The Lives of Otters

If you walk at night along an open marsh or riverbank, you may well come across an incredible animal. This mammal with two arms and two legs is agile enough to chase and catch a fish underwater and smart enough to use tools. There are as many as 13 distinct species of otter, but I will be focusing on two: the sea otter and the Eurasian river otter. Sea otters recently captured the hearts of millions when they were featured on David Attenborough’s Our Planet. In this piece, I will be looking at what makes otters so special, and what makes them so damn endearing.

While humans eat about 3% of our body weight in food each day, Eurasian otters can stuff in a whopping 15 to 20%. That figure goes up to 25 to 30% for sea otters! That is roughly the equivalent of an average human eating 3 bowling balls every day. Sea otters eat so much because they have an extremely fast metabolism, which they need to keep warm in the cold ocean waters. That is also the reason why sea otters have the thickest fur of any animal, with 850,000 to 1,000,000 hairs per square inch. Pleasingly, that is around 420 times thicker than human hair.

To quote Attenborough, “such a luxuriant coat requires a great deal of attention”. Sea otters must thus spend several hours a day grooming themselves to remove salt crystals and add natural oils. They also use this time to work air bubbles into their coat to provide an extra layer of insulation. This trapped air provides 4 times more insulation than the same thickness of blubber. Take that seals! Their thick, oily fur means that an otter’s skin never gets wet.

Around 90% of all the sea otters in the world can be found off the coast of Alaska. The way they eat is truly amazing. Sea otters dive down to collect crabs, sea urchins and other hard-shelled invertebrates. They also collect a rock, which they store under their armpit. The otter returns to the surface and balances the rock on their belly. They then use the rock as a tool to break open the shells and get to the sweet meat within.

Believe it or not, sea otters are also responsible for sequestering carbon, and are thus an ally in the fight against climate change. Sea otters are a ‘keystone’ species, meaning that they have a disproportionately large effect on the ecosystem when compared to other species. One effect of removing sea otters from their ecosystem is that sea urchin populations explode, devouring the carbon-storing kelp forests which the otters call home. In this way, sea otters are indirectly responsible for sequestering between 4.4 and 8.7 million tonnes of carbon each year. In other words, they sequester the same amount of carbon that would be released from deforesting an area between the size of Disney World and Washington DC every year.

Adult sea otters can grow up to nearly 5 feet! Bet you didn’t see that coming. That’s about 4 bowling pins or a little over 1 Danny DeVito. That makes sea otters the largest of all ‘mustelids’: the class of animals which includes weasels, ferrets and badgers. Sea otters are also the only mustelids which don’t produce a strong-smelling secretion from their anal glands to attract mates and mark territory. In order to stop themselves floating apart, sea otters wrap themselves in seaweed to form what is called a ‘raft’. Sea otters have been observed floating in groups of up to 1,000 individuals.

Beginning in around 1741, Russian hunters brought sea otter populations to their knees in order to sell their warm, dense fur. In the process, they completely exterminated the Stellar’s Sea Cow, a close relative of the manatee which measured 9 meters in length. That’s about half a bowling lane or a little over 6 Danny DeVitos in case you were wondering. Sea otter populations rebounded from just 50 individuals in 1914 to around 3,000 animals today. Some populations, however, are once again in decline as a result of oil pollution and habitat loss. They are currently listed as endangered on the IUCN red list.

Eurasian otters mark their territory by depositing faeces on boulders, bridge-footings and grass tussocks. These blobs of dung, known as ‘spraints’ have been used in recent years to track otter populations and find out what they eat. That is because it is very hard to observe them in the wild, since they are mainly nocturnal and largely hunt underwater. Eurasian otters are not picky. While they mainly feed on fish, the Eurasian otter has also been found to eat crayfish, frogs, insects, and even animals like ducks and rabbits.

Despite being solitary creatures, these otters have a pretty complex social life. Males (called ‘dogs’) have a rigid territory which they defend from other males, while female territories overlap. It is thought that females (called ‘bitches’) share a group range, but that each individual has a core area where they spend more than half their time. Essentially the only reason males and females meet is to mate. The male contributes nothing but sperm to the raising of young, despite cubs taking up to 13 months to become self-sufficient hunters. The nest in which the mother raises the young is known as a ‘holt’.

Otter populations have declined significantly across Europe, with the species recently becoming extinct in the Netherlands. Ireland is left as one of the last strongholds for the Eurasian Otter. Their decline was linked to the use of organochlorine pesticides, highly toxic chemicals which have made their way into the aquatic food chain. Organochlorine pesticides include DDT, the chemical at the heart of Rachel Carson’s seminal 1962 work Silent Spring. The fight against organochlorine pesticides was the catalyst for the birth of the environmentalist movement, and it is easy to see why.

Organochlorine pesticides are a form of chlorinated hydrocarbon, a group which also includes Polychlorinated Biphenyls (PCBs), an industrial chemical which has also been found in the spraints of Irish otters. More PCBs are found in the spraints of Irish otters the further east you go, since there is more industrial activity in the area surrounding the capital. Sadly, significant numbers of Irish otters are also killed on the roads, and habitat loss poses another grave threat.

While some residue from organochlorine pesticides can still be found in the spraints of Irish otters, levels are generally low. Some populations are starting to recover in the UK thanks to valiant conservation attempts, but we are very much not off the hook yet. If we are to save these adorable marine mammals, we must continue to designate riverbanks, marshes and coastlines around the world as special areas of conservation and set about the task of rewilding them. Only then may the otter’s prey return, and with it, the security of their species.

2 Comments on “The Lives of Otters

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