Thesis | Seasonal variation in habitat quality for redband trout in desert and montane streams: Energetic implications for population persistence under current and projected changes

Redband trout (Oncorhynchus mykiss gairdneri) have experienced reductions in abundance and geographic range as the result of the compounding effects of habitat alteration, fragmentation, and stream-flow diversion. Redband trout in southwestern Idaho currently persist in contrasting desert and montane conditions characterized by highly differing temperature and flow conditions. I used a bioenergetic model to estimate the availability of suitable habitat for redband trout to examine their adaptability to environments that are predicted to change dramatically under climate change scenarios. I conducted monthly sampling of invertebrate drift, and habitat transects for wetted width, depth, and current velocity. Demographic surveys were conducted in July and October to assess redband trout abundance, growth rates, and overwinter survival. Desert streams consistently provided higher net energy intake (NEI) and had a larger proportion of energetically profitable habitat during the four-month monitoring period than montane streams. Fish in desert streams exhibited significantly higher biomass and a larger size structure, as well as higher growth and estimates of apparent survival. Increasing stream temperatures extended the growing season for fish occupying montane streams, but decreased habitat suitability during all months of the study period in desert streams and July-September in montane streams. Increases in stream temperature resulted in corresponding decreases in habitat suitability, with larger decreases occurring in larger fish.