INFLUENCE OF SPRING AND SUMMER WATER TEMPERATURE ON BROOK CHARR, SALVELINUS-FONTINALIS, GROWTH AND AGE STRUCTURE IN THE FORD-RIVER, MICHIGAN

The influence of late spring and summer water temperatures on brook ch arr, Salvelinus fontinalis, growth and age structure was evaluated fro m 1984 to 1991 in the Ford River, Michigan. Temperature was monitored and brook charr sampled for vital statistics from late May through Sep tember using fyke nets and weirs at four locations within a 25.8 km se ction of stream. Scale analysis was used to determine captured brook c harr age, past length at age and relative annual growth rates. Late sp ring and summer water temperature patterns varied between years with t he greatest variability occurring in May and June. Age and size struct ure also varied between years and was significantly related to tempera ture. Years with cooler late spring and summer temperature patterns we re dominated by older (age 2 and 3), larger brook charr, while years w ith warmer spring and summer temperature patterns were dominated by yo unger (age 1), smaller brook charr. Spring and summer temperature did not appear to have a significant effect on the growth of age 0 or age 1 brook charr. However, temperature was negatively related to brook ch arr growth from age 2 on. As spring and summer water temperatures are critical to brook charr growth and survival, it is important that a st reams thermal regime be considered when establishing management goals for this species.