In the Gulf of Alaska, beyond the narrow continental shelf adjacent to southeast Alaska, annual migrations of many marine animals follow the changing seasons. Zooplankton feed on drifting phytoplankton as they float along with the northward-moving currents. These plankton represent lower forms of almost every marine animal group, some of them vertebrates. The most prominent are: foraminifers, radiolarians, arrowworms, pteropods, salps, copepods, euphausiids, larval crustaceans (crabs and shrimp), coelenterate medusae, ctenophores, and fish larvae and eggs. These zooplankton nourish many fish species inhabiting these waters. Availability of phytoplankton and predation by fish control the abundance of these zooplankters. In general, changes in zooplankton abundance closely follow the timing of phytoplankton blooms.

Numerous pelagic fish feed on zooplankton and smaller fish in these waters. Five species of Pacific salmon along with steelhead trout grow in size as they seasonally move northward and counterclockwise around the Gulf of Alaska. When sexually mature, they begin to migrate toward the coast.

Several species of shark (including the salmon shark), the pomfret, and a variety of less abundant forms enter this offshore habitat from the south during the warmer summer season. In warmer than average years albacore tuna may even venture as far north as this region's offshore waters.

Several species of cetaceans, particularly Dall and harbor porpoises and humpback, finback, and Pacific killer whales, are common in offshore waters of the region. Gray whales abound during migration. Other less important cetaceans include little piked whales, Baird, Stejneger, and Cuvier beaked whales, sperm whales, right whale dolphins; Pacific striped porpoises; Pacific blackfish; and sei, blue and Pacific right whales (LeResche and Hinman 1973). The northern fur seal also passes offshore during migration, and the elephant seal has been recorded at the southern end of the region.

More than 50 species of seabirds have been sighted in the coastal waters of the region. These include the endangered short-tailed albatross, black-footed albatross, northern fulmar, sooty and slender-billed shearwaters, fork-tailed and Leach's storm-petrels, phalaropes, jaegers, several species of gulls, black-legged and red-legged kittiwakes, terns, common and thick-billed murres, guillemots, several murrelets, several auklets, and horned and tufted puffins. Some of these species breed on adjacent shores, some are winter residents, and some are only passing migrants, but many of them feed in the oceanic environment of the region for a significant period (U.S. Department of the Interior 1972).

Beneath the upper sunlit oceanic waters lie the dark abyssal depths (Figure 131). Organisms inhabiting this deeper habitat are nourished by photosynthetic production that settles from upper waters and organic materials that drift in with the currents. In very deep waters, bottom-dwelling organisms scavenge for organic matter among bottom sediments and predators are almost entirely absent.

Man rarely has any contact with the creatures of this environment. Scientific investigations reveal that they resemble similar types in shallower waters, but have developed sophisticated sensory mechanisms for mobility and feeding in a perpetually dark environment.

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Some of the most productive aquatic environment in this region lies on and above the continental shelf. A rich variety of benthic coelenterates, sponges, polychaete worms, assorted molluscs, numerous crustaceans, and slowly moving echinoderms live on and within the organically rich bottom sediments overlying the shelf. Some of the more commonly recognized forms include king and tanner crabs, weathervane scallops, starfish, and sea urchins. Dungeness crabs are most abundant near shore.

In the waters above the shelf, shrimp and such demersal (bottom-dwelling) fish as sablefish (blackcod), Pacific Ocean perch, and several other species of rockfish, Pacific cod, and a variety of flatfish including halibut swim and feed. Pelagic (living in open water) fish, such as herring and a number of rockfish species, spend most of their lives near the surface. Migratory species, such as salmon and steelhead trout, pass through these waters on their way to spawning streams. During outmigration from freshwater streams to salt water, juveniles of these same species spend several weeks or months, depending on water temperatures, feeding in coastal waters before moving far offshore.

The neritic environment is the source of food for several marine mammals. Dall and harbor porpoises and humpback, finback, Pacific killer, and gray whales, particularly the latter during their migration to and from wintering grounds in Baja California to their summer habitat in the Arctic, depend on the continental shelf habitat. Harbor seals and Steller sea lions feed on invertebrates and fish from this zone—the former diving as deep as 200 feet (60 m) and the latter as deep as 330 feet (100 m). Even the northern fur seal occasionally comes nearshore to feed on herring. Sea otters, once hunted nearly to extinction, have been successfully reintroduced into productive habitats (Burris and McKnight 1973).

The neritic environment is important to birds, not only the pelagic oceanic birds that spend much of their time over the continental shelf, but also to birds from nesting colonies that derive essentially all their food from the fish and invertebrate animals of the neritic zone. Many of these nesting birds also spend the remainder of the year here.

The coastline of southeastern Alaska has not been adequately explored by ornithologists, and detailed information on birds is difficult to obtain because of the birds' behavior and the inaccessibility of the sites. Rookeries are often located on steep rocky headlands or small rocky islands and islets that provide refuge from mammalian predators yet easy ocean access for adult birds and their young. Some birds nest deep in burrows, and some are nocturnal.

Nine seabird colonies have been identified in the region—Yakutat Bay Islands, Glacier Bay Island, Timbered Island, St. Nicholas Point, Noyes Island, Forrester Island and adjacent islands, Hazy Islands, St. Lazaria Island, and Necker Islands. In addition, such noncolonial species as three species of jaegers and various petrels, shearwaters, and albatrosses are present (LeResche and Hinman 1973). The St. Lazaria, Hazy, and Forrester Islands rookeries are National Wildlife Refuges.

Such waterfowl as harlequin ducks; common and king eiders; oldsquaws; black, white-winged, and surf scoters; and red-breasted mergansers also winter along the coasts of the region, spending a major portion of their time in the neritic zone.

Important Animals of the Marine Community

The partly enclosed waters of the intricate fjords of this region provide a unique aquatic habitat (Figures 130 and 132). Such species as sablefish (blackcod) and Pacific Ocean perch inhabit the neritic environment as adults and use these fjords as rearing areas. Adult salmon, char, and trout may linger briefly in fjords prior to ascending spawning streams. Seaward migrating immatures of these same species pause in coastal waters while their body metabolism adjusts to salt water before they migrate into offshore waters.

Unique bathymetric features in some fjords may limit or preclude the growth of benthic fauna. Many fjords have a shallow mound or sill at their mouths which limits water circulation in the deep basin within the fjord. With restricted circulation, bottom waters in such basins may become depleted of oxygen during summer. Organisms which require high oxygen concentration—fish, for example—will avoid such areas and nonmobile benthic invertebrates may die. Where a productive salmon spawning stream enters such a fjord, these stressful conditions may be intensified by dead salmon carcasses that drift out of the stream and settle to the bottom of the fjord. As they decompose, they also use up the limited supply of oxygen in these noncirculating waters (Barr and Knull 1973).

Glaciers terminating at salt water may also make the water turbid. Although the reduced light penetration should limit productivity, an apparent anomaly often exists, and large numbers of harbor seals may concentrate in such areas for extended periods, suggesting that the areas are probably productive food sources. Concentrations of mew gulls, kittiwakes, murres, and other marine birds are also known to occur in such situations. John Vania of the Alaska Department of Fish and Game states that he has captured large numbers of shrimp and flounder at the base of the Taku Glacier in winter, and their presence should attract seals and marine birds. The mechanisms that lead to such instances of apparent high productivity are not understood. Other than strictly oceanic species, birds that are normally found in the neritic environment may also be found in protected fjords.