Influence of Predation Risk on the Overwinter Mortality and Energetic Relationships of Young-of-Year Walleyes

Abstract

We investigated three potential mechanisms-size-dependent overwinter energy loss, size-specific predation, and size-dependent predator-induced metabolic costs-to determine the role of body size and predators on the overwinter survival and energy reserves of young-of-theyear walleyes Stizostedion vitreum. Walleyes were reared in outdoor hatchery ponds in Westport, Ontario, for three overwinter periods () in the presence or absence of predators (burbot Lota lota or adult walleyes). Other young-of-the-year fishes were provided as potential prey items. We predicted that (1) smaller individuals of a young-of-the-year walleye cohort would have lower prewinter energy stocks and would deplete them at a higher rate; (2) no size-dependent overwinter survival would occur in walleyes reared without predators; and (3) physiological stress, in combination with size-selective predation on smaller individuals, would lead to size-dependent overwinter mortality in young of the year reared with predators. Prediction 1 was not supported by lipid, protein, or specific-energy content data; indeed, smaller walleyes actually gained energy over the winter, whereas larger walleyes lost energy. Prediction 2 was supported but prediction 3 was not, as no significant survival differences were observed between four size-class quartiles in any pond or year. However, young-of-the-year walleyes reared over winter in the presence of predators lost significantly more weight and energy and had significantly lower lipid concentrations at the end of winter than did those reared in the absence of predators. Although no differences in overwinter survivorship were detected between young-ofthe-year walleyes reared in predator and predator-free ponds, the presence of significant predatorinduced energetic costs in the absence of size-selective mortality suggests that the size-selective mortality observed in some natural walleye populations is the direct effect of the presence of predators.

Performance of tropical fish recruiting to temperate habitats: role of ambient temperature and implications of climate change

“…Climate change may alter patterns of connectivity by increasing larval growth rates (O'Connor et al 2007, Munday et al 2008a) and altering ocean currents (Munday et al 2008a), but a certain amount of long-distance transport will remain. Thus, for the majority of tropical species, overwinter survival will likely remain the ultimate population bottleneck, as shown for fish in temperate fresh-and saltwater habitats (Ludsin & DeVries 1997, Hurst & Conover 2001, Pratt & Fox 2002, Biro et al 2004). It will, therefore, be increasingly important to understand the complex set of physical and biological factors, the interactions of which ultimately determine ecologically relevant temperature thresholds.…”

Energetics, Predation, and Ration Affect Size-Dependent Growth and Mortality of Fish During Winter

“…Because the energy demands of predators likely increase with warmer, more variable winters, winter interactions between predation and body size should intensify with declining latitude (Garvey et al 2003a). At higher latitudes, biotic interactions may also be important when cold-active predators such as walleye or trout are abundant (Pratt and Fox 2002). Although sizedependent interactions certainly are not confined to winter (Olson 1996), seasonally declining production Notes: Log e -transformed length is the independent variable or covariate in each model.…”

“…A winter pond experiment explored how adult largemouth bass, a common predator, affected size-dependent survival, growth in length, and energy condition of age-0 largemouth bass. We expected that the model would predict and the experiment would confirm that predators reduce foraging, potentially causing higher mass-specific energy depletion and mortality of small individuals (see Pratt and Fox 2002 for a similar prediction).…”

Indirect predator effects on age-0 northern rock sole Lepidopsetta polyxystra: growth suppression and temporal reallocation of feeding

“…Aphids respond to damsel bug predators by reducing time spent feeding, presumably influencing individual growth and offspring production. Suppressive effects of predators upon hard clam Mercenaria mercenaria (Nakaoka 2000), walleye Stizostedion vitreum (Pratt & Fox 2002) and juvenile pinfish Lagodon rhomboids (Harter & Heck 2006) growth have also been documented. Rock sole confined to laboratory tanks with predators and with access to food only during daylight hours, arguably had to make the best of a bad situation.…”

“…Yet, indirect, non-consumptive predator effects also have the potential to influence prey behavior, growth and ultimately, fitness (Lima 1998). While many studies have demonstrated short-term suspension of feeding in response to perceived risk, fewer have demonstrated the longer term consequence of reduced growth (Nakaoka 2000, Pratt & Fox 2002, Harter & Heck 2006. By amputating damsel bug (Nabis spp.)…”