Stable isotope analysis has emerged as an important tool in aquatic ecology. For fish, dorsal muscle from sacrificed individuals has traditionally been used in stable isotope studies; however, there are many instances when lethal sampling is undesirable. We evaluated the feasibility of using adipose and caudal fin clips as alternatives to muscle in stable isotope studies for five species of salmonids. Because fish size and water temperature can affect stable isotope ratios, we also determined whether fish length and sampling date affected the difference in isotope signatures between fins and muscle. Biopsied muscle plugs and fin clips were collected from rainbow trout Oncorhynchus mykiss, brook trout Salvelinus fontinalis, and lake trout S. namaycush as well as lake whitefish Coregonus clupeaformis and pygmy whitefish Prosopium coulterii and analyzed for stable isotopes of carbon and nitrogen. The isotope signatures of both adipose and caudal fins were significantly correlated (0.33 < R2 < 0.97) with those of dorsal muscle from the five salmonid species studied, and in some cases the signatures of fins did not differ from those of muscle. Fish length and sampling date occasionally had a small effect (0.042 < R2 < 0.49) on the relationship between the isotope signatures of fin and muscle. Although muscle biopsy provides a viable, nonlethal method of collecting muscle tissue from suitably sized fish, the strong relationships between the isotope signatures of fin and muscle demonstrate that fin clips should be considered good surrogates for muscle in stable isotope studies of salmonids.

Strong negative effects of introduced predatory fishes on native species are frequently reported but may not be universal. Recent research from productive lakes, for example, has documented few serious negative effects. Our objective was to determine how complex littoral habitat mediates the response of adult and young-of-year (YOY) native dace (Chrosomus spp.) and fathead minnow (Pimephales promelas) to the introduction of rainbow trout (Oncorhynchus mykiss) in productive lakes in Alberta, Canada. We first quantified inshore–offshore habitat use of native fish in stocked and unstocked lakes with heavily vegetated littoral zones. We then manipulated the presence or absence of trout and densities of macrophytes within enclosures in an unstocked lake and assessed the behavioral response of native fish. Our whole-lake comparisons revealed that adult and YOY fishes occurred in vegetated inshore areas to a greater extent in stocked relative to unstocked lakes. In the enclosure experiment, native fishes did not respond to the introduction of trout at natural macrophyte densities, but dace significantly reduced their occupation of enclosures with reduced macrophytes once trout were added. Our results suggest that complex littoral macrophyte beds provide important refuge habitat for native fishes, which can potentially mitigate negative effects associated with introductions of a piscivorous predator.

Summary 1. Rainbow Trout (Oncorhynchus mykiss [Walbaum]) is commonly stocked as a sport fish throughout the world but can have serious negative effects on native species, especially in headwater systems. Productive fish‐bearing lakes represent a frequently stocked yet infrequently studied system, and effects of trout in these systems may differ from those in headwater lakes. 2. We used a Before‐After Control‐Impact (BACI) design to determine how stocked trout affected assemblage‐level and taxon‐level biomass, abundance and average length of littoral invertebrates in a stocked lake relative to three unstocked control lakes in the boreal foothills of Alberta, Canada. Lakes were studied 1 year before and for 2 years after stocking. Because characteristics of productive fish‐bearing lakes should buffer impacts of introduced fish, we predicted that trout would not affect assemblage‐level structure of littoral invertebrates but might reduce the abundance or average length of large‐bodied taxa frequently consumed by trout. 3. Relative to the unstocked control lakes, biomass, but not abundance, of the littoral invertebrate assemblage was affected indirectly by trout through increases of some taxa after trout stocking. At the individual taxon‐level, trout stocking did not affect most (23 of the 27) taxa, with four taxa increasing in abundance or biomass after stocking. Only one taxon, Chironomidae, showed evidence of size‐selective predation by trout, being consumed frequently by trout and decreasing significantly in average length after stocking. 4. Our results contrast with the strong negative effects of trout stocking on invertebrate assemblages commonly reported from headwater lakes. A combination of factors, including large and robust native populations of forage fish, the generalised diet of trout, overwinter aeration, relatively high productivity and dense macrophyte beds, likely works in concert to reduce potentially negative effects of stocked trout in these systems. As such, productive, fish‐bearing lakes may represent a suitable system for trout stocking, especially where native sport fish populations are lacking.

Sperm-dependent asexual species must coexist with a sexual species (i.e. a sperm source) to reproduce. The maintenance of this coexistence, and hence the persistence of sperm-dependent asexual species, may depend on ecological niche separation or preference by males for conspecific (i.e. sexual) mates. We first modified an analytical model to consider both of these mechanisms acting simultaneously on the coexistence of the two species. Our model indicates that a small amount of niche separation between parental species and hybrids can facilitate coexistence by weakening the requirement for male mate preference. We also estimated niche separation empirically in the Chrosomus (formerly Phoxinus) sexual-asexual system based on diet overlap between sperm-dependent asexuals and their two sexual host species. Diet overlap between the sexual species was not significant in either lake, whereas the sperm-dependent asexual had an intermediate niche that overlapped significantly, but somewhat asymmetrically, with both sexual species. These empirical results were then used to parameterize our analytical model to predict the minimum strength of male mate preference required to maintain coexistence in each lake. Some male mate preference is likely required to maintain coexistence in the Chrosomus system, but the minimum required preference depends on the severity of density dependence. Future empirical work on understanding coexistence in sperm-dependent asexual systems would benefit from taking both niche separation and mate choice into account, and from simultaneous empirical estimates of male mate choice, niche separation, and density dependence.

We compared a rapid bioassessment protocol (Traveling Sweep Approach [TSA]) with a more conventional time intensive protocol (Composite Transect Approach [CTA]) to describe macroinvertebrates in wetlands in Alberta, Canada. We collected one macroinvertebrate sample using each protocol from 16 wetlands and compared abundance, catch per unit effort, and relative abundance between sample protocols. We also quantified and compared the logistics required to implement each protocol. The macroinvertebrate communities differed statistically between protocols for all three response variables; however, the differences were generally small and communities similar. The CTA protocol tended to yield higher variability in the samples, likely driven by the way these samples are collected and composited, which may introduce an unwanted source of variation when the primary monitoring objective is to assess effects of human activities over time and between sites. The CTA protocol also required significantly greater investment of time (ca. 50% greater processing time), money (ca. 1.9 times sample processing cost), and resources to execute (e.g., requirement for watercraft). Both protocols provided adequate characterization of macroinvertebrate communities in wetlands, but differences in variability and resources for deployment and processing are important considerations when choosing a sampling protocol. The rapid time-limited sweep protocol (TSA) appears to be a viable monitoring approach given that macroinvertebrate communities identified by each protocol were relatively similar but were collected using the TSA protocol at a lower cost.