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Population Ecology of the Lake Erie Water Snake, Nerodia sipedon insularum

1986; American Society of Ichthyologists and Herpetologists; Volume: 1986; Issue: 3 Linguagem: Inglês

10.2307/1444959

1938-5110

Richard B. King,

Water Quality and Resources Studies

Population ecology of the Lake Erie water snake, Nerodia sipedon insularum, is described based on a 5 yr capture-mark-recapture study involving 1449 captures of 1247 individuals. Water snakes are widespread in the island area of Lake Erie but have declined in numbers and have disappeared from one island within the last 50 yr. Population estimates for adult snakes range from 25 to about 500 individuals on seven islands. Snakes are active from late April until early October. Males are caught most often during the breeding season in May and June, while females are taken more often later in summer. Females appear to feed over a longer portion of the active season than males, grow at a faster rate (0.014 vs 0.012 cm/d mean growth rate) and attain a larger body size (82.1 vs 62.5 cm mean snout-vent length). Weight gain occurs throughout the active season in adult females but is restricted to mid-summer in adult males. Some females reproduce annually but smaller females may skip opportunities to reproduce. Number and size of offspring are positively correlated with female size. Comparisons with data from mainland populations elsewhere in the range of this species indicate that island water snakes differ in having larger adult body sizes (mean snout-vent length is 10-16 cm greater in males and 13-14 cm greater in females), lower growth rates (maximum growth rate is 0.06 cm/d vs 0.13 cm/d in mainland populations) and shorter tails (by 2-5% in males, 1-3% in females). In addition, litter size is less strongly correlated with female body size in island populations (r2 = 0.17 vs 0.34-0.72 elsewhere). Differences may also exist in size of newborns (mean newborn SVL of mainland population ranges from 12% shorter to 4% longer than that of island populations), diet (mainland populations typically consume more amphibians and fewer fish) and intensity of predation (frequency of stub tails is two times greater in mainland populations).