Tooth emergence data for Enhydra lutris nereis (in days) at Monterey Bay Aquarium collected between 2004 and 2011 that were used to differentiate pup and juvenile age classes in an investigation to refine aging criteria and methods for sea otters in Washington. If deciduous canine teeth were present or permanent canine teeth were first erupting, the individual was classified as a pup. The animal was classified as a juvenile when the permanent canine teeth were partially to fully erupted. Deciduous (lower case) and permanent (upper case) teeth were scored as follows: incisors (i/I), canines (c/C), premolars (p/P), and molars (M). Tooth number corresponds to position in either the left or right dental arcade relative to the front or center, a superscripted number denotes a tooth in the maxilla, and a subscripted number denotes a tooth in the mandible. Deciduous maxillary and mandibular central incisors (i1and i2) were not included in the data because these teeth often do not emerge through the gingival surface before replacement by permanent incisors. Teeth were considered first erupting when any portion of the tooth crown was visible through the gingival surface and were considered fully erupted when >75% of the tooth was visible. *Teeth present at the time of birth. **Teeth for which emergence could not be distinguished from full eruption due to the small size.