Refining aging criteria for northern sea otters in Washington State

Journal of Fish and Wildlife Management
By: , and 



Measurement of skull ossification patterns is a standard method for aging various mammalian species and has been used to age sea otters Enhydra lutris from Russia, California, and Alaska. Cementum annuli counts have also been verified as an accurate aging method for sea otters in Alaska. In this study, we compared cementum annuli count results and skull ossification patterns as methods for aging the northern sea otter, E. l. kenyoni, in Washington State. We found significant agreement between the two methods, suggesting that either method could be used to age sea otters in Washington. We found that ossification of the squamosal–jugal suture at the ventral glenoid fossa can be used to differentiate male subadults from adults. To assist field biologists or others without access to cementum annuli or skull ossification analysis techniques, we analyzed a suite of morphologic, physiologic, and developmental characteristics to assess whether a set of these more easily accessible parameters could also predict age class. We identified tooth condition score, evidence of reproductive activity in females, and tooth eruption pattern as the most useful criteria for classifying sea otters in Washington. We created a simple decision tree based on characteristics accessible in the field or at necropsy, which can be used to reliably predict age class of Washington sea otters as determined by cementum annuli. These techniques offer field biologists and marine mammal stranding networks a replicable, cost-conscious methodology to gather useful biological information from sea otters.

Study Area

Publication type Article
Publication Subtype Journal Article
Title Refining aging criteria for northern sea otters in Washington State
Series title Journal of Fish and Wildlife Management
DOI 10.3996/052017-JFWM-040
Volume 9
Issue 1
Year Published 2018
Language English
Publisher Scientific Journals
Contributing office(s) National Wildlife Health Center
Description 14 p.
First page 208
Last page 221
Country United States
State Washington
Google Analytic Metrics Metrics page
Additional publication details