Project title: Freshwater sport fish management and enhancement - Threadfin shad prey production in tropical reservoirs (IHB)

Results description: Our team FishEcU (Institute of Hydrobiology, BC AS CR, v.v.i.) had a three-year subcontract (2009-2011) within a five-year project of the Mississippi State University (applicants: J.W. Neal, R. Kroger, C.G. Lilyestrom, financial support: Puerto Rico department of Natural and Environmental Resource). The aim of the subcontract was to describe populations of prey species threadfin shad Dorosoma petenense in reservoirs of Puerto Rico. Threadfin shad is small and short-lived species from family of clupeids, which feed on plankton. In Puerto Rico, threadfin shad is principally the only prey species for large-mouth bass Micropterus salmoides, which is the most desired species of sport fishing in USA and Puerto Rico as well. It has been showed that, contrary to predictions, bass do not grow to trophy sizes in Puerto Rican reservoirs. Possible explanation is lack of prey, i.e. low abundance of threadfin shad. Within the subcontract, we selected the best gear (gillnets or trawl) for sampling shad firstly. We found out that the assessment of shad abundance in conditions of tropical reservoirs of Puerto Rico can be best derived from trawl catches. Threadfin shad abundance varied through the year due to high densities of freshly hatched shad that were most numerous in winter and spring catches. Further, spatial pattern of shad distribution was studied, which was important for description of ecology of this species as well as for proper sampling gear. Threadfin shad preferred upper parts of the water column down to 3 m of depth and their catches were higher in the open water in comparison to inshore habitats. Abundance of threadfin shad was related to trophy of a reservoir being higher with higher concentration of nutrients.