The Ecology, Status & Recovery Prospects of Nooksack Dace and Salish Sucker in Canada
I studied the ecology and assessed the current status and prospects for recovery of two endangered fishes, the Salish sucker and the Nooksack dace. Salish sucker populations were located in 9 of 45 Fraser Valley watersheds. Distribution is discontinuous and abundance is spatially clumped at the regional and watershed scales. Populations are concentrated in headwaters, especially beaver ponds. The amount of deep pool habitat in a reach is the most powerful predictor of presence, but fish are usually absent if more than 50% of the land within 200 m of a reach is urban. Radio telemetry work showed that Salish suckers are crepuscular, have home ranges averaging 170 m of linear channel, made their longest movements during the spawning period (March to early June) and rarely crossed beaver dams. Relative to closely related Catostomids, they are small, early maturing, and have a prolonged spawning period. Nooksack dace are limited to three watersheds in Canada. Populations are spatially clumped. The amount of riffle habitat in a reach is the most powerful predictor of their presence, while long sections of deep pool are associated with absence. Mark-recapture work suggests that dace typically range over less than 50 m of channel, but that a small number venture further. Spawning is prolonged (April –July). Life history characteristics of both species are likely to impart good resilience to short-term disturbances of limited spatial scale, but not to the chronic, large-scale disruptions that affect their habitat in Canada. I identified eight potential threats and for each assessed species vulnerability, severity in each population’s watershed, and the ability of current legislation and policy to address it. In light of these three factors, Salish suckers appear most threatened by acute hypoxia and Nooksack dace are most threatened by lack of water. Both species have been strongly impacted by habitat destruction from drainage and infilling projects and may be vulnerable to introduced predators and habitat fragmentation. Toxicity from urban runoff, sediment deposition and riffle loss to beaver ponds (dace only) threaten individual populations, but are probably not major threats across the range.