Harbor seals prefer to frequent familiar resting sites. They may spend several days at sea and travel up to 50 km in search of feeding grounds, and will also swim 100+ miles upstream into fresh water in large rivers.  Resting sites may be both rugged, rocky coasts, such as those of the Hebrides or the shorelines of New England, or sandy beaches. Harbor seals frequently congregate in harbors, bays, sandy intertidal zones, and estuaries in pursuit of prey fish such as salmon, menhaden, anchovy, sea bass, herring, mackerel, cod, whiting and flatfish, and occasionally shrimp, crabs, mollusks, and squid. Atlantic subspecies of either Europe or North America also exploit deeper-dwelling fish of the genus Ammodytes as a food source and Pacific subspecies have been recorded occasionally consuming fish of the genus Oncorhynchus. Although primarily coastal, dives to over 500 m have been recorded. Harbor seals have been recorded to attack, kill and eat several kinds of duck.