Larval Sampling as a Fisheries Management Tool: Early Detection of Year-Class Strength

Abstract

Larvae of black crappies Pomoxis nigromaculatus, white crappies P. annularis, and white bass Morone chrysops were sampled in 1992–1996 from Normandy Reservoir, Tennessee, with a 1 × 2-m neuston net. Larval crappies were not captured in 1992 or 1993, but densities over the remaining three years varied over two orders of magnitude. Larval white bass were collected every year, but densities also varied over two orders of magnitude among years. Larval crappies recruited to the gear at 9 mm total length (TL), but few over 15 mm were collected. Larval white bass recruited to the gear at 7 mm TL and continued to be sampled by the neuston net at lengths up to 35 mm TL. Peak larval crappie density in the neuston net samples was an accurate predictor of geometric mean number of age-1 crappies per hectare 1 year later in midsummer cove samples (r2 = 0.99, P = 0.0001). Peak white bass density in the neuston net samples was an accurate predictor of geometric mean catch of age-0 white bass in fall gill-net samples (r2 = 0.77, P = 0.05). Larval sampling of these species over a few weeks each spring in Normandy Reservoir can accurately demonstrate the presence or absence of strong year-classes much earlier and with less effort than traditional sampling techniques such as fall gillnetting or cove sampling. Early detection of year-class strength via neuston-net sampling may allow managers to predict poor year-classes early in the year and initiate remedial actions such as supplemental stocking or regulation changes in a more timely manner.