Coldwater fish in small standing waters

Abstract

This chapter describes standard techniques for sampling coldwater fishes in small standing waters. Within the context of this book, coldwater fish species are those that prefer water temperatures less than 15°C, and small standing waters are lakes and reservoirs where surface area is less than 200 ha. Chapter 7 of this book describes sampling coldwater fishes in large standing waters (i.e., surface area > 200 ha). The criterion that separates small and large waters is arbitrary and does not imply that different methods are required depending on, for example, whether a lake is 199 or 201 ha. Two chapters are dedicated to sampling coldwater fishes in standing waters because lake size varies by several orders of magnitude and some differences in sampling methods are needed to achieve efficient sampling at both ends of the lake-size continuum. Although it is clear that some differences in methods are necessary to accommodate extremes in lake sizes, it is not clear when the transition from methods for small lakes to methods for large lakes should apply. To bridge this gap, we describe methods of sampling coldwater fish in small lakes and reservoirs that are compatible with a subset of the methods proposed for coldwater fish in large lakes and reservoirs (see Chapter 7). The method proposed for sampling coldwater fish in small standing waters is depth-stratified summer gill netting. We acknowledge that coldwater species often inhabit the same lakes and reservoirs as warmwater fish. Thermal stratification during summer influences the depth distribution of coldwater and warmwater species, and a depth-stratified survey can sample both temperature guilds. For this reason, gill-netting methods for sampling coldwater fishes have been chosen so that they are compatible with gill-netting methods proposed for sampling warmwater fishes (i.e., Chapters 2 and 3).