| Fish | Shearwaters | Murres | Puffins | Fulmars | Gulls |
|---|---|---|---|---|---|
| Anchovy | X | — | — | — | — |
| Sardines | X | — | — | — | — |
| Herring | X | X | X | X | X |
| Sprat | X | — | — | — | — |
| Pilchard | X | — | — | — | — |
| Capelin | — | X | X | — | X |
| Salmon | — | X | — | — | — |
| Mackerel | — | X | — | — | — |
| Pollock | — | X | — | X | — |
| Haddock | — | X | — | — | — |
| Cod | — | X | — | — | — |
The significance of bird predation on pelagic or demersal fish and shellfish (Fig. 5) depends on the feeding behavior of the birds and on the life history of the fish (e.g., distribution, abundance, growth, and adult size). Pursuit diving birds, such as murres and puffins, can consume fish at greater depths than can birds that feed near the surface, such as shearwaters, kittiwakes, fulmars, and gulls.
Fig. 5. Feeding behavior and relative importance of food of some groups of marine birds that occur in the eastern Bering Sea.
Aspects of the Life Histories of Fish Related to Predation by Marine Birds
Fish that are pelagic during part of their lives, such as salmon and herring, and forage fish like smelt, capelin, and sand lance, are vulnerable to greater predation by a wider variety of marine birds than are bottom-dwelling demersal fish, such as pollock, cod, sole, ocean perch, and halibut, as well as king and snow crabs. Some species that live on the bottom as adults have pelagic stages during which they are vulnerable to predation by marine birds. Juveniles of some demersal species (pollock, cod, halibut, some species of sole, and king crabs) are sometimes found in shallow water where they might be subject to predation by birds.
Demersal Fish and Shellfish
The early life histories of the commercially important demersal fish of the eastern Bering Sea are quite different (Table 3). For example, the eggs and larvae of Pacific halibut (Hippoglossus stenolepis) generally occur at depths greater than 100 m (Hart 1973), whereas those of pollock and yellowfin sole are found at or near the surface (Musienko 1963, 1970). The eggs of Pacific cod are demersal, but the larvae are oceanic (pelagic) and occur from 25-150 m (Mukhacheva and Zviagina 1960).
In their juvenile stages, many demersal fish frequent the near-surface waters (Table 3), where they become vulnerable to predation by piscivorous marine birds. Juvenile pollock, for example, form into small schools that usually move about close to the bottom but sometimes move into areas as shallow as 3 m. Juvenile Pacific cod prefer the warmer water close to shore and may be found within 10 m of the surface (Moiseev 1953). The young of many species of flatfish, such as yellowfin sole, rock sole (Lepidopsetta bilineata), and flathead sole (Hippoglosoides elassodon), remain for a time in shallow warm water after assuming a demersal existence. Yellowfin sole 2-2.5 cm in total length may be found in abundance in areas as shallow as 5 m (Fadeev 1965; Moiseev 1953).