A FIELD-BASED METHOD FOR ESTIMATING AGE IN FREE-RANGING STELLER SEA LIONS (EUMETOPIAS JUBATUS) LESS THAN TWENTY-FOUR MONTHS OF AGE

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 ( r ²= 0.80); followed by DSL, DIAS, and WHIS ( r ²= 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.