins that are available in an area, the more urchins sea otters will eat, and the more urchin predators there will be. But the sea otters aren’t going to those urchin-filled barrens. They’re staying in the kelp forests where urchin numbers are lower.
The researchers suggest sea otters aren’t eating the urchins in the urchin barrens for one simple reason. Gonads.
Urchins in the kelp forests are filled with large, energy-rich gonads that the sea otters love, whereas the urchins in the barrens are almost empty. In other words, hunting urchins in urchin barrens isn’t worth spending effort on.
Curious to know more? Here’s the open-access paper: