POPULATION SIZE AND RECOVERY CRITERIA OF THE THREATENED LAKE ERIE WATERSNAKE: INTEGRATING MULTIPLE METHODS OF POPULATION ESTIMATION

Abstract

ABSTRACT The Lake Erie watersnake, Nerodia sipedon insularum, occurs only in the island region of western Lake Erie, an area less than 40 km in diameter. Restricted geographic distribution and declining population size resulted in this snake's classification as Threatened in the U.S. and Endangered in Ontario and Ohio. A combination of mark-recapture methods, capture rate information, and interpolation were used to estimate the current U.S. population size of Lake Erie watersnakes. A total of 121 point estimates were generated using both ‘closed’ population (Lincoln–Petersen, Schumacher's) and ‘open’ population (Jolly–Seber, Bailey's triple-catch) methods to analyze data collected from 1980–2004. Paired t-tests, comparing estimates obtained using alternative methods, were consistently non-significant. Although standard errors and confidence intervals of individual estimates were often large, standard errors of mean estimates, obtained by averaging across methods and sets of consecutive years, were markedl...