It’s Complicated and It Depends: A Review of the Effects of Ecosystem Changes on Walleye and Yellow Perch Populations in North America

Abstract

Walleye Sander vitreus and Yellow Perch Perca flavescens are culturally, economically, and ecologically significant fish species in North America that are affected by drivers of global change. Here, we review and synthesize the published literature documenting the effects of ecosystem changes on Walleye and Yellow Perch. We focus on four drivers: climate (including temperature and precipitation), aquatic invasive species, land use and nutrient loading, and water clarity. We identified 1,232 tests from 370 papers, split evenly between Walleye (n = 613) and Yellow Perch (n = 619). Climate was the most frequently studied driver (n = 572), and growth or condition was the most frequently studied response (n = 297). The most commonly reported relationship was "no effect" (42% of analyses), usually because multiple variables were tested and only a few were found to be significant. Overall responses varied among studies for most species-response-driver combinations. For example, the influence of invasive species on growth of both Walleye and Yellow Perch was approximately equally likely to be positive, negative, or have no effect. Even when results were variable, important patterns emerged; for example, growth responses of both species to temperature were variable, but very few negative responses were observed. A few relationships were relatively consistent across studies. Invasive species were negatively associated with Walleye recruitment and abundance, and higher water clarity was negatively associated with Walleye abundance, biomass, and production. Some variability in responses may be due to differences in methodology or the range of variables studied; others represent true context dependence, where the effect of a driver depends on the influence of other variables. Using common metrics of impact, publishing negative results, and robust analytical approaches could facilitate comparisons among systems and provide a more comprehensive understanding of the responses of Walleye and Yellow Perch to ecosystem change.

Special Section Overview: Effects of Ecosystem Change on North American Percid Populations

“…2022; all in this special section) highlighted the complexities of multifaceted ecosystem changes and their challenge to percid management, which were also apparent in the review completed by Hansen et al. (2022). Several presentations chronicled trends in the Great Lakes and tributaries where multi‐species introductions (both intentional and unintentional), exploitation, water quality and habitat degradation, and remediation efforts have led to a complex interaction of food web, habitat, and harvest changes and their effects on percid populations (Fielder and Baker 2019; Skolte et al.…”

“…Declines in percid populations observed in some North American ecosystems over the last several decades are often generally attributed to changes in climate, nutrient loading, AISs (Hansen et al. 2022), and possibly changes in community composition (Sikora et al. 2021; Krogman et al.…”

“…A recurring theme among symposium presentations and the discussion forum was the emergence of multiple stressors in ecosystems where percid populations are changing and the subsequent difficulty in identifying mechanisms responsible for these changes (Hansen et al. 2022, this special section). Introductions of aquatic invasive species (AISs), such as the zebra mussel Dreissena polymorpha , quagga mussel D. bugensis , spiny water flea Bythotrephes longimanus , several carp species ( Hypophthalmichthys spp.…”

“…Symposium participants identified understanding the reasons for variation in direction of percid population responses to change as a significant challenge to future management decisions, and the synopsis provided by Hansen et al. (2022) specifically addressed this topic. The direction and magnitude of effects of some factors on percid populations are not consistent among all ecosystems (Hansen et al.…”

“…The direction and magnitude of effects of some factors on percid populations are not consistent among all ecosystems (Hansen et al. 2022), and historically similar ecosystems (productivity, latitude) do not appear to respond equally to landscape‐level changes (e.g., warming water temperatures; Nate et al. 2000; Hansen et al.…”