The harbor seal is probably the most widely known seal and is also referred to as the common seal. When hauled out on rocks or ledges, they often assume an arched position with their head raised and their hind flippers elevated, giving them the nickname "banana seal." These seals are widely distributed in the North Atlantic and North Pacific regions. Harbor seals are rather small seals with a big head, short body, and short limbs. Adults, on average, weigh 90-140 kg (190-309 lb) for males and 65-80 kg (143-176 lb) for females, though pregnant females may weigh up to 140 kg (309 lb). The average length for an adult harbor seal is 1.5-1.8 m (approximately 5-6 ft). Harbor seals come in two basic color patterns. Some are white or light gray to silver with dark spots, while others are black or dark gray to brown with white rings.

Harbor seals were thought to be the least vocal of the pinnipeds. Recent studies have shown, however, that males produce underwater vocalizations during the mating season to attract females or to compete with other males. Males establish territories in the waters offshore of haul-out sites. Using underwater vocalizations, they defend their territories against other males and display to females traveling through the area. Their underwater vocalization is described as a roar with a peak frequency at approximately 1.2 kHz. Harbor seals also produce a wide variety of in-air vocalizations, including short barks, tonal honks, grunts, growls, roars, moans, and pup contact calls.

References
• Hayes, S.A., Costa, D.P., Harvey, J.T. and Le Boeuf, B.J. 2004. Aquatic mating strategies of the male Pacific harbor seal (Phoca vitualina richardsi): Are males defending the hotspot? Marine Mammal Science 20(3): 639-656.
• Reeves, R.R., Stewart, B.S. and Leatherwood, S. 1992. The Sierra Club Handbook of Seals and Sirenians. San Francisco, CA: Sierra Club Books.
• Richardson, W.J., Green, C.R. Jr., Malme, C.I. and Thomson, D.H. 1995. Marine Mammals and Noise. San Diego, CA: Academic Press.
• Van Parijs, S.M. and Kovacs, K.M. 2002. In-air and underwater vocalizations of eastern Canadian harbour seals, Phoca vitulina. Canadian Journal of Zoology 80: 1173-1179.

Additional Resources
• Bjorgesaeter, A., Ugland, K.I. and Bjorge, A. 2004. Geographic variation and acoustic structure of the underwater vocalization of harbor seal (Phoca vitulina) in Norway, Sweden and Scotland. Journal of the Acoustical Society of America 116(4): 2459-2468.
• Hayes, S. A., Kumar, A., Costa, D. P., Mellinger, D. K., Harvey, J. T., Southall, B. L. and Le Boeuf, B. J. 2004. Evaluating the function of the male harbour seal, Phoca vitulina, roar through playback experiments. Animal Behaviour 67(6): 1133-1139.
• Van Parijs, S. M., Corkeron, P. J., Harvey, J., Hayes, S. A., Mellinger, D. K., Rouget, P. A., Thompson, P. M., Wahlberg and M., Kovacs, K. M. 2003. Patterns in the vocalizations of male harbor seals. Journal of the Acoustical Society of America 113(6): 3403-3410.
• Department of Ecology, Puget Sound Shorelines: Harbor Seal
• National Marine Mammal Laboratory: Alaska Harbor Seals
• The Marine Mammal Center: Harbor Seal