Stream inflow and predation risk affect littoral habitat selection by benthic fish

Abstract

Summary 1. We examined small, fishless headwater streams to determine whether transport of macroinvertebrates into the littoral zone of an oligotrophic lake augmented food availability for Cottus asper, an abundant predatory fish in our study system. We sampled fish and macroinvertebrates during the recruitment and growth season of 2 years, either monthly (2004) or bi‐monthly (2005), to observe whether stream inputs increased prey availability and whether variation in total macroinvertebrate biomass was tracked by fish. 2. Observations from eight headwater streams indicated that streams did not increase the total macroinvertebrate biomass in the shallow littoral zone at stream inflows, relative to adjacent plots without stream inputs (controls). The taxonomic composition of stream macroinvertebrates drifting toward the lake differed from that in the littoral lake benthos itself, although there was no evidence of any species change in the composition of the littoral benthos brought about by stream inputs. 3. Although streams made no measurable contribution to the biomass or taxonomic composition of the littoral macroinvertebrate benthos, there was substantial temporal variation in biomass among the eight sites for each of the (n = 7) sample periods during which observations were made. Variation in total biomass was primarily a function of bottom slope and benthic substrata in the lake habitats. Dominant taxonomic groups were Baetidae, Ephemerellidae (two genera), Leptophlebiidae, Chironomidae (three subfamilies) and Perlodidae, although we did not determine the specific substratum affinities of each taxon. 4. Mixed effects linear models identified a significant interaction between macroinvertebrate biomass and plot type (stream inflow vs. control) associated with fish abundance. Across the observed range of macroinvertebrate biomass, fish showed a significant preference for stream inflows, but more closely tracked food availability in the controls. For young‐of‐the‐year (YOY), a negative effect of temperature was also included in the model, and we observed lower temperatures at stream inflows. However, abundance of predatory adults affected habitat selection for YOY. Lake‐bottom slope also accounted for variation in abundance in both fish models. 5. Our results suggest that the effect of fishless headwater streams on downstream fish may not always be through direct delivery of food. In this study system, fish preferred stream inflow plots, but this preference interacted with macroinvertebrate biomass in a manner that was difficult to explain. For YOY, predation risk was related to the preference for stream inflows, although the specific factor that mitigates predation risk remains poorly understood.

Stream inflows to lake deltas: A tributary junction that provides a unique habitat in lakes

“…Brook trout show selection for sites with suitable temperatures, moving seasonally to groundwater upwellings, in a fashion similar to the use of inflow streams (Biro, 1998). Prickly sculpins appeared to use stream inflows in a Washington state lake primarily for its temperature regime and not for food inputs, but there was still some small effect of streamsupplied food, as well as some age-structured interactions within the populations (Polivka et al, 2013).…”

Habitat affinity and density‐dependent movement as indicators of fish habitat restoration efficacy

“…My study focused on restored vs. unrestored pools and thus did not compare food availability between pools of either type and riffles. However, the correlation in Chinook between the strength of affinity for pools of either habitat type and condition variation gives at least some quantitative basis worth further investigation, a two step process manifested by Polivka (2011) and Polivka et al (2013).…”

“…Individual-based models have made predictions of movement between these complementary habitat types (Railsback et al 1999, Railsback andHarvey 2002), and there is both laboratory (Reinhardt and Healey 1999) and conceptual (Reinhardt 2002, Conrad et al 2011 support for asset-protection behavior in stream salmonids. Empirical evidence is more difficult to obtain in a field setting (Bradford and Higgins 2001), and sometimes, the association between the predation risk regime and the predicted reduction in among-individual variation in condition must be first inferred from correlative data (Polivka 2011) and then confirmed with more specific field observations (Polivka et al 2013) or experiments. Increasingly consistent use of pools in habitat selection may offer the opportunity for asset protection, detectable as reduced condition variability.…”

Modeling Brook Trout Carrying Capacity in Owhi Lake, Washington, Using Bioenergetics

“…Each replicate was collected by agitating the substrate for 30 s and then sweeping a D‐frame kick‐net through the water column to collect suspended organisms (Polivka et al. ). Samples were washed into a bottle and preserved with 70% ethanol.…”

“…We estimated littoral invertebrate densities by collecting three replicates from 10 random, 25-m 2 sites across the lake. Each replicate was collected by agitating the substrate for 30 s and then sweeping a D-frame kick-net through the water column to collect suspended organisms (Polivka et al 2013). Samples were washed into a bottle and preserved with 70% ethanol.…”