V. D. Marine Mammals |
A number of marine mammals are found in Puget Sound waters, including Harbor Seals (Phoca vitulina), California sea lion (Zalophus Californianus), Steller (Northern) sea lion (Eumetopias jubatus), harbor porpoise (Phocoena phocoena), killer whale (Orcinus orca) and the gray whale (Eschrichtius robustus). Although some populations are considered stable and have grown recently, such as harbor seals, others have declined in recent years, partially due to human impacts such as high concentrations of contaminants found in food supplies, and incidental deaths due to commercial fishing operations (Calambokidis and Baird 1994; Puget Sound Water Quality Action Team 2002).
Harbor seals (Phoca vitulina) are the most abundant marine mammal in the Puget Sound region (Harley 1998) (Figure V-9). Washington’s harbor seal populations are considered abundant and healthy, numbering in excess of 30,000 seals (inland stocks +14,000 seals) (Jeffries et al. 2001). They are considered nonmigratory, are opportunistic foragers and feed on a wide variety of fish species, and to a lesser degree on cephalapods and crustaceans (Calambokidis and Baird 1994). The diet of harbor seals in Hood Canal was determined during the fall and spring of 1998 and 1999 from haulout sites at Quilcene Bay, Dosewallips River, Duckabush River, Hamma Hamma River and Skokomish River. Based on frequency of occurrence, Pacific hake, Pacific herring, and salmon (variety of species) were the most predominant food items found in the fall. Northern anchovy and three-spine stickleback were additional prey species identified during the spring (Lance et al. 2001). During the fall of 1998-2000, WDFW and Washington Cooperative Fish and Wildlife Research Unit began efforts to evaluate potentially negative effects of predation by harbor seals on the recovery of summer chum salmon runs in Hood Canal. Results indicated documented harbor seal predation on returning adult salmon off the mouths of the Quilcene, Dosewallips, Duckabush, and Hamma Hamma River systems. Seals were observed consuming summer chum, coho, and fall chum all three years (London et al. 2001).
Figure V-9. Harbor seal (Phoca vitulina) (Source: www. dnr.metrokc.gov/wlr/waterres/ marine/img/).
Harbor seals are the only pinniped that breeds in Puget Sound waters. Pups are born in eastern bays of Puget Sound between late June and August, and between mid-July and September in Southern Puget Sound. Harbor seals can potentially use any beach in Puget Sound as a haulout site for pupping; however, documented haulout sites known as rookeries are commonly used. Aerial, boat, and ground surveys conducted since 1978 indicate more than 200 haulout sites in the Strait of Juan de Fuca, San Juan Islands, Puget Sound and Hood Canal. Near Bainbridge Island, haulout sites have been noted at Blakely Rocks and Orchard Rocks (Jones and Stokes Associates 1990).
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