Habitat Quantity Required to Support Self‐Sustaining Lake Sturgeon Populations: an Alternative Hypothesis

Abstract

AbstractCiting the capacity of anadromous sturgeon species to undertake lengthy spawning migrations, Auer (1996) hypothesized that a minimum of 250–300 km of barrier‐free lake and river habitat might be required to support self‐sustaining populations of Lake Sturgeon Acipenser fulvescens. Twenty years later, the biological understanding of this potamodromous species has improved considerably, but there has been minimal effort to reconcile the barrier‐free hypothesis with the persistence of Lake Sturgeon populations in impounded habitats and improve the understanding of what constitutes a functional population‐level habitat unit for this species of conservation concern. Herein, POPAN mark–recapture models and sequential length‐frequency histograms were used to examine contemporary Lake Sturgeon abundance and population trajectories in three small reaches (230, 50, and 10 river kilometers [rkm]) of the Nelson and Winnipeg rivers (Manitoba), developed for hydroelectric power generation. Approximately two decades after harvest closures, results indicate that population recovery is occurring in all three reaches examined. Mechanisms other than in situ reproduction or recruitment (i.e., stocking and immigration) for increasing abundance are confidently discounted. Based on these results and other observations of contemporary persistence of Lake Sturgeon populations in impounded environments as well as recent genetic observations indicative of historical population structuring along the flow axes of naturally fragmented Boreal Shield rivers, it is contended that the barrier‐free hypothesis should no longer be cited as a “rule of thumb” with regard to the habitat quantity required to support self‐sustaining Lake Sturgeon populations. Rather, the concept of an uninterrupted “spawn–drift–settle–establish” habitat sequence as the cornerstone of a functional population‐level habitat unit may have broader relevance to species recovery initiatives and management. Given appropriate geomorphologic and hydraulic conditions, Lake Sturgeon populations can thrive—and in Boreal Shield rivers likely have for thousands of years—in lake, river, or impoundment sections as small as 10 rkm.