Verification of the influence of hydrologic factors on crappie recruitment in Alabama reservoirs

I attempted to verify my previous published results describing the relations between reservoir hydrology and the recruitment of black crappie Pomoxis nigromaculatus and white crappie P. annularis in Alabama reservoirs. An additional 4-5 years of data were collected in 9 of the 11 reservoirs I originally examined that showed erratic recruitment. Recruitment estimates were derived from residuals associated with catch-curve regressions of age-3 and older crappies collected in spring with electrofishing and from age-1 catch rates obtained with trap nets set in the fall. In four Coosa River reservoirs that had short annual retention (reservoir volume/discharge) of 5-11 d, a previously derived hydrologic model to predict crappie year-class strength was fairly accurate when applied to additional data. Short winter (January-March) retention before crappie spawning and longer postwinter (April-December) retention when these fish hatched and were age 0 were related to increased recruitment. For the entire period, 64% of the variation in year-class strength was explained by these variables. In a reservoir with fluctuating water level (1.8 m) and longer postwinter retention (>25 d) on the upper Coosa River, short retention and higher water levels in winter were associated with greater year-class production and showed the same relation as previously described. For three of four recruitment-hydrologic relations, short retention and higher water levels in winter explained 65-70% of the variation in recruitment. In two Chattahoochee River impoundments that fluctuated in water level (greater than or equal to 1.8 m), wet winter conditions before spawning were positively related to crappie recruitment, similar to previous results. However, the relation weakens in these two impoundments after additional data were collected. Finally, in three impoundments along the Alabama and Tombigbee rivers, a previously derived hydrologic model to predict crappie recruitment was not accurate when applied to additional data. Crappie recruitment was related to hydrology in most of the Alabama reservoirs I examined and, for many comparisons, supported previous responses and results. Enhancement of crappie recruitment may or may not be feasible in those reservoirs, but these analyses have management implications that include regulations, stocking crappies, adjustment of angler expectations, and possibly water level manipulations in winter before crappie spawning.