Influence of spring runoff and water temperature on hatch date and growth of age-0 largemouth bass in a Montana reservoir
Largemouth bass (Micropterus salmoides) are a popular sport fish in Montana, USA and the Northwest, however, maintaining quality angling is difficult. Montana is at the northern extent of the largemouth bass range and low water temperatures may limit recruitment by reducing the size of fish attained while entering the winter season. Little is known about how different flow and temperature regimes influence hatch date and growth of largemouth bass in a northern reservoir environment. Such information is important for predicting good year classes or planning population enhancement measures. Two years with disparate hydrographs and water temperature regimes were compared from a Montana reservoir. High flows and low water temperatures occurred in 1997 whereas the converse happened in 1998. Age-0 largemouth bass were sampled throughout the summer and fall of both years to estimate hatch date, growth rate, body condition, and length entering the winter season. The median hatch dates were in mid-July and 5 days earlier in 1998 than in 1997. Hatching began 12 days earlier in 1998. Spawning and hatching were controlled by spring runoff and were later than reported for lakes elsewhere in northwest Montana. Growth rate was higher in 1998 (0.76 mm/day) than 1997 (0.46 mm/day) from the date mean lengths were ~50 mm to early October. Higher growth rates and longer lengths were achieved by hatching early in a year with high water temperature. Length entering into winter was greater in 1998, averaging 87 vs. 64 mm in 1997. Body condition was similar between years. Growth of age-0 fish appeared to cease by early October of both years. Growth rate had a greater effect on length of largemouth bass entering into winter than length of growing season.