Linkages between white sturgeon recruitment and altered bed substrates in the Nechako River, Canada

Reconstructed recruitment was compared with the relatively limited set of anthropogenic alterations to the Nechako watercourse to identify and investigate potential causes of recruitment failure of Nechako River white sturgeon Acipenser transmontanus. Back-calculation of historic recruitment shows that recruitment was present but variable from 1946 until 1964. Subsequent to 1964 there was a rapid decline, principally in 1967, and recruitment failure has continued since that time. Flow regulation, which began in 1952 with the completion of Kenney Dam, preceded recruitment failure by 15 years and therefore flow regulation does not supply a simple unicausal explanation for recruitment failure. We propose that sediment input from an upstream channel avulsion in 1961, in combination with elevated flows in 1964 and 1967, led to alterations to riverbed substrates in critical white sturgeon habitat. Using air photos and specific gauge analysis, we identified a "sediment wave" in the upper Nechako River. The timing and location of avulsion sediments indicates that recruitment failure is most likely due to alteration of main channel substrates rather than the loss of off-channel habitat. Findings are discussed with reference to general hypotheses for recruitment failure in other white sturgeon populations.