Light and Temperature: Key Factors Affecting Walleye Abundance and Production

Abstract

We used published information to determine optimum light and temperature conditions for walleye Sander vitreus (formerly Stizostedion vitreum) and then applied this simple niche definition to predict how water clarity, temperature, and bathymetry affect walleye habitat availability. Our model calculated thermal–optical habitat area (TOHA), the benthic area of a lake that supplies optimum light, and temperature conditions for walleye during an annual cycle. When water clarity is very low, little walleye habitat exists. As water clarity increases, TOHA for walleye initially increases and then declines exponentially. Optimum water clarity increases with maximum depth of the lake or, in the case of thermally stratified lakes, with thermocline depth. We tested this model by evaluating its ability to account for differences in the sustained yields of walleye fisheries on Ontario lakes. Our results demonstrate that (1) walleye harvest increases in proportion to TOHA times the square root of total dissolved solids, an index of nutrient level, and (2) optimum water clarity for walleye typically exists when Secchi depth is on the order of 2 m. These findings indicate that the increases in water clarity recently observed in the Great Lakes basin (as a result of phosphorus control and dreissenid mussel invasion) have reduced the supply of thermal–optical walleye habitat and, consequently have probably had negative effects on walleye production.

A predictive model for water clarity following dreissenid invasion

“…The water clarity model developed above was then applied to a suite of lakes in the province of Ontario, Canada using lake morphometric information and Secchi depths of uninvaded lakes (or pre-invasion measures of invaded lakes) reported by Lester et al (2004, Appendix B) in order to estimate Secchi depth following a hypothetical dreissenid invasion. We then extended this model to examine how these predicted Secchi depth values affect (i) thermal structure of lakes and (ii) Walleye yield, using models defined in the literature, as described below.…”

“…Hypothetical effects of dreissenids on mixing depths in 49 Walleye lakes in Ontario (Lester et al 2004) were assessed using an empirical model by Fee et al (1996) that relates the mixing depth to lake area and water clarity.…”

“…Effects of predicted post-dreissenid invasion Secchi depth on Walleye yield were investigated using equations presented in Lester et al (2004). Lester et al (2004) estimate…”

“…However, in the absence of more complex mechanistic models, the development of statistical-based models that incorporate at least some of the important mechanisms would be useful to understand how the establishment of dreissenids might influence a wide range of physical, chemical, and biological processes in water bodies at high risk of invasion. For example, such models could be used to predict changes in thermocline depth, stability and heat content, photosynthesis (Higgins et al 2014), and could be combined with fisheries models (Lester et al 2004) to estimate potential changes in yield as a consequence of dreissenid invasion.…”

“…As a secondary objective we apply the predictive water clarity model to existing limnological and fisheries models to demonstrate the value in extending our model to describe the potential for dreissenids to influence physical lake processes and biota. Walleye (Sander vitreus) production models were used as this species is among the most sought-after commercial and recreational species in North America (Kinnunen 2003, Fisheries andOceans Canada 2010), and has been shown to exhibit light sensitivity (Lester et al 2004). …”