Hypolimnetic oxygenation effects on trout condition and growth in North Twin Lake, Washington

Abstract

ABSTRACTCross BK, Moore BC, Skinner MM. 2017. Hypolimnetic oxygenation effects on trout condition and growth in North Twin Lake, Washington. Lake Reserve Manage. 33:74–83.Summer stratification can restrict coldwater fish habitat, but we did not observe increases in trout growth or body condition when hypolimnetic oxygenation was applied to improve habitat conditions. Our study investigated the effects of hypolimnetic oxygenation in North Twin Lake (oxygenated 2009–2015 from May through Sep) on rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis) preferred habitat availability, abundance, body condition, and growth while using adjacent South Twin Lake as an unoxygenated reference. When assessing rainbow trout preferred habitat (dissolved oxygen ≥5 mg/L and temperature 13–19 C), oxygen levels were not limiting prior to oxygenation, and oxygenation did not increase preferred habitat availability. Trout abundance in both lakes remained comparable throughout oxygenation, but trout were able to move between lakes outside of summer months. Regardless of oxygenation, North Twin Lake had higher brook trout relative weights (i.e., body condition index) compared to South Twin (P = 0.0002), averaging 89.8 and 86.0, respectively. Rainbow trout relative weight differences were not observed between lakes before or during oxygenation (P = 0.1873). Prior to oxygenation, summer growth rates of rainbow trout were similar between North Twin and South Twin lakes (P = 0.9958). In 2012, growth rates of rainbow trout and brook trout in North Twin were not significantly different from South Twin (P = 0.8210 and P = 0.1474, respectively). Our results suggest that hypoxic conditions were not limiting trout growth or condition in North Twin Lake because preferred habitat volume and prey availability were not enhanced by hypolimnetic oxygenation.