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Abstract Cisco (Coregonus artedi) are a widespread, cold‐water zooplanktivore native to North America. Although Cisco are generally referred to as an “obligate zooplanktivore,” there is some evidence that the species exhibits considerable variability in trophic niche. Here, we assessed how Cisco body size relates to trophic position, that is, trophic ontogeny. We analysed¹³C and¹⁵N isotopes from Cisco ranging from 127 to 271 mm in body length (n = 66) from Trout Lake, Vilas County, Wisconsin, USA.¹⁵N isotopes showed smaller Cisco had a trophic position of ~3, which steadily increased to ~3.5 for larger Cisco. Further,¹³C isotope signatures showed Cisco transitioned to be more pelagically reliant (lower¹³C signatures). Using gillnet catch data, we found that larger Cisco were using deeper habitats than smaller Cisco. Our results support that Cisco have significant variability in trophic niche even though they are traditionally thought of as an obligate planktivore. Overall, we emphasize that researchers should be cautious when generalizing Cisco trophic function, particularly when considering the broader food web. 

Managing fisheries in a changing socio-ecological environment may require holistic approaches for identifying and adapting to novel ecosystem dynamics. Using 32 years of Ceded Territory of Wisconsin (CTWI) walleye ( Sander vitreus) data, we estimated production ( P), biomass ( B), biomass turnover ( P/B), yield ( Y), and yield over production ( Y/P) and tested for hyperstability in walleye yield. Most CTWI walleye populations showed low P and B, and Y/P < 1 . Yet, production overharvest ( Y/P > 1) was prevalent among Wisconsin walleye recruitment-based management approaches (natural recruitment (NR), sustained only by stocking, combination). Production, B, and P/B have declined in NR populations, while Y and Y/P have remained constant. Walleye Y was hyperstable along a production gradient among all management approaches and fishery types (i.e., angling only, angling/tribal harvest combined). Diminishing productivity and hyperstable yield may be jointly contributing to observed walleye declines. We classified lakes into management groups of low, moderate, or high vulnerability to harvest based on Y/P and P/B dynamics and identify that harvest may benefit from declines to maintain or increase the adaptive capacity of CTWI walleye. 

ABSTRACT Ecosystems are abruptly changing due to invasive species and global climate change. In lakes, invasive Rainbow Smelt Osmerus mordax can cause negative ecosystem effects through competitive and predatory interactions with native species leading to food web shifts away from native species dominance, altered zooplankton communities, and the decline or extirpation of native cool and coldwater fishes. We conducted two whole-lake removals of invasive Rainbow Smelt and simultaneous introductions of native Cisco Coregonus artedi through stocking. About 327 and 1.6 adult Rainbow Smelt/ha were removed and about 45 adult Cisco/ha were stocked over 4 years into the two experimental lakes. In one system, native Yellow Perch Perca flavscens relative abundance and density significantly increased by 556% and 143% post-manipulation, respectively. In the other system, native Walleye Sander vitreus relative abundance increased by 26% and became consistently present in the pelagic zone post-manipulation (allowing for density estimation). Rainbow Smelt relative abundance and density decreased by >85% in both experimental lakes. The two ecosystems shifted to native species dominance while invasive Rainbow Smelt became insignificant components of the food webs. In these two intensive whole-lake manipulations, we applied the Resist–Accept–Direct (RAD) climate adaptation framework to test an applicable ecological adaptation strategy and used panarchy theory as an ecologically grounded pathway to purposefully direct ecosystem transformation. We used this holistic management framework to better understand and manage undesired ecological change—“food web thinking.” In the context of our study, two ecosystems were purposefully directed towards native food web structures, species interactions, and processes, which mitigated Rainbow Smelt driven negative effects. 

Abstract Information on yellow perchPerca flavescenspopulation dynamics and responses to various abiotic and biotic factors in oligotrophic, north‐temperate inland lakes is limited. Water level fluctuations are known to influence available habitat and biological communities within the littoral zones of lakes, yet research is lacking for yellow perch in Wisconsin. The goal of our study was to characterize yellow perch population‐level responses to natural water level fluctuations in four northern Wisconsin lakes using a 39‐year time series. On average, increasing water level periods correlated with lower mean fyke net and gill net relative abundances (catch‐per‐unit‐effort), though generally not statistically significant. Yellow perch mean relative weight varied among lakes and was significantly greater during increasing water level periods for all lakes except one. The lack of statistically significant findings potentially suggests a buffering mechanism of north‐temperate oligotrophic lakes due to their small surface area to volume ratios, relative lack of nutrients, and(or) littoral structural habitat compared to other systems (e.g., shallow eutrophic lakes). Our results suggest that natural water level fluctuations may not be an environmental concern for yellow perch populations in some north‐temperate oligotrophic inland lakes.