coastal cutthroat trout
Aquatic ecologists working in small streams are challenged with the task of identifying stream habitats, the spatial distribution and temporal persistence (i.e., rate of change) of habitat, and the timing and manner in which habitats are used by stream fishes. Because temporal variation of stream habitats and the mobility of stream fishes complicate species abundance-habitat association models (Van Horne 1983), the identification of high quality aquatic habitats is often problematic. In an attempt to assess habitat quality of a stream network in western Oregon, we evaluated the persistence of abundance patterns and habitat associations of coastal cutthroat trout Oncorhynchus clarkii clarkii by monitoring stream sections of high and low relative abundance for 13 months. Simultaneous habitat evaluations provided insight into factors affecting distribution patterns in main stem and tributary streams.
To investigate effects of headwater logging on downstream coastal cutthroat trout (Oncorhynchus clarkii clarkii) populations, we monitored stream habitat and biotic indicators including biomass, abundance, growth, movement, and survival over 8 years using a paired-watershed approach.
Here we evaluate the response of a headwater fish community to forest management using a before, after, control, impact (BACI) study design. Annual fish abundance and biomass estimates are from a census of pool and cascade habitat units over the fish-bearing portion of both the reference and treatment catchments. Movement, survival, and growth were estimated from the monitoring and recapture of salmonids marked with passive integrated transponder (PIT) tags. Sampling consisted of an annual electrofishing and marking event during the low-flow period (2001-2011), and beginning in the winter of 2003, there were three annual mobile antenna PIT-tag survey events in December, March, and June. Additionally, continuously operating swim-through antennas were located at the downstream end of each stream segment. The study calibration phase occurred 2001-05. Treatment-1 (2006-2008) consisted of stream adjacent logging without retention of standing tree buffers with harvest units occurring in channels upstream from channel sections inhabited by fish. During Treatment-2 (2009-2011), there was stream adjacent logging with standard buffers as prescribed by current forest practice regulations. Analysis occurred at two spatial scales, tributaries only and catchments. Overall, very few detectable changes in habitat or biologic parameters were observed in conjunction with either treatment.
We assessed use and selection of cover by coastal cutthroat trout (Oncorhynchus clarkia clarkii) in six headwater streams in three watersheds in western Oregon, USA during the summer low flow period from 1 August and September 30, 2007. We tagged 1037 coastal cutthroat trout (>100 mm) with passive integrated transponder (PIT) tags across all streams. Selection of cover was analyzed by comparing characteristics of locations used for concealment by relocated fish relative to characteristics of randomly available habitat that could be used for concealment. We measured habitat characteristics for 190 relocated individual fish using cover and 797 randomly points potentially available as cover. Of the latter points, only 235 of 797 were potential cover, based on characteristics of cover actually used by fish. Coastal cutthroat trout used substrate as cover (78%) more often than all other cover types combined (22%). Availability of different cover types was variable, but overall substrate made up 92% of available cover and the remaining 8% represented all other cover types combined. Habitat characteristics measured for both used and available cover included depth at fish location (cm), surface area of cover (m2), proximity to depth of 20 cm for fish located in < 20 cm in depth, b-axis (mm) for substrate >2 mm, and distance under substrate. Each of these habitat characteristics was different for used and available cover.
In the Pacific Northwest ecoregion of North America, sculpins represent a major constituent of freshwater assemblages in coastal rivers. Little is known of their interactions with co-occurring species, such as widely studied salmon and trout (salmonines). In this study, I evaluated inter- and intraspecific interactions involving cottids (Cottus sp.) and coastal cutthroat trout (Oncorhynchus clarkii clarkii). I used a response surface experimental design to independently evaluate effects of cutthroat trout and sculpin biomass on growth and behavior. There was evidence of both intra- and interspecific interactions between cutthroat trout and sculpins, but the interactions were asymmetrical with biomass of cutthroat trout driving both intra- and interspecific interactions, whereas sculpins had little influence overall. Cutthroat trout biomass was positively related to conspecific aggressive interactions and negatively related to growth. Sculpin exhibited increased use of cover during the day in response to greater biomass of cutthroat trout, but not sculpin biomass. Nocturnal use of cover by sculpins was unaffected by biomass of either species. This experiment provides insights into the species interactions and the mechanisms that may allow sculpins and salmonines to coexist in nature. As cutthroat trout appear to be superior competitors, coexistence between sculpins and cutthroat trout may depend on some form of refuge.
Coastal cutthroat trout (Oncorhynchus clarkii clarkii) and cottids (Cottus spp) commonly co-occur in headwater streams in western Oregon. Little is known about the comparative trophic ecology of these species or how they respond to seasonal scarcity of resources. In this study I evaluated the seasonal variability in diets and consumption as it related to food limitation for coastal cutthroat trout and cottids. Over 340 individual diets were quantified from seasonal samples collected in May, July and September of 2008. Diet overlap was relatively low among seasons and species. Coastal cutthroat trout exhibited a more diverse diet in terms of taxonomic richness of prey and consumed both aquatic and terrestrially-derived prey, whereas cottids appeared to specialize on aquatic prey. Based on diet composition and amount consumed, all species appeared to be increasingly food limited from July to September, relative to May. However when diet composition was integrated with a bioenergetic model, coastal cutthroat trout were found to be substantially more food limited than cottids. Differences in the cost of activity between these species may explain this result. Activity costs may be higher for trout, which reside in the water column and rely on active swimming, versus cottids, which lack a swim bladder and are more benthic oriented. Results of this work suggest that cottids are dietary specialists, feeding almost exclusively on benthic prey.
Mark-recapture methods were used to examine watershed-scale survival rates of coastal cutthroat trout (Oncorhynchus clarkii clarkii) from two headwater stream networks located in the foothills of the Cascade Mountain Range, Oregon. Differences in survival were explored among spatial (stream segment, stream network [main stem or tributaries], and watershed) and temporal (season and year) analytical scales and assessed among specific abiotic (discharge, temperature, and cover) and biotic (length, growth, condition, density, and movement) factors. A total of 1,725 adult coastal cutthroat trout (>100 mm, FL) were implanted with half-duplex PIT (passive integrated transponder) tags and monitored seasonally over a 3-year period using a combination of electrofishing, portable remote tracking antennas, and stationary antennas. The effects of watershed, stream network, season, year, and fish length were the most important factors among the candidate survival models. The greatest source of variation in survival was associated with year-dependent differences among seasons. There was evidence suggesting that survival was negatively associated with periods of low stream discharge and with individual fish length. In addition, low (-) and high (+) extreme stream temperatures and boulder cover (+) were weakly associated with survival.