Spatial and food web dynamics of non-native northern crayfish Orconectes virilis in Buffalo Lake, WA
Loffredo, John Robert
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Our understanding of the ecological niche freshwater crayfish occupy in aquatic food webs has expanded in recent decades. Numerous studies demonstrate the functional trophic role of crayfish can vary among endemic and exotic populations in lentic or lotic habitats. Numerous studies have also observed direct evidence supporting baited trap catch-per-effort as a good measure of crayfish density in lentic systems. However, aggressive behavior exhibited by large male crayfish is likely to bias baited trap CPE towards larger individuals, thus underestimating actual crayfish densities. Buffalo Lake Northern Crayfish Orconectes virilis are an important prey item for introduced cold–warmwater fishes in this temperate, oligotrophic lake in northcentral Washington State, and may buffer competitive interactions between fish species. The lack of reliable distribution and diet data for this crayfish population leaves resource managers without a comprehensive understanding of this keystone species’ role within the lake’s food web. In this study we compared standardized CPE’s between four sampling methods used to document crayfish density in Buffalo Lake, WA from 2015–2018 and we used stable isotope methods to explore the ecological interactions of Northern Crayfish in the Buffalo Lake littoral food web. Two-hundred and eight crayfish liver tissue samples were used to quantify proportional diet contributions from eight littoral sources and examined for evidence of cannibalism, temporal, spatial, and ontogenetic trophic shifts. Due to the aggressive territorial behavior of adult crayfish, high predator avoidance behavior, and inherent bias that exists across sampling methods; we found using a combination of gear types is best for estimating crayfish density in this lentic system. A multiple-source stable isotope mixing model and relative trophic positions provided evidence for an ontogenetic trophic shift between juvenile and adult Northern Crayfish. These results suggest Buffalo Lake Northern Crayfish trophic position is life-stage dependent and may impact salmonid management goals related to crayfish-buffered competitive interactions between Largemouth Bass Micropterus salmoides, Rainbow Trout Oncorhynchus mykiss, and kokanee Oncorhynchus nerka.