THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 



53 



otter populations, problems yet unsolved in keeping a captive 

 colony, and the fact that a regular annual harvest of wild animals 

 has not been taken, have prevented the accumulation of known- 

 age specimens. 



Lacking such basic material, but drawing on his experience in 

 the study of teeth for indications of growth layers and age esti- 

 mation, V. B. Scheffer studied a number of sea otter teeth from 

 young and old animals. Techniques that reveal growth layers in 

 teeth of other mammals revealed nothing that could be related to 

 the annual growth cycle in the sea otter. 



Dr. A. F. Forziati and Mrs. M. P. Kumpula, Research Division 

 of the American Dental Association, National Bureau of Stand- 

 ards, Washington, D.C., undertook a study of sea otter teeth. 

 Teeth were sectioned and subjected to techniques such as X-ray 

 photography and exposure to ultraviolet radiation. These and 

 other techniques useful in revealing growth layers in other mam- 

 malian teeth showed faint lines (fig. 28) but gave no useful in- 

 dication of annual growth layers. 



In a further effort to **mark" stages of tooth growth, three 

 captive sea otters on Amchitka Island were injected periodically 

 during a 3-month period with alizarin red S dye. It was hoped that 

 visible growth lines would be formed. When the teeth of these 

 animals were studied by Dr. Forziati and Mrs. Kumpula, how- 

 ever, no consistent markings were revealed. Further studies of 

 structures that may indicate age in the sea otter are reserved 

 for the future. 



Karl Schneider, Alaska Department of Game (letter, Nov. 1968), 

 tells me that he experimented with a number of different stains 

 and techniques and is now able to differentiate cementum layers 

 which appear to indicate age. 



The sea otter is a permanent resident in a relatively uniform 

 environment. It requires a daily food intake of uniform amount 

 (a captive consumed 15 lb. [6.8 kg.] of food per day during all 

 seasons). There is no abrupt molt or distinct period of fasting. 

 In the absence of marked seasonal environmental changes or 

 periodic metabolic changes during the sea otter's life, it is not 

 surprising that the usual indicators of chronological age are not 

 evident. 



One captive otter (Susie) was about 1 year old when captured 

 and died of abnormal causes after 6 years in captivity. Her teeth 

 and bone structure at death appeared to be those of a young adult. 

 On this basis it is estimated that in ideal habitat a wild sea otter 

 might be expected to live for from 15 to 20 years. A captive river 



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