Field-Based Age Estimation of Juvenile Galapagos Sea Lions (Zalophus wollebaeki) Using Morphometric Measurements

Abstract: Information about the age of juvenile pinnipeds is necessary for an understanding of ontogeny-specific patterns and strategies. Exact age determination of juvenile cohorts from wild populations is best achieved through birth observations and sub-sequent marking, but this involves a considerable time lag during which juveniles mature. A combination of body and teeth measurements of known-age Galapagos sea lion juveniles taken during brief routine captures in the field was used to create age prediction models. Several general linear models (GLMs) produced reliable age estimates for male and female juveniles up to an age of 2 y. Teeth measurements were important predictors of age: male age was best estimated using upper canine length (CL), mass, and girth, while the best predictors for female age were CL, canine width (CW), body length (SL), body mass, and an interaction between CL and CW. The presented method of aging wild unmarked juveniles in the field is applicable during routine captures, requires little equipment, and yields a considerable increase of information for studies involving brief sampling periods in the field. We suggest its adjustment, testing, and application in studies of juveniles of other species.

Key Words: age estimation, field method, tooth measurements, general linear models, Galapagos sea lion, Zalophus wollebaeki

Document Type: Research article

DOI: 10.1578/AM.36.3.2010.262

Page Numbers: 262-269

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