In order to clear any doubts regarding the comparative growth rates of the whiskers of harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus), researchers at the Institute of Marine Science, University of Alaska Fairbanks, and the Mystic Aquarium, CT, U.S.A. performed a series of experiments in 2001. The whiskers of participant seals and sea lions were stable-isotope-labeled with Carbon 13 and Nitrogen 15, and whisker growth rates were measured over a period of more than two years.
Seals: The peak positions indicated that growth began in the fall, continued into spring, but ceased in June, with active growth rates of 0.33 mm/day.
Sea Lions : After 427 days vibrissae in both sea lions showed two peaks corresponding to the markers; growth rates were calculated as 0.05 to 0.07 mm/day.
And further: “A harbor seal’s vibrissae (~10 cm) tend to be similar in length, while a Steller sea lion’s anterior mystacial vibrissae are short (~6 cm) and the posterior vibrissae much longer (>20 cm)”
Growth rates of vibrissae of harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus) was published in the Canadian Journal of Zoology, 2001, 79:(6) 1053-1061, and can be read in full here: