Anadromous Sturgeons: Habitats, Threats, and Management

<em>Abstract</em>. — White sturgeon <em>Acipenser transmontanus</em> were once abundant in the lower Fraser River of British Columbia, but have been dramatically reduced by overfishing and habitat loss. Significant efforts have been put into collecting baseline abundance and demographic data over the past decade. However, much of the population biology is still unknown, thereby limiting the ability of managers to focus conservation efforts. For example, one of the pressing questions is the importance of slough habitats, which are used by young juveniles much more than older juveniles and adults. In the absence of direct estimates of birth and death rates, a valuable alternative is to infer these rates from data on population structure using demographic models. Here, we fit an age-based model for white sturgeon to the available length-frequency data from slough and river habitats. Our analysis of the parameterized model indicates that the white sturgeon population in the lower Fraser River was declining through the 1980s and into the 1990s. We estimate a growth rate in the range of λ = 0.90 to λ = 0.96, which corresponds to a 4–10% decrease in the population each year. This estimate agrees with an independent estimate of λ = 0.91 derived using only catch-per-unit-effort data on juvenile white sturgeon from a slough habitat. Sensitivity analysis of the fitted population model reveals that juvenile survival has the largest influence on population growth. Thus, we infer that improving juvenile survival in the slough habitats is key to conserving this white sturgeon population. We feel that observational and experimental studies that focus on the survival of young juveniles will have the largest impact on our understanding of white sturgeon population biology.