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A FIELD‐BASED METHOD FOR ESTIMATING AGE IN FREE‐RANGING STELLER SEA LIONS ( EUMETOPIAS JUBATUS ) LESS THAN TWENTY‐FOUR MONTHS OF AGE
Author(s) -
King James C.,
Gelatt Thomas S.,
Pitcher Kenneth W.,
Pendleton Grey W.
Publication year - 2007
Publication title -
marine mammal science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.723
H-Index - 78
eISSN - 1748-7692
pISSN - 0824-0469
DOI - 10.1111/j.1748-7692.2007.00108.x
Subject(s) - morphometrics , juvenile , biology , zoology , age groups , fishery , demography , ecology , sociology
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.