| dc.description.abstract | Ecologists have paid considerable attention to how and why organisms select
particular habitats. Of fundamental importance is discerning which physical factors of
the environment restrict the occurrence of organisms to particular habitats. A recent
habitat suitability model (HSM) for walleye (Sander vitreus) hypothesized that light is
the primary controlling variable influencing the spatial and temporal dimensions of
feeding habitat. To test the HSM and evaluate the optical and thermal characteristics of
walleye habitat I used telemetry to estimate the foraging activity of 24 walleye in two
lakes with different water clarity, during periods of changing light intensity. The water
clarity in the lakes differed (mean Secchi depths = 2.4 m and 4.8 m); however, the
thermal environment, although variable, did not differ consistently between the lakes.
Walleye in the stained lake occurred in warmer (mean temperature = 17.0 to 19.0 C),
shallower (median depth = 3.3 to 7.4 m) water, close to the depth range predicted by the
HSM. In contrast, walleye in the clear lake were generally located at depths (median
depth = 5.5 to 8.2 m) approximately 8.0 m shallower than predicted by light levels alone
(approximately 14.0 to 19.0 m), likely because predicted optimal light levels occurred at
depths where the temperature was too cold (approximately 7.0 to 9.0 °C). The individual
activity was highly variable, but the general pattern of behaviour was similar between the
two lakes. Walleye activity tended to be low in the afternoon and increased as light
levels declined at dusk (i.e., mean change in displacement rate = 35 % between 3 and 5
pm, and 550% between 7 and 9 pm). My results support the hypothesis that subsurface
light conditions are a key element of walleye feeding habitat; however, other factors,
such as water temperature, submerged structure, and prey-fish behaviours also appear to
strongly influence walleye behaviour and distribution. Lake-specific changes to walleye
habitat may be the result of predicted changes to water clarity due to exotic species, land use
practises, and global warming. | |
