Feeding ecology and morphometric analysis of paddlefish, Polyodon spathula, in the Mermentau River, Louisiana

Little is known about the morphometrics and the feeding ecology of paddlefish in Louisiana. I examined the morphometrics and feeding ecology of paddlefish from the Mermentau River, Louisiana from March 2002 to February 2003. Paddlefish were examined morphometrically by taking measurements of eye-fork length (EFL), body cavity length (BCL), girth (G), vent girth (VG), mouth vertical (MTB), mouth horizontal (MSS), and mouth gullet bottom (MGB) to determine which parameters would give a better estimate of weight (W). Regression analysis resulted in a morphometric model of the form: logW = 10.10 + 1.52 (logEFL) + 1.21 (logG) + 0.24 (logVG) (r2 = 0.97), though I recommended a more inclusive conservation model of the form: logW = -9.82 + 1.15 (logG) + 1.39 (logEFL) + 0.25 (logVG) + 0.15 (logBCL) (r2 = 0.97). Reanalysis of range wide data revealed reservoir/lake paddlefish were generally heavier than river paddlefish at larger eye-fork lengths. This may reflect denser patches of zooplankton in reservoir/lake systems, which may allow for greater paddlefish foraging success than in rivers. Copepods and cladocerans occurred in 90% and 82% of the stomachs, respectively. Feeding seasonality peaked in summer and winter. Diet appeared to “switch” from copepods in the summer to cladocerans in the winter. Diatoms dominated most of the full May stomachs. Paddlefish diets were similar between seasons except for the summer and winter seasons. Copepods and cladocerans contributing to most of the similarities and dissimilarities. Paddlefish diets were similar between all stages of sexual maturity with copepods and cladocerans contributing to most of these similarities and dissimilarities. An evaluation of size selectivity using Chesson’s Alpha indicated non-selective feeding and thus paddlefish may be described as indiscriminate planktonic feeders. Calculations of apparent ingestion time indirectly suggest that paddlefish were able to locate dense patches of zooplankton. This study followed the Mississippi Interstate Cooperative Resource Association’s (MICRA) paddlefish studies