Population response of triploid grass carp to declining levels of hydrilla in the Santee Cooper Reservoirs, South Carolina

摘要

Approximately 768,500 triploid grass carp (udCtenopharyngodonudidellaudValenciennes) were stocked into the Santee Cooperudreservoirs, South Carolina between 1989 and 1996 toudcontrol hydrilla (udHydrilla verticillataud(L.f.) Royle). Hydrillaudcoverage was reduced from a high of 17,272 ha during 1994udto a few ha by 1998. During 1997, 1998 and 1999, at least 98udtriploid grass carp were collected yearly for population monitoring.udEstimates of age, growth, and mortality, as well asudpopulation models, were used in the study to monitor triploidudgrass carp and predict population trends. Condition declinedudfrom that measured during a previous study in 1994.udThe annual mortality rate was estimated at 28% in 1997, 32%udin 1998 and 39% in 1999; however, only the 1999 mortalityudrate was significantly different. Few (2 out of 98) of the triploidudgrass carp collected during 1999 were older than age 9.udWe expect increased mortality due to an aging populationudand sparse hydrilla coverage. During 1999, we estimated aboutud63,000 triploid grass carp system wide and project less thanud3,000 fish by 2004, assuming no future stocking.ududmanagement, population sizeudCtenopharyngodon idella, Hydrilla