Evaluating how local- and regional-scale processes interact to regulategrowth of age-0 largemouth bass

摘要

Regional- and local-scale processes may interact to influence early growth and survival, thereby governing cohort strength. During summer through fall 1994-1996, we assessed how precipitation (a regional-scale process) and prey availability (a local-scale process) influenced piscivory and growth of age-0 largemouth bass Micropterus salmoides in five Ohio reservoirs (190-1,145 ha). We expected early growth to vary with the abundance and relative sizes of age-0 gizzard shad Dorosoma cepedianum. We collected age-0 largemouth bass and prey fishes every 3 weeks in each reservoir. In 1994, May precipitation was low (total = 4 cm), resulting in low mean daily reservoir discharge ((x) over bar(5 reservoirs) = 3.6 m(3)/s). In four reservoirs, stable water levels may have led to successful largemouth bass reproduction and perhaps an early hatch. As such, age-0 largemouth bass in these systems were abundant, consumed gizzard shed, and reached large sizes by fall (15.3 g). In 1995 and 1996, high precipitation (total > 12 cm) and high reservoir discharge [(x) over bar(5 reservoirs) = 13.8 m(3)/s(1995), 28.8 m(3)/s (1996)] in some reservoirs in May likely reduced largemouth bass abundances. Growth during these years was density dependent across reservoirs. When age-0 largemouth bass abundance was low, nonshad prey fish were consumed, and mean fall sizes were similar to those in 1994 (12.0 g). Conversely, fall weights (4.5-7.4 g) declined in reservoirs with increasing largemouth bass density. Surveying May precipitation in Ohio across 48 years revealed that conditions like those in 1994 occurred less than 15% of the time. Because gizzard shad should rarely be available and other prey fish species probably are limited, density-dependent processes should often regulate early piscivory, growth, and potentially, cohort strength in these systems.