Every fall, chum salmon spawning in the Yukon’s Fishing Branch River serve as mobile messengers from the deep ocean. When they die, their rotting carcasses release a bounty of nutrients into the Arctic ecosystem.
But new research there is pointing out that salmon also deliver less desirable products to this remote region.
The salmon have spent most of their lives in the North Pacific Ocean where they accumulate about 95 per cent of their biomass, and pick up a few contaminants as well.
“You are getting a great input of nutrients as salmon die after spawning,” says Angelina Buchar, a graduate student at the University of Ottawa who is researching the contaminant levels. “So everything in the ecosystem benefits, but some of those benefits might be offset by contamination.”
In 1999, when the Vuntut Gwitchin First Nation, along with the Yukon government, established a park protecting the Fishing Branch Watershed, they named it Ni’iinlii Njik, meaning “where fish spawn.”
Now the Fishing Branch River is perhaps best known for the scores of grizzly bears that converge to feed on the spawning salmon, creating a scene more reminiscent of coastal Alaska than an Arctic river. Nowhere else are grizzly bears known to gather in such large numbers at such a high latitude.
However, large quantities of pure water, along with dissolving limestone, are the real keys to this system. Underground formations of porous rock known as karst serve as a vast aquifer, storing water in summer when it is plentiful, and releasing it throughout the year, helping to keep winter at bay in this northern clime.
Rich with calcium, the water also pumps nutrients into the system which feed everything from forests to fish eggs. “The Fishing Branch is quite a unique oasis,” says Buchar. “Arctic ecosystems are considered to be very nutrient poor. The nutrients are not there, and the water is not there. “
But the Fishing Branch has both; what’s more, the first 15 kilometres of the river remain open year round. “For a river at that latitude, that is something that catches a person’s attention,” says Buchar. “It is not surprising that there is an important population of grizzly bears there. It’s an isolated ecosystem that is well fueled with water and nutrients. “
Buchar is working with Ian Clark, a University of Ottawa professor who has been studying the unique hydrogeology at Fishing Branch for many years and wanted a graduate student to look into the biological side of the system. But in addition to the bounty of nutrients delivered by salmon, Buchar also wanted to look at the contaminants they bring upstream—mainly mercury but also polychlorinated biphenyls and other persistent organic pesticides.
The positive connections between grizzly, salmon and ecosystems have been well-documented in places like British Columbia, showing how salmon carcasses are an important source of nutrients, mainly nitrogen, phosphorus, and carbon. When bears catch fish and toss the carcasses onto the river banks, they help disperse those nutrients away from the confines of the river.
“I like to call this nature’s way of bringing nutrients back into the upstream ecosystems,” says Buchar. “It is like a natural conveyor belt of nutrients.”
Salmon accumulate 95 per cent of their biomass in the ocean where they spend most of their lives. The chum salmon in the Fishing Branch have spent four to five years in the Bering Sea and the North Pacific Ocean before swimming thousands of kilometres up first the Yukon and Porcupine rivers before branching off into the Fishing Branch.
It has been known for decades that wind can transport contaminants far from the places they are used. In the Yukon, bans have been placed on eating certain fish livers because they were so contaminated with organic pesticides and other contaminants used in other parts of the world.
Looking at “biological vectors” such as migrating animals is a newer field of study. Last summer Buchar collected samples of sediments, plants and animals from the Fishing Branch area. They included microscopic plants such as phytoplankton and an array of aquatic animals such as caddis flies and mayflies.
In order to see how mercury spreads through the food chain, she collected other fish such as slimy sculpin and arctic grayling. As a control for her research, she also collected samples from another northern river, the Blackstone River in the Peel watershed, which does not have spawning salmon.
While she has only begun her analysis, she does not think that the mercury levels found in the Fishing Branch area will be alarming.
“Yes it is a spawning stream ecosystem and other spawning rivers have measured considerable contaminants, but in the case of Fishing Branch, it is also unique in that chum are considered the least contaminated of the Pacific salmon species.”
Contaminants are stored in fat, and chum salmon are not as fatty as sockeye and chinook.
“This system is still pretty pristine. The carcasses will have a certain level of contamination, but it could be lower than other systems.”
For more information on this research, contact Angelina Buchar at angelinabuchar@gmail.com.
This column is co-ordinated by the Northern Research Institute at Yukon College with financial support from Yukon Department of Environment and Yukon College. The articles are archived at www.taiga.net/youryukon