Black Bass Growth Patterns in Relation to Hydrology in the Arkansas River, Arkansas

Hydrology has been documented as affecting the recruitment of sport fishes. However, the potential cumulative effects of river hydrology on fish growth have not been intensively studied. In 2004, 2005, and 2010, annual growth increments were measured for Largemouth BassMicropterus salmoidesand Spotted BassM. punctulatuspopulations from throughout the Arkansas portion of the Arkansas River. During three consecutive years (2007-2009), the lower Arkansas River experienced long durations of high water. Mean annual flows exceeded the 42-year average by 52%, with summer flows averaging 107% above normal and 29% of the days annually exceeding 2,830 m(3)/s. Using age-1-6 cohorts, we compared Largemouth Bass (n = 2,155) and Spotted Bass (n = 833) growth increments across hydrologic conditions occurring during the growth years experienced by these fish. Two-wayANOVAs using back-calculated age and growth year warm-season hydrology (classified as high, average, or low flow based on quartiles from historical April-September hydrographs) as main effects suggested significant hydrologic effects on the growth of both black bass species. A significant interaction between back-calculated age and growth year April-September hydrology for both black basses further suggested that flow affected growth differently across ages, with decreased annual growth increments detected for the age-1-3 cohorts. Decreased annual growth occurring during 2007-2009 also was consistent with a 0.5-year increase in the age at which Largemouth Bass attained 381 mmTL(i.e., the minimum length required for legal harvest) in 2010. Similarly, Spotted Bass required an extra 0.9 year to attain 304 mmTL(i.e., a common minimum length limit). Results suggested that the typically beneficial effects of high-flow years on black bass populations in large-river-floodplain systems may be dampened or non-existent in more highly regulated, impounded river systems, such as the modern-day Arkansas River.