Brain lesions, sea lice and food shortages in the Pacific have been identified as the three "most likely" causes of last years reduced sockeye salmon stocks by the Department of Fisheries and Oceans (DFO).
The Commission of Inquiry into the decline of sockeye salmon in the Fraser River has revealed salmon numbers have been declining steadily for the past 10 years and while the economic effects are easy to calculate, the ecological effects are harder to visualise.
The annual spawning of salmon occurring in the creeks and rivers of western Canada is an essential part of the salmon life cycle. It also provides an important food source for species such as bears, wolves and eagles.
Scientists have used a technique called stable isotope analysis to track the flow of nutrients from consumed and decomposing salmon from the aquatic environment to the areas surrounding salmon runs - and the results are fascinating.
Dr. Chris Darimont has used this technique to study the relationship between salmon, wolves and bears in projects funded by the Raincoast Conservation Foundation and the National Science and Engineering Council of Canada.
He explains these stable isotopes as "chemical tracers found in any organism (or their parts, like hair) that allow us to estimate how much of their foodcame from the ocean and how much from land."
Looking at the ratio of stable isotopes in an animal or plant can then show if an organism has utilised nutrients from a marine background - in other words, if they have utilized nutrients brought from the ocean by the salmon.
This technique has been used on a number of different species. Insects and birds, including songbirds, have been found to utilise salmon nutrients.
Songbirds do not eat salmon, but obtain the nutrients by eating invertebrates that eat the fish. Nutrients from salmon have been found in a variety of vegetation surrounding salmon runs including old growth trees, plants, mosses and liverworts.
Changes in salmon numbers from year to year therefore affect the productivity and biodiversity of the forests as well as the abundance of birds and animals that feed on the carcasses - such as the bald eagles that bring visitors to the Squamish area.
Given the key role that salmon play in coastal ecosystems, a more holistic approach to regulating salmon stocks may be needed, which Darimont refers to as sharing the salmon.
"Fisheries models still follow a maximally exploitative model that leaves no allocation for the hundreds of other species with which we share salmon," said Darimont.
Perhaps change is in the air. As reported in the Globe and Mail Monday Nov. 1, it was revealed to the Commission of Inquiry into the decline of sockeye salmon in the Fraser River that the DFO would be restructured to place more emphasis on ecosystem management.
