Growth and Survival of Apache Trout Oncorhynchus gilae apache Under Static and Fluctuating Temperature Regimes Typical of Southwestern Streams
USFWS, USFS, USGS New Mexico CFWRU
September 2008 to September 2011
Scott Bonar/Colleen Caldwell
Increased stream temperatures through global climate change and urbanization will have important implications for fishes worldwide. While some information exists on effects of elevated water temperatures on Apache trout Oncorhynchus gilae apache, less is known about effects of increased and fluctuating water temperatures over extended time periods, typical of southwestern USA desert streams. We evaluated effects of static and fluctuating temperature regimes on growth and survival of Apache trout. Using a recirculating water system, we tested static temperatures of 16, 19, 22, 25, and 28°C; temperatures that fluctuated diurnally +3°C from 16, 19, 22 and 25°C midpoints; and temperatures that fluctuated diurnally +6°C from 19 and 22°C midpoints. After 14-d acclimation at 16°C, followed by 12 d of ramping up to test temperatures and then 30-d trials, we estimated the LT50 and mean growth of Apache trout for each temperature treatment. The LT50 for Apache trout under static conditions was 22.9°C; 23.1°C under conditions exhibiting +3°C diel temperature fluctuations; and 22.9°C under conditions exhibiting +6°C diel temperature fluctuations. Growth decreased as temperatures approached the LT50. When comparing static conditions to fluctuating conditions with the same midpoint, growth was less in fluctuating conditions than under static conditions if the temperature fluctuated above 22°C. Reduced survival of individual fish, inhibited growth and changes in fish behavior caused by prolonged increased stream temperature will further affect the species. Therefore, temperature tolerance information is critical to those restoring streams for Apache trout and in identifying new stocking locations. Results were published in an MS Thesis and are currently being submitted to a journal.