Whirling Disease and Athabasca Rainbow Trout

Whirling disease has been detected in some Alberta watersheds, but not in Athabasca rainbow trout ranges, in spite of extensive testing (i.e.,87 sites tested in Athabasca rainbow Trout watersheds during 2016, 2017 and 2019, all tests negative for whirling disease, as of January 2020, M. Veillard, pers. comm. 22 January 2020). The parasite (Myxobolus cerebralis) can cause high levels of juvenile mortality, and rainbow trout in other jurisdictions have been particularly susceptible (Vincent 1996; Nehring and Walker 1996). No specific studies on the vulnerability of Athabasca Rainbow Trout to whirling disease have been conducted, and it is possible that native stocks of fish are more resistant than hatchery-origin stocks (Baerwald et al. 2011). However, if whirling disease is detected in Athabasca Rainbow Trout streams, it is prudent to manage the effects using information from studies on other strains of Rainbow Trout.
The stressor-response curve was derived from an Alberta trout age-class cohort model, using variable survival rates on juvenile trout (Sullivan and Spencer 2016). The population-level effects of whirling disease can be simulated at low, moderate or high levels of risk. This should be qualitatively determined using three factors; the prevalence of whirling disease in the watershed (low, moderate or high), the stream temperature (optimum of 10 0C– 150C mean warmest month = high risk, lower risk at cooler and warmer temperatures), and the gradient of the stream (low risk >4%, moderate risk 2 – 4%, high risk <2% gradient). This follows the Alberta risk assessment concepts for whirling disease (Paul and Reilly 2016). We expect that as Alberta biologists learn more about whirling disease and the key factors that influence its establishment and severity (e.g. Tubifex tubifex density, sediment type, water temperature etc.), and we have the input data to support inclusion within the Joe model, that this stressor-response curve will be refined.