Assessing effects of supplemental feeding and Threadfin Shad addition to recreational fishing ponds using stable isotope analysis

Abstract

Pond enhancements are commonly used to increase fish production or enhance angling opportunities, but their effects are often not evaluated. I used stable isotope analysis to estimate the contribution of different rates of pelleted feed to Bluegill Lepomis macrochirus reproduction and ultimately to Largemouth Bass Micropterus salmoides growth in both the presence and absence of Threadfin Shad Dorosoma petenense. Two approaches were used: a controlled small pond experiment and sampling of established ponds. For the controlled small pond experiment I stocked 10 0.1-ha ponds with Bluegill and Largemouth Bass in February of 2012, and fed them one of five feed rates (0, 1.3, 1.9, 3.2, and 4.4 kg – ha-1 d-1, 2 ponds per feed treatment). Ponds were sampled through the summer and harvested in August. I also sampled 30 established ponds, 10 with neither Threadfin Shad or pelleted feed, 10 that received only pelleted feed, and 10 that received pelleted feed and contained Threadfin Shad. As expected, Bluegill growth and reproduction increased with increasing feed rates in the small pond experiment. The nitrogen isotopic signatures differed among trophic levels for all species. Bluegill nitrogen isotopic signatures were negatively related with feed rates. Largemouth Bass nitrogen isotopic signatures showed similar trends to those for Bluegill at high feed rates in the controlled small pond experiment. Pelleted feed contributed to the carbon isotopic signatures of both Bluegill and Largemouth Bass across pond types in the established pond study independent of Threadfin Shad presence. Observed effects on growth and Gonadal investment of Bluegill as well as shifts in isotopic signatures of both Largemouth Bass and Bluegill demonstrated that adding pelleted feed to recreational Largemouth Bass-Bluegill ponds can influence multiple trophic levels; however, the ultimate impact of this enhancement on growth, production, and condition of Largemouth Bass requires further research.