Influence of Arkansas River Hydrology on the Resident Largemouth Bass Population

Hydrology can affect the recruitment and growth rates of sport fish populations.  Long-term electrofishing data collected in the Arkansas River’s Lake Dardanelle from 1991-2009 suggested a strong inverse relationship between largemouth bass Micropterus salmoides catch per unit effort (CPUE) and mean adjusted flow from the previous year.  This relationship suggested a probable link between largemouth bass recruitment and Arkansas River hydrology.  However, the cumulative effects that river hydrology may have on growth throughout the life of a cohort have not been intensively studied.  In 2004, 2005, and 2010, annual growth increments were generated using largemouth bass (n = 2,201) collected from throughout the Arkansas River within Arkansas.  Between sampling periods, the lower Arkansas River experienced hydrological extremes during three consecutive years (2007-2009), with 29% of the days annually exceeding 2,800 m³/s.  Using age-1 through age-6 cohorts (n = 2,121), largemouth bass growth increments were positively correlated with growth years (March through February) containing longer durations of lower flows (<425 m³/s).  Conversely, annual growth increments of largemouth bass were negatively correlated with growth years containing sustained periods of higher flows (>1400 m³/s).  Two-way ANOVA analyses using backcalculated age and growth year classifications (i.e., high, medium, and low flows) as main effects also suggested significant (P<0.05) hydrologic effects on growth, with significantly smaller growth increments detected during growth years that exhibited the highest flows (typically above 1850 m³/s).  Significant (P<0.05) interaction between backcalculated age and growth year classifications further suggested that flow affected growth differently across ages, with more pronounced effects on the age 1-3 cohorts.  Decreased annual growth occurring during 2007-2009 was consistent with detectable decreases in mean total length in 2010 compared to the 2004-2005 period.  Age-4 and age-5 cohorts were significantly (P<0.05) smaller than corresponding cohorts from 2004 and 2005, with weight differences being more dramatic.  Additionally, total CPUE was 50% decreased in 2010 compared to 2004-2005, which was driven by weak 2007 and 2008 year classes that were likely related to above-average flows.  Results presented here suggest that high-flow events that are typically beneficial to largemouth bass populations in large river-floodplain systems may be dampened or non-existent in more highly regulated, impounded river systems such as the Arkansas River.