Evaluation of Hypolimnetic Oxygenation Effects on Trout Condition and Survival

Eutrophication may lead to summertime hypolimnetic anoxia in lakes which poses a growing threat to coldwater fisheries.  Hypolimnetic oxygenation has been suggested as a means to restore appropriate deepwater salmonid habitat.  We compare coldwater fisheries of North Twin, which began summertime hypolimnetic oxygenation in 2009, to non-oxygenated South Twin Lake.  Upon oxygenation, trout immediately utilized the cooler hypolimnetic waters in North Twin.  Analysis of rainbow (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis) relative weights revealed no statistical difference between lakes throughout the April to October sampling period.  However, significant reduction in rainbow trout relative weights was noted among both lakes, while brook trout relative weights remained stable.  Catch per unit effort data from 2010 and 2011 revealed that North Twin has significantly higher annual carryover of rainbow trout stocking classes compared to non-oxygenated South Twin and significantly higher total trout catch per unit effort.  Although trout condition appears not to have been influenced by oxygenation in the short-term, our results indicate that hypolimnetic oxygenation can provide increased survival of trout, potentially leading to a greater abundance.