FACTORS INFLUENCING DECREASED GROWTH OF TROUT IN ASHURST LAKE

Abstract

Before 1980, Ashurst Lake had an exceptionally productive rainbow trout fishery. More recently, Ashurst has become turbid and trout growth rates have declined substantially. The growth, condition, and food habits of a single cohort of rainbow trout was followed from May 1985 until October of 1986. The first year, trout in Ashurst grew from 66 mm to 164 mm in 5 months. Growth reached an average of 24 mm/month from June to September, a time when trout fed primarily on Daphnia. By July of the second year, growth had stopped and condition declined substantially in conjunction with a change in their diet from Daphnia to crayfish and minnows. The decrease in growth rate was attributed to a decrease in the food base coupled with hampered foraging abilities of rainbow trout in water with high turbidity. High tubidity may have resulted from erosion of the surrounding watersheds.