Growth rates of vibrissae of harbor seals (Phoca vitulina) and Steller sealions (Eumetopias jubatus)

Growth rates of vibrissae (whiskers), which act as a temporal record of fee ding in harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jub atus), were estimated using C-13- and N-15-labeled glycine followed by stab le-isotope analysis. The labeled glycine was incorporated into keratin and served as a temporal marker for growth-rate calculation. One captive harbor seal received two doses 147 days apart, while a second seal received one d ose; vibrissae were analyzed after 86 and 154 days. The peak positions indi cated that growth began in the fall, continued into spring, but ceased in J une, with active growth rates of 0.33 mm/day. Two adult captive Steller sea lions each received two labeled doses during a 308-day period. After 427 d ays vibrissae in both sea lions showed two peaks corresponding to the marke rs; growth rates were calculated as 0.05-0.07 mm/day. Growth rates in capti ve juvenile and wild adult Steller sea lions, 0.10-0.17 mm/day, supported t he assumption that major isotopic oscillations in vibrissae of wild sea lio ns were annual. The multiyear records imply that Steller sea lions retain t heir vibrissae; harbor seal vibrissae, in contrast, have periods of rapid g rowth and appear to be shed, at least in part, annually.