The Impacts of Hurricane Katrina on a Population of Yellow-Blotched Sawbacks (Graptemys flavimaculata) in the Lower Pascagoula River
The Yellow-blotched Sawback (Graptemys flavimaculata) is a riverine turtle that is endemic to the Pascagoula River system of southern Mississippi, USA. Population declines led to Federal listing as a threatened species in 1991, with the most robust population inhabiting the Lower Pascagoula River near Vancleave, MS (approx. 24 river km from the Pascagoula River mouth). We conducted a mark-resight survey of this population during the spring and summer of 2005-2006. On 29 August 2005, Hurricane Katrina entered the Mississippi Gulf Coast, the location of our study site. On 13 October 2005, we conducted a one-hour preliminary visual survey by boat through the study area and we identified eight individuals that we marked prior to Katrina’s landfall. This demonstrated that at least some of the 49 previously-marked individuals remained in the study area. Later, we conducted more extensive mark-resight surveys within the same 3.5 km section of river in October of 2005-2006. The population estimate for 2006 was significantly lower than the 2005 population estimate for the same stretch of river, suggesting that numbers substantially decreased during the year following the hurricane. Of the plausible explanations for this pattern, the available evidence most strongly supports a real decline in population, presumably due to the long-term impact of Hurricane Katrina. Possible reasons for such a long term effect include hurricane induced saltwater intrusion and low levels of dissolved oxygen with direct impacts on individuals or indirect impacts on the prey populations (e.g., gastropods and other aquatic macroinvertebrates). Follow-up surveys are planned to investigate further these influences on the long-term population trends of G. flavimaculata.