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Effects of Low Summer Flow on Stream Physicochemistry, Macroinvertebrate Abundance, and Redband Trout (Oncorhynchus Mykiss Gairdneri) Condition in an Ephemeral Idaho Stream

Andrew Wymore, Travis Landon, Lydia Brown, and Dr. Chris Walser Department of Biology, The College of Idaho, 2112 Cleveland Blvd, Caldwell, ID, 83605

Intermittent rivers and ephemeral streams are the most common water bodies in many parts of the world. Yet, these ecosystems remain far less studied than perennial waterways.  Dry Creek, a small ephemeral stream in southwestern Idaho, supports a genetically pure population of redband trout (Oncorhynchus mykiss).  Our study objective was to evaluate trout response to changing physicochemical conditions and macroinvertebrate abundance as stream habitats shift from flowing, connected habitats to stagnant, isolated habitats.  From June to September 2019, we used data loggers to monitor stream temperatures and dissolved oxygen concentrations at 30-min intervals across 10 study reaches.  We measured current velocity weekly at all study reaches.  Across each reach, drifting macroinvertebrates were collected biweekly, while trout were sampled monthly.  Upon capture, trout were measured (mm) and weighed (g).  We used the Fish Condition Factor (K) to estimate fish health.  Across the study period, current velocity decreased across all study reaches.  Mean daily water temperatures (6.4-22.3 deg C) were within an acceptable range for redband trout.  On 18 days in August and September, dissolved oxygen levels fell below the critical limit for trout (6.0 mg/L).  Across all reaches, the rate of delivery of drifting macroinvertebrates (number/15 min.) was significantly lower in August than June and July (p<0.05).  Mean K for redband trout was significantly higher in July (1.25) than September (0.99) (p<0.05).  We attribute the decrease in fish condition over time to low levels of dissolved oxygen and decreased delivery of drifting macroinvertebrates brought upon by reduced stream flow. 




Additional Abstract Information

Presenter: Andrew Wymore

Institution: The College of Idaho

Type: Poster

Subject: Ecology

Status: Approved


Time and Location

Session: Poster 5
Date/Time: Tue 12:30pm-1:30pm
Session Number: 4081