Age-0 walleye Sander vitreus display length-dependent diet shift to piscivory

Abstract

The ontogenetic diet shift to piscivory can be energetically beneficial for fish growth and allows larger, more energetically profitable prey to be consumed. A shift to piscivory may be easier for longer individuals within a cohort due to larger gape size, and an early shift is likely advantageous, potentially leading to increased growth rates and survival. Such length-dependent ontogenetic diet shifts may explain the intracohort variability in length that is common for age-0 walleye (Sander vitreus). The objectives of this study were to describe seasonal intracohort variability in length, identify the timing of the shift to piscivory and determine if the onset of piscivory was length-dependent in age-0 walleye. Walleye initially fed on zooplankton, but shifted to piscivory during July of 2010 and June of 2011. The onset of piscivory in age-0 walleye was associated with length-dependent differences during both years, in which longer individuals within the cohort became piscivorous earlier than shorter individuals within the same cohort. Intracohort variability in length was detected and increased postontogenetic diet shift. Age-0 walleye that experience a growth advantage could benefit from increased survival and feeding opportunities.

Summer food habits and prey taxa and size electivity of age-0 white bass in a South-Central Nebraska irrigation reservoir

“…Age-0 white bass size appears to influence food habits as the occurrence of higher trophic level prey items (especially age-0 gizzard shad) were observed at !80 mm TL. Age-0 walleye within the study reservoir have been observed to display a similar ontogenetic diet shift from consuming Calanoida to age-0 gizzard shad at 47 and 77 mm (Uphoff et al 2019). However, in contrast to age-0 white bass, Uphoff et al (2019) found the entire cohort of age-0 walleye eventually shifted to piscivory and thereafter largely consumed gizzard shad.…”

“…Age-0 walleye within the study reservoir have been observed to display a similar ontogenetic diet shift from consuming Calanoida to age-0 gizzard shad at 47 and 77 mm (Uphoff et al 2019). However, in contrast to age-0 white bass, Uphoff et al (2019) found the entire cohort of age-0 walleye eventually shifted to piscivory and thereafter largely consumed gizzard shad. Age-0 gizzard shad availability is fairly consistent and not suspected to be limiting in this reservoir (Miller et al 2018b), suggesting gizzard shad would be available for age-0 white bass to consume.…”

“…However, as this study confirmed, there is potential for prey items such as macroinvertebrates and fish to be present in age-0 white bass food habits and when present these prey items may constitute a majority of the prey by weight. Fish prey has a higher energetic value than zooplankton (Cummins and Wuycheck 1971;Miranda and Muncy 1989) and the ability of some age-0 white bass to use this prey item is calorically important and may increase individual growth thereby broadening intracohort variability in length and potentially provide greater overwinter survival for the larger individuals within a cohort (Post 2003;Uphoff et al 2019). Shifts to alternative prey resources, especially those that have higher caloric potential, can be regulated by prey availability or fish size (Wu and Culver 1992;Post 2003;Uphoff et al 2019) and further investigations would be recommended to determine the role of these factors in feeding behavior of age-0 white bass.…”

“…During their first year of life, age-0 fishes consume a variety of taxa as a result of changes in growth and/or gape limitations. Commonly, exogenous feeding begins with zooplankton and then shifts to macroinvertebrates before sometimes culminating in a shift to piscivory (Post 2003;Uphoff et al 2019). While age-0 fish are initially zooplanktivorous, zooplankton can continue to be consumed throughout the first year of life and the zooplankton taxa selected for may vary depending on the size of fish and the zooplankton size and availability.…”

Shift happens: Evaluating the ability of autumn stocked walleye Sander vitreus to shift to natural prey

“…Walleye is a popular sportfish throughout North America and is often stocked to supplement and maintain populations (Barton, 2011; Ellison & Franzin, 1992; Fenton et al, 1996). Walleye undergo ontogenetic shifts during their first year critical for growth and survival (Einfalt & Wahl, 1997; Mathais & Li, 1982; Pelham et al, 2001; Quist et al, 2002; Raisanen & Applegate, 1983; Uphoff et al, 2019). Walleye begin feeding on zooplankton after endogenous feeding at about 8 mm total length (TL) before switching to macroinvertebrates (35–50 mm TL) and eventually to fish (60–80 mm TL; Galarowicz & Wahl, 2005; Mathias & Li, 1982; Priegel, 1969; Uphoff et al, 2019).…”