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

Abstract

Citing 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.

Received March 27, 2017; accepted July 3, 2017 Published online September 18, 2017

ACKNOWLEDGMENTS

Data included in this paper were collected as part of ongoing mark–recapture programs undertaken by the NRSB (Landing River area) and MFB (Nutimik and Numao lakes) as well as environmental monitoring conducted by Manitoba Hydro (Slave Falls Reservoir). All biological sampling was authorized under scientific collection permits issued by MFB. Funding for data analysis and manuscript production was provided by Manitoba Hydro’s Lake Sturgeon Stewardship and Enhancement Program. C. Parker is thanked for map preparation. We appreciate the three anonymous reviewers for improving the manuscript.