Assessing effects of an overwinter dewatering on the egg-to-fry survival of brown trout in a Montana stream

Natural instream flow regimes are necessary for the ecological health of streams, including the maintenance of healthy fish populations. Economic interests such as agriculture, mining, and other industries remove water from streams, which can negatively affect fish populations. Wintertime diversions of water affect autumn-spawning salmonids such as brown trout and bull trout; they occur at the critical egg-to-fry development phase, possibly reducing oxygen flow to the eggs and increasing the rate of sub-gravel freezing. This study was designed to examine the effects of a wintertime industrial water diversion on redd building and egg-to-fry survival of wild brown trout in Warm Springs Creek, Montana. To measure egg-to-fry survival, I counted fertilized brown trout eggs into mesh-lined baskets and placed these baskets into 6 artificial redds in Warm Springs Creek. While the eggs were developing in the gravel, I measured parameters that are critical to egg development and survival and that could be affected by dewatering. In April, after the hatch, I removed the baskets and tallied the number of live fry, dead fry, live eggs and dead eggs. Survival rate was compared across years and the measured parameters were statistically analyzed to determine whether any of them had a significant impact on survival. There was no autumn or winter dewatering during the course of this study, so I cannot comment on the effects of a dewatering. Some interesting baseline patterns did emerge. The survival rate for the first two years was similar, 41% and 35%. Survival was significantly lower the third year, measuring only 8%. This may be due to a longer, colder winter the third year. The colder it was within the study redds, the more fish died. Also, the lower the water level, the colder it was within the redds. These patterns indicate that a drawdown or dewatering could increase egg mortality.

Name thesis:degree_name

Master of Science (MS)

Grantor dc:publisher

University of Montana

Year

2010

Author dc:creator

• Torrens, Christa Lyn

• artificial redds
• egg-to-fry survival
• groundwater
• Salmo trutta
• wintertime diversion

Repository record dc:identifier

https://scholarworks.umt.edu/etd/59

OAI identifier oai:identifier

oai:scholarworks.umt.edu:etd-1078