Harbor seals are mainly found in the coastal waters of the continental shelf and slope, and can be found commonly in bays, rivers, estuaries, and intertidal areas. On land, harbor seals are extremely wary and shy, and it is almost impossible to approach them when they are ashore without stampeding them into the water.  In contrast, while in the water, these essentially non-migratory seals can be curious, often craning their necks to peer at people on shore or in boats. Most harbor seal haul-out sites are used daily, based on tidal cycles, although foraging trips can last for several days.

Harbor seals are gregarious at haul-out sites, however they usually do not lie in contact with each other. A hissing rolling growl is one of the few vocalizations made by this seal, and it frequently accompanies foreflipper slapping, batting and scratching of neighboring seals.  This is a common occurrence at crowded haul-outs where animals moving and shifting positions bump into or move to close to one another.  At sea, they are most often seen alone, but occasionally occur in small groups.  Localized aggregations can form in response to feeding opportunities and concentration of prey. 

The mating system is promiscuous or weakly polygynous.  Mating usually takes place in the water, during the February to October breeding season.  Pupping peaks sometime between April and July.  In some regions, pupping occurs earlier in more southerly areas. 

Harbor seals are generalist feeders taking a wide variety of fish, cephalopods, and crustaceans obtained from surface, mid-water, and benthic habitats. Although primarily coastal, dives to over 500 m have been recorded.

Many harbor seals live in close proximity to large populations of humans and are exposed to high levels of industrial and agricultural pollutants.  Both chronic oil spills and discharges, and episodic large scale spills cause direct mortality, and have long term impacts on harbor seal health and their environment.

Harbor seals live in coastal areas in the middle of some of the most heavily fished waters on earth, and as a result there are entanglement issues as well as effects on the food chains they depend on for their prey.  There are also conflicts with smaller localized fisheries, and historically there have been organized population reduction programs and bounties for taking seals.

Mass die-offs from viral outbreaks have claimed thousands of harbor seals.  In the late 1980s more than 18,000 harbor seals are estimated to have been killed by a phocine distemper virus (morbillivirus).  Exposure to diseases from proximity to human populations, and the concentrations of pets and scavenging animals that live with and near them create an increased risk of exposure to communicable diseases.  Immunosuppression from chronic exposure to pollutant contaminants probably contributes to harbor seal susceptibility to diseases.

Despite the fact than most harbor seals live in relatively close proximity to humans, their population levels are generally not well know.  Combining recent estimates yields a world-wide population of 300,000 to 500,000 animals.  P. v. stejnegri  of the western Pacific (approximately 7,000), and P. v. mellonae (120-600), of the seal lakes of the Ungava Peninsula, Canada, may be the subspecies most at risk due to low population numbers.  Populations in Svalbard and the Baltic Sea, both in the hundreds, are also dangerously low.

For current information on the conservation status of this species, please consult the following websites: 

• IUCN Species Redlist    
• CITES webpage
• NMFS Stock Assessment Reports

BIGG, M. A. 1981.  Harbour seal-Phoca vitulina Linnaeus, 1758 and P. largha Pallas, 1811.  Pp. 1-27 in S. H. Ridgway and R. Harrison, eds. Handbook of marine mammals, Vol. 2: Seals.  Academic Press.

BOWEN, W. D., AND G. D. HARRISON.  1996. Comparison of harbour seal diets in two inshore habitats of Atlantic Canada.  Canadian Journal of Zoology 74:125-135.

BURNS, J. J.  2002.  Harbor Seal and Spotted Seal Phoca vitulina and P. largha..  Pp. 552-560 in W. F. Perrin, B. Wursig, and J. G. M.  Thiewissen, eds.  Encyclopedia of Marine Mammals. Academic Press.

KING, J. E.  1983.  Seals of the world.  Second Edition.  British Museum (Natural History), Comstock Publishing Associates, and Cornell University Press.  240 pp.

TEMTE, J. L.  1994. Photoperiod control of birth timing in harbour seal (Phoca vitulina).  Journal of Zoology, London 233:369-384.