If you have ever been exploring the shoreline of SḴŦAḴ | Mayne Island and seen a small mammal scurrying along the beach, or swimming in the water, you likely came across a North American river otter. River otters are a semi-aquatic species with thick, water-repellent fur that keeps them warm when in and out of the water. They are part the weasel family, a diverse group of carnivorous mammals which also includes minks, ferrets, martens, and sea otters. 

Habitat and Behaviour

Despite their name, river otters rely on both freshwater and marine ecosystems for food. Marine-foraging river otters, like those seen on the coastlines of the Salish Sea, enjoy a diet full of fish, crabs, birds, small reptiles, aquatic insects, and more. Their fast metabolisms make them voracious eaters, so they eat a lot to keep up their energy. At an average length of 3 to 4 feet, river otters are shorter and thinner than sea otters, who can grow up to 5 feet. Their distinctive streamlined body, paired with a long tail, webbed toes, and short legs, make them efficient and powerful swimmers who can dive to 18 m (60 feet) deep when foraging!

Northern river otters have an impressive habitat range throughout North America, largely due to their ability to live in so many types of aquatic habitats. A body of water, plenty of food sources, and somewhere to establish a den is all they need. While den locations vary, river otters often use hollow logs, piles of boulders, or even the abandoned burrows of other animals such as beavers. These shelters are used for protection from the elements, for giving birth, and for raising young.

Photo by Yves Tiberghien

River otters live approximately 10-15 years in the wild, making them a long-lived species. At around two to three years of age, female otters will start having litters of up to five young, but the average is usually lower. Pupping season ranges from March to May, and it is important to take extra care not to disturb them during this exciting time.

One of the most fascinating facts about river otters is that they use a reproductive strategy called “delayed implantation” which means that even though mating occurs in the spring, the embryos don’t begin to develop until the winter. After a gestation period of two months, the young are born in the spring and have half a year to grow and learn “how to otter” before entering the colder winter season.

Ecosystem Function and Conservation Status

Since marine-foraging river otters spend time both in the ocean and on land, they play an important role in transferring nutrients from the water to plants on shore. By leaving scraps and droppings behind after a meal, they help feed terrestrial vegetation in the ecosystem and assist in the dispersal of species when seeds hitch a ride on their fur.

As such an important species on our coast, it is important we value river otters’ presence and ensure that they continue to have healthy habitats to forage, rest, and play in. While the population is currently stable, it took several decades for populations to recover following over-harvesting in the late 1800s. These days, threats to population health are more likely to come in the form of habitat loss and disturbance from land development, environmental pollution, and climate change.

Photo by Christopher Lakusta

Living Alongside River Otters and Preventing Conflict

Occasionally human-made structures such as docks, porches, and sheds are chosen by river otters as den sites, especially if they are close to a body of water. This behaviour has occasionally led to their reputation as a nuisance because of the discarded food and droppings they leave behind. While river otters often only use a den site for a couple nights if it is not a nursery, there are several steps you as a homeowner can take to prevent attracting otters to your home/structure:

1. Close and protect any potential openings larger than 2.5cm with hardware cloth, aluminum flashing, wooden boards, or any other strong material. If using hardware cloth to protect structures, burying it by about 6 inches can help prevent the otters from digging or pushing under it.
2. Remove access to potential food sources that may attract the otters. This includes garbage bins, pet food, compost, and especially any waste containing animal/fish remains.

If you have already found river otters denning in your home or a structure on your property, see this guide by the BC SPCA for more information about best practices for removal. The BC SPCA also operates an Animal Helpline at 1-855-622-7722 with advice on non-lethal methods to resolve the situation.

If you want to learn more about the land mammals on SḴŦAḴ | Mayne Island, check out this article: https://mayneconservancy.ca/the-smaller-land-mammals-of-mayne-island/

References

https://spca.bc.ca/wp-content/uploads/best-practices-river-otter-and-mink.pdf

https://www.canada.ca/en/environment-climate-change/services/convention-international-trade-endangered-species/non-detriment-findings/north-american-river-otter.html

https://www.seadocsociety.org/north-american-river-otter-facts

North American river otter habitat suitability and human–wildlife coexistence on Protection Island, British Columbia, Canada

https://www.nwf.org/Educational-Resources/Wildlife-Guide/Mammals/north-american-river-otter

https://www.natureconservancy.ca/en/what-we-do/resource-centre/featured-species/mammals/river-otter.html

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