Growth and age of Alberta long-toed salamanders (Ambystoma macrodactylum krausei): a comparison of two methods of estimation

Both skeletochronology and a somatic growth model based upon mark–recapture data were used to estimate life-span and the relationship between size and age in two populations of long-toed salamanders (Ambystoma macrodactylum krausei) in the upper Bow Valley of southwestern Alberta. Skeletochronologically aged salamanders (n = 170) displayed a sigmoidal relationship between snout–vent length and age, with a great deal of variation in snout–vent length within each year class. The modified logistic-by-mass somatic growth model (based upon 47 recaptures) predicted sexual maturity at 3 years of age and adult size at 6 years, with asymptotic length approached at 15 years of age. These predictions were falsified by skeletochronology, which indicated that a snout–vent length characteristic of sexual maturity could be reached by 2 years and adult size by 3 years of age, and that the maximum life-span attained was 10 years, with most individuals living 6 years at most. Considerable variation in growth, evidently due to factors other than simple age, is displayed among individuals in these populations. Their demographic characteristics suggest that the skeletochronologically determined maximum age is real and not due to a cessation of growth, and thus of bone deposition, in these salamanders.