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Sea Otters

To say that sea otters off the west coast of North America have had a troubled history is an understatement.

Once abundant with a range along virtually the entire west coast, its fate was sealed with the advent of the maritime fur trade that continued through the 18th and 19th centuries. By 1929 the sea otter had been extirpated (made virtually extinct) from British Columbia with small colonies remaining only in parts of Alaska and California. In the 1960s and 1970s sea otters from Alaska were reintroduced into parts of their former range, with 89 released on the west coast of Vancouver Island between 1969 and 1972.

Photo: Brian Gisborne

For a long time they remained "endangered" because their population was small. Their recovery continued however, and their status was upgraded to "threatened" by the time the Canadian Species At Risk Act came into force in 2002. The Act establishes Schedule 1 as the official list of wildlife species at risk. It classifies those species as being extirpated, endangered, threatened, or of special concern. Once listed, the measures to protect and recover a listed wildlife species are implemented.

The current status of the sea otter is now upgraded to one of "special concern".

There is no doubt their numbers are increasing. The most recent population study, completed in 2008, indicated just over 4,700 sea otters in British Columbia, up from approximately 3,200 in 2004. Their population now ranges along much of the exposed west coast of Vancouver Island and parts of the central mainland BC coast. They are not migratory, they occupy pretty small home ranges, maybe tens of kilometers of coastline, live 10-20 years, and generally speaking stay in a defined home area for their entire lives.

So if they have made a successful comeback, why study them?

One scientist who knows sea otters very well is Linda Nichol, a research biologist working out of the Pacific Biological Station in Nanaimo, British Columbia.

"We study them," notes Ms. Nichol, "Because they are an important part of the marine ecosystem and maintaining up-to-date information about the population supports Fisheries and Oceans Canada's (DFO) mandate to study, conserve and protect aquatic ecosystems."

Ms. Nichol and her colleagues are typically out in the field for up to three weeks a year, sometimes more during the spring and summer, doing small boat sea otter surveys - often supported by DFO Coast Guard science ships - to obtain counts and to assess the distribution of the population so they can track trends in population growth and range.

But their work is much more than just doing head counts.

Photo: Melissa Boogaards

One of the projects she was involved in this past summer was collaborating with her American colleagues collecting observations and biological samples reflecting the condition of the sea otter population in BC in different areas in relation to near shore productivity. The project will investigate and compare these factors with several populations in the United States.

Ms. Nichol: "This May we were collecting foraging information – examining what these animals were eating. An interesting thing about these creatures is that they bring their food to the surface so that - with a powerful spotting scope - you can see what they're eating and estimate how big the prey is, how much food they are bringing up per dive, how long it takes them to handle their prey, and so on. Samples of certain fish and invertebrates were also collected and will be used to develop indicators of nearshore productivity in the areas occupied by sea otters. We were also catching otters to look at their health. To that end we collected blood samples that will be used to measure indicators of environmental stress using genomic techniques as well as measuring and weighing each animal."

What is clear is that as a keystone species feeding on invertebrates, sea otters can make a profound change to the near shore ecosystem.

Notes Ms. Nichol: "It is like a big natural experiment - removal and then re-establishment of a keystone species. The question is what happened when they were gone from the coast and what is happening on their return? It is the subject of a great deal of study and not just here in BC. Sea otters were virtually absent for over a hundred years before being reintroduced. Here in BC we are observing the subtle and not-so-subtle cascade of changes that happen in a marine ecosystem when you remove and then add back a predator like the otter."

Photo: Jared Towers

Scientists have demonstrated that during their absence some really interesting things have happened. Sea otters feed on sea urchins and other herbivorous invertebrates that graze intensively on seaweed. During the century that sea otters were absent from their historical range, sea urchin populations increased and limited the number and extent of kelp forests as a result of their grazing along the rocky coastlines. As sea otter populations recovered, sea urchin populations in the areas they occupy have decreased and with that so has grazing pressure and kelp forests are reappearing. This has resulted in a change in the shoreline ecosystem. The kelp forests are increasing nearshore productivity providing a source of food for many animals, creating habitat for fish, and slowing water currents so that larval invertebrates can settle.

All of which begs another interesting question. Which is better for the ecosystem – otter absence or otter presence? Ms. Nichol replies, "It is clear that the impact of sea otters on invertebrates can be substantial. If you look at it from a human consumption perspective then having lots of big invertebrates to catch may be desirable. But from an ecological standpoint, they are just different ecosystem states. A full understanding of the cascade effect of reintroducing otters resulting in greater kelp forests has yet to be determined. That is what makes this sort of study so interesting. An ecosystem approach, which is the approach we strive for at DFO, means we have to consider all the potential interconnections even if we don't yet know what they are all are."

The research will of course continue. Not just because the sea otter is a species that DFO is responsible for. Or because they are protected under the Fisheries Act as a marine mammal. But in the broader sense, their study is in-keeping with DFO's commitment to understand and help manage the whole marine ecosystem. In the unique case of west coast sea otters, their disappearance and reappearance is a great natural experiment that will contribute to a better understanding of the interaction of a keystone species and the ecosystem it occupies.

It is an opportunity that Ms. Nichol and her colleagues plan to take advantage of.