Native fish species, such as bull trout, Athabasca rainbow trout and Westslope cutthroat trout, have been calling Alberta’s eastern slopes home for thousands of years.
Native fish populations are threatened by many different activities that take place in and around their waters, with the greatest threats being habitat destruction or alteration, hybridization with non-native fish species and fishing pressure.
Why do recovery stocking?
Recovery (or restoration) stocking is a tool that can be used to maintain genetic diversity by supplementing populations, and expanding the habitat range of native fish into streams where suitable habitats exist but have no fish living in them.
As populations decline in size and connectivity, genetic variability within a population can become limited. A larger gene pool supports population growth and sustainability, and provides more resiliency to these threats. Hybridization with non-native species is a greater risk as non-native fish move into native trout habitat ranges. Hybridization further depletes the gene pools of native trout populations, as hybrid offspring result from a combination of the gene pools of two different species, typically resulting in lower population resiliency. Learn more about hybridization in Westslope Cutthroat trout.
How does recovery stocking work?
Nearest neighbour populations
Remote site incubation (RSI) is one method of recovery stocking where fish are introduced into a new habitat from the nearest neighbouring population. It can also be used to supplement populations within the same stream where eggs were collected. Biologists collect eggs and milt from wild mature fish during their spawning season and fertilize the eggs with milt from male fish within the same stream. Fertilized eggs are moved to a quarantine facility at the hatchery until the eyed stage.
Eyed eggs are placed into an RSI unit, which improves survival rates by providing them consistent conditions to develop in. The alevin (young trout) hatch and swim out of the RSI unit into their new habitat and imprint on the stream so they will return there to spawn in the future.
In Alberta, RSI has been used to support Westslope cutthroat trout populations. Westslope cutthroat trout prefer habitats with cold, clean, clear and connected waters, and feed on aquatic invertebrates. Biologists have successfully introduced Westslope cutthroat trout alevin into sites outside of their current range to support a larger, more connected and genetically pure population.
Read more on RSI: Can buckets bring ‘em back? (Page 14 and 15).
Brood stock population
Another method of recovery stocking is through stocking genetically pure fish raised in fish culture facilities. In 2021, a genetically pure brood stock of Westslope cutthroat trout was established by collecting eggs and milt from several wild populations within a watershed. These eggs were cross-fertilized, and transferred to a quarantine hatchery facility until disease and genetic testing was complete. After testing, the fish were transferred to the Allison Brood Trout Station where they will be raised until they are mature and able to reproduce (in three to four years). The eggs and milt will be collected from this brood stock and offspring will be grown in the hatchery until they are ready to be stocked.
Where do we complete recovery stocking?
Recovery stocking typically occurs in waterbodies within the species’ native range in Alberta. Locations are chosen based on where fish have the best chance to survive, such as above barriers like waterfalls where hybridization is not an issue and where habitat is still intact. Waterbodies are specifically chosen based on where wild populations are limited in size and abundance, or where large-scale habitat recovery and non-native removal projects to restore or re-connect native habitat have occurred.
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Updated: Jan 6, 2023