Review by Dr. Murdoch McAllister identifies potential hatchery strategy
Link to study here: Interior Fraser Steelhead Hatchery Supplementation Review
A review of the risks and benefits of a conservation hatchery for Interior Fraser Steelhead by scientists at the University of British Columbia suggests there may be a way forward for steelhead runs that are teetering on the brink of extirpation.
Hatchery programs produce mixed results when they are poorly designed, but Dr. Murdoch McAllister and his colleagues approached the review without bias to learn what reliable studies say about both successes and failures.
The B.C. Wildlife Federation and its member clubs helped fund the review to learn if there are potentially effective options to recover these iconic fish.
Using multiple models, researchers evaluated the outcomes of various hatchery program methodologies that could be applied to the specific issues facing steelhead populations in the Thompson and Chilcotin River systems.
Many variables were considered, including using wild broodstock to preserve the characteristics that give the greatest chance of survival, and timing the release of juvenile fish to help them avoid predation. Simply releasing large numbers of hatchery fish and hoping for the best isn’t always a winning strategy as they draw the attention of predators such as wild birds and pinnipeds, who then scoop up so many fish that the number of wild-origin fish can be driven down even further.
But the researchers found examples of small conservation hatchery programs that offer a template for success. While there are risks associated with any hatchery program, doing nothing is no longer an option.
The Thompson and Chilcotin populations are classified as an Extreme Conservation Concern. Extirpation of these runs is imminent.
The steelhead spawning population for the Chilcotin watershed is currently just a few dozen individuals, down from 3,149 in 1985, putting it on the brink of extirpation. The Thompson River steelhead are similarly depressed with populations sinking to a few hundred fish from thousands.
Further complicating conservation efforts, Steelhead spend part of their lives in the ocean, which includes a gauntlet of risks. Exploding seal populations are driving steelhead marine survival rates to critically low levels. Ocean survival rates are likely the single biggest driver of steelhead populations.
Murdoch also warns that low spawning numbers are severely eroding the genetic diversity of Interior steelhead, which may lead to inbreeding.
A hatchery program carefully designed to supplement existing wild stocks may be their only hope. When a spawning population drops to just a few dozen fish, a single event affecting their environment such as a forest fire or a change in water temperature could push them to extirpation.
Simulations conducted during the review demonstrate that even a conservation hatchery will not turn things around if ocean survival falls below 6 per cent. Additionally, the population becomes non-viable below 1.7 per cent regardless of the hatchery program.
Only a major intervention is likely to change the trajectory of the Interior Fraser River Steelhead. A focused, cutting-edge approach to hatchery supplementation may help keep these fish from extirpation, but improving their ecological conditions, especially marine survival, is where the biggest potential returns lie.