Extrinsic Factors Influencing Somatic Growth of Lake Sturgeon

Abstract

AbstractVariation in somatic growth of Lake Sturgeon Acipenser fulvescens has primarily been attributed to temperature (latitude), but recent studies have suggested additional complexities. Based on populations in Manitoba, Canada, a multivariate analysis was conducted to reevaluate the extrinsic factors influencing growth of Lake Sturgeon. Length at ages 3, 6, 9, and 12 and the following six explanatory variables were examined: latitude, mean annual air temperature, pH, conductivity, juvenile Lake Sturgeon density (gill‐net CPUE), and water velocity. Length‐at‐age variables were highly correlated, but considerable variation for fish of a given age was observed along the flow axes of individual rivers (and even within multibasin reservoirs). For example, fork length at age 12 ranged from 520 to 906 mm. After dropping latitude due to colinearity with both temperature and pH, a redundancy analysis based on the remaining five explanatory variables explained 79.9% of the variation in the four length‐at‐age variables. Lake Sturgeon growth was negatively correlated with both CPUE (41.2% of variation) and velocity (19.2%) and positively correlated with conductivity (14.8%). The temperature and pH variables lacked statistical significance for inclusion in a forward‐selection model, regardless of which other variables were included. Our results suggest that the influence of temperature (latitude) on Lake Sturgeon growth may previously have been overstated because habitat variation was not accounted for. Indeed, because populations exploit a diversity of river types across the species range, the discussion of growth needs to be placed in the context of habitat. Individuals from two Lake Sturgeon populations occupying similar latitudes can exhibit markedly different rates of somatic growth, with much of the variation being explained by juvenile density, water velocity, and conductivity. As Lake Sturgeon recovery proceeds, fisheries managers will need to contend with dynamic growth trajectory responses to increasing abundance, much as they would for other species.