Effects of Trapping and Weather on Body Weights of Feral Nutria in Maryland

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Abstract
Rates of change in body weight of nutria from Maryland are calculated based on changes in weight and are expressed as the changes in weight per unit weight per unit time. A model of nutria rate of change in body weight is fitted to the data and used to predict the weight gain patterns of male and female nutria. The rate data are compared among the factors of sex, trapping method (leg trapped vs. live trapped), season (where winter is defined as Dec-Feb. and summer as the rest of the year), and year (March 1975-Feb. 1976 vs. March 1976-Feb. 1977) in analysis of covariance with inverse body weight as the covariate. A regression was made of mean fractional rates, adjusted for the covariate inverse body weight, against mean seasonal temperature and mean seasonal snowfall. Rates of change in body weight were significantly greater in 1975-1976 than in 1976-1977 reflecting the severe winter of the latter year. Leg trapped nutria grew consistently slower than live trapped nutria, although the difference was not significant at P < 0.05. There was a significant interaction between sex and season. In the summer, females grew faster than males, although this may be due, in part, to pregnancy. The pattern was reversed in the winter. There were significant correlations between mean adjusted rates of growth and both mean seasonal temperature (r = 0.83) and mean seasonal snowfall (r = 0.80). These factors could reduce food availability and make greater demands on metabolic energy.

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