A field-based method for estimating age in free-ranging steller sea lions (Eumetopias jubatus) less than twenty-four months of age.

摘要

Studies of health, survival, and development of juvenile Alaskan Steller sea lions (Eumetopias jubatus, SSL) require accurate estimates of age for wild-captured animals. However, the value and accuracy of several potential predictors of age have not been assessed with data from known-age free-ranging animals. During 2001-2005, forty-six individual SSL originally branded or tagged at <=6 mo of age were recaptured by the Alaska Department of Fish and Game (ADF & G). Using a series of general linear models, we evaluated the ability of morphometrics measurements: permanent canine tooth length (CTL), diastema (DIAS), whisker length (WHIS), and dorsal standard length (DSL) to predict the age of forty-six known-age juveniles (n = 46 <=23 mo of age). Permanent CTL was the strongest individual predictor (r2 = 0.80); followed by DSL, DIAS, and WHIS (r2 = 0.70, 0.56, and 0.45, respectively). The inclusion of a single sample from a 44-mo-old sea lion suggested quadratic relationships between age and all predictors for older animals. Only models including CTL predicted age to within 6 mo of known age. The equation Age = (-3.0112 + (0.6726 * CTL) + (0.4965 * DIAS)) allows for accurate age estimates of SSL =23 mo for both sexes.