Reservoir Ranching of Paddlefish

Abstract

Paddlefish Polyodon spathula (30–67 cm total length, TL) were stocked in six flood control reservoirs (<41 ha) in western Kentucky in January 1995 at a target stocking density of 10 fish/ha. Fish growth was monitored quarterly beginning in July 1995. The fish were implanted intraperitoneally with passive integrated transponder (PIT) tags. Chemical and physical variables and zooplankton biomass were measured monthly. Three reservoirs that had not been stocked were sampled monthly as controls. Of the 1,440 paddlefish stocked, 353 were recovered at harvest in the fall of 1996, and only two tags were found. Anecdotal evidence indicated some loss to predation by largemouth bass Micropterus salmoides and some to escapes through mechanical spillways. The total gross yield was 1,715 kg or 13.7 kg/ha; it ranged from 0.6 to 28.8 kg/ha. Gill nets of 102-mm-bar mesh were optimum for harvest. Mean harvest weights were significantly different among reservoirs. A positive correlation was found between relative growth and mean total alkalinity measured during the April–October growth season. Relative growth was also positively correlated with mean sample site depth and conductivity measured during the growth season. The mean harvest weight was negatively correlated with photic zone depth. Paddlefish growth was lower in reservoirs infested with macrophytes during the growth season, and condition factors at harvest were significantly different among some reservoirs. Our results indicated that reservoir ranching is a viable method for producing market-size paddlefish within the limits set by reservoir fertility. We conclude that PIT tags are not suitable for paddlefish when implanted in the body cavity. There was no evidence that paddlefish grazing at the densities that were realized adversely affected existing reservoir ecosystems.