62: Sea Otters

Ever wondered what is scientifically the fluffiest animal? It’s this week’s animal spotlight, the sea otter! These balls of fluff are known best for being, quite frankly, adorable, but they are also pretty clever, and have had to show a lot of resilience. In this plog we will be looking at their clever behaviours, their dramatic history, and their important role in sustaining their entire ecosystem. Not too shabby for a ball of fluff. Enjoy!

Sea otters are known for being cute, but there’s a lot more to them than just fluff (Picture: Suzi Eszterhas/Minden Pictures)

Basics

Otters are a member of the Mustelidae family, broadly meaning weasels. This includes ferrets, minks, martin, badgers and even wolverines. Sea otters are one of 13 otter species, and are the heaviest of the lot.

Sea otters have a surprisingly wide range of habitats, being found in northern Japan, the East Russian Islands, the Aleutian Islands and Alaska, and right down the west coast of the U.S, once even having large populations in Mexico (more on that later). Males can weigh up to 45kg and be up to 1.5m in length, with females being a little smaller. Those that live in the cold northern oceans tend to be bigger and weigh more than their Californian cousins. The average lifespan of sea otters is 10-12 years though they have been known to live up to 25 years.

Sea otters can give birth year round, having one pup at a time, and gestation can take anything from 4-12 months as they are actually able to delay their pregnancy if they want to wait for better conditions to have their young in. Males are polygamous, mating with several females, and tend not to hang around too long. Females on the other hand are known to be exceptionally attentive mothers. They give their pups near constant attention, feeding them, grooming them, and carrying them on their stomach as the mother lies on her back in the ocean, to keep them away from the cold water. Occasionally the mother will fluff up the pup and leave it floating on the water’s surface so she can dive for food, or even wrapping it in kelp to stop it from floating away.

Females have been known to care for pups that have been orphaned, and to carry their pups for days after they have passed away. Unfortunately, with the tough conditions, especially in the Alaskan waters, pup mortality is high each year.

The range of sea otters, both historical and current. (Image: Seaotters.org)

Lifestyle

Sea otters are unique in a few different ways. They are perhaps the most water loving of their biological family, living almost their whole lives in the ocean along the coast. They don’t make any dens or burrows but sleep floating on the water in what are called rafts. These are groups of either all males or all females which effectively hold hands as they sleep to stop them from drifting apart. The raft can range from anywhere between 10 to a staggering 2000 animals, though sea otters are also quite capable of managing a more solitary lifestyle.

Especially the Alaskan and Russian populations have to deal with frigid water temperatures during much of the year. Unlike most other sea mammals, sea otters have no blubber. Instead they have the densest fur in the animal kingdom, with up to 150,000 hairs per centimetres squared. They must groom this fur regularly to keep it warm, fluffy and water tight.

Sea otters are also one of the few animals that are known to use tools. They have quite a varied diet made up of fish, crustaceans and snails. To break open foods like clams and mussels, they have been seen to dive underwater and collect a rock, then lie on their back in the water with the rock on their stomach. They then smash the shellfish they want to open against the rock on their stomach until it cracks and they can reach the food inside.

An otter using a rock on its belly as a tool to smash open a clam (Picture: Thomas & Pat Leeson/SPL)

Keystone species

Sea otters have an unfortunate historical relationship with humans. Due to having such insanely fluffy, dense fur, the 1700s and 1800s saw a lucrative market in hunting them for these furs. Hunters came from all over, and many expeditions in Arctic waters also hunted sea otters as a side trade. Russia was one of the biggest providers of sea otter pelts to the market. They started by buying the pelts from Alaskan Natives to sell on, but eventually started enslaving the Natives, using torture and holding their families hostage to force the men to hunt the otters. According to Russian estimates, during this time the Alaskan Aleut Native population dropped from 20,000 to just 2,000 people from both murder and disease brought by the Russians. Further south the Americans also took part in mass hunting of the sea otters for their fur.

Across their range, the sea otter was hunted almost to extinction, dropping from an estimated 150,000-300,000 animals, to a mere 1,000-2,000 animals by the 1900s. This had some interesting and unexpected outcomes, showing that sea otters are what are known as a keystone species. This is a species which is fundamental to the survival of their ecosystem, despite often not being obviously numerous or impactful. Sea otters showed this through their diet. One of the species which they eat is sea urchins. However, when hunting severely depleted the otter population, in some cases causing a local extinctions, there were less otters around to eat the sea urchins. This allowed the urchins to explode in number and take over the sea floor. They ate everything in their paths, including the beautiful kelp forests which many species of shellfish and fish lived in. By destroying the kelp, the habitat of many other species was lost, causing others to move away or die out. As the urchins continued to increase in number, unchecked by predation from otters, the coastal areas became barren with little life. By simply removing the otter, the whole ecosystem had collapsed.

Good news however, in 1911 Russia, Japan, the US and the UK (which then ruled Canada) agreed to a complete ban on sea otter hunting. Many thought they would go extinct but the animals managed over time to rebuild their population. Though they are still classed as endangered they have managed to return to around two thirds of their original range, though they are no longer present in Mexico. Their return led to a reduction in sea urchin numbers in some areas, after all sea otters can eat up to 1,000 sea urchins a day. This meant that the kelp forests were able to regrow and many other species return, restoring the ecosystem. The sea otter returned to a population of approximately 150,000.

Unfortunately, that is not the end of the story. In the Aleutian Islands in the last 30 years the otter population has dropped again by around 90%. This time the cause appears to be hunting by orcas, which some suggest may have switched their diet to prey on sea otters due to a lack of their traditional whale prey species, caused by a decline in whale numbers. Other issues such as oil spills and pollution have also contributed to the otter’s decline. This has allowed sea urchins to return once more. In an additional blow to the ecosystem, warming and greater acidification of the oceans caused by the high levels of greenhouse gases in our atmosphere have weakened the coral reefs there, allowing the sea urchins to demolish them more quickly and effectively than previously. The kelp forests too are being once again consumed.

Kelp forests, as shown on the left, are often teaming with life. They are a sign of a healthy underwater ecosystem in Alaska. However, if sea urchin numbers are allowed to explode, they graze everything leaving the sea floor barren of diversity as on the right (Picture: Nation Park Service)

Sea otters are caring mothers, clever tool users and their presence is critical for the health and survival of their ecosystem. They have had a dramatic history of being dragged nearly to extinction, some thinking they would never bounce back. From this they manage to rebuild their populations however, and return to their old haunts. Now they’re being faced with another decline. Hopefully with humans as their allies rather than enemies this time they can return, and remain for the long term.

For more info:

An article about the recent decline in sea otter numbers: https://www.nytimes.com/2020/09/10/science/otters-sea-urchins-alaska.html?smid=fb-nytimes&smtyp=cur

Parenting, sea otter style:

Music: kongano.com

Cover image: Mike Baird/Fickr

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