Big Fish, Big Trees: Sooke's Ayum Creek

Big fish in Ayum Creek.

Ayum Creek in Sooke is a good place to witness how salmon and the forest interact. Although one is a water creature that cruises the ocean's depths, and another a fixed feature of the land, these diverse species need each other.

This fern-covered Bigleaf maple greets visitors to Ayum Creek Regional Park Reserve

Most people know that salmon need both fresh and salt water during their life cycle. Less well known is that large, old trees are just as important to all seven species of salmon that have lived and died in Vancouver Island waters for 10 - 12,000 years.

Ayum creek is a small spawning stream that contains coho and chum salmon, as well as steelhead and cutthroat trout. These species are dependent on large trees in the riparian habitat along the banks, as well as large woody debris in the water to provide more structure and an improved habitat.

Evidence of this land's industrial past. There used to be an early saw mill
and log sort on the 6.4 hectare site where the park now sits.

"The abundance of coho can be limited by the number of suitable territories available (Larkin 1977). Pool habitat is important not only for returning adults, but for all stages of juvenile development. Preferred pool habitat includes deep pools with riparian cover and woody debris."

"Streams with more structure (logs, undercut banks, etc.) support more coho (Scrivener and Andersen 1982), not only because they provide more territories (usable habitat), but they also provide more food and cover. "

"There is a positive correlation between the amount of insect material in the stomachs of salmon and the extent the stream was overgrown with vegetation (Chapman 1965). In addition, the leaf litter in the fall contributes to aquatic insect production (Meehan et al. 1977)."                              

          - source

But the fish aren't the only winners. The trees and riparian habitat benefit from the nutrients found in the dead salmon. Often bears, gulls, and other creatures pull dead salmon into the forest to dine on. Uneaten portions are left in the woods.

Once there, the nitrogen in the decaying fish fertilizes the surrounding plants, including the trees, helping them reach their impressive proportions.

Researchers have reported up to 70 percent of the nitrogen found in riparian zone foliage comes from salmon. One study concluded that "trees on the banks of salmon-stocked rivers grow more than three times faster than their counterparts along salmon-free rivers and, growing side by side with salmon, Sitka spruce take 86 years, rather the usual 300 years, to reach 50 cm thick."

While there are not any giant ancient trees in Ayum Park, there are a nice selection of medium sized trees that are growing larger with the benefit of the park's protection, and the salmon's nitrogen.