| Fecundity | Spawning season | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Length of female (cm)[54] | Mean no. of eggs | Total period | Peak period | Life stage | Total length (cm)[56] | Depth from surface (m) | Seasonal period of pelagic life | Duration of life stages (days) | Source of data |
| Walleye pollock (Theragra chalcogramma Pallas) | |||||||||
| 31-35 | 95,700 | Feb.- June | April-May | Egg | 0.1-0.2 | 0-10 | Feb.-June | 12 at 6-7°C | Yusa 1954; Tanino et al. 1959; Kobayashi 1963; Musienko 1963, 1970; Serobaba 1968; Hart 1973[55] |
| 20.5 at 3.4°C[57] | |||||||||
| Larval | 0.4-0.9 | 10-25 | March-? | > 25 at 6-7°C | |||||
| 46-50 | 324,400 | — | — | Larval | 0.9-? | 25-? | ?-Sept. | ? | |
| — | — | — | — | Juvenile | 2.2-4.1 | 0-?[58] | Summer | — | |
| — | — | — | — | Juvenile | 6.0-30.0 | 4-37 | Summer | — | |
| — | — | — | — | Adult | 30.0-70.0 | 0-386 | — | — | |
| Pacific cod (Gadus macrocephalus Tilesius) | Egg | 0.1-0.11 | 100-250 | Demersal | 8-9 at 11°C | Moiseev 1953; Mukhacheva and Zviagina 1960; Musienko 1970; Hart 1973[55] | |||
| 60 | 1,200,000 | Jan.-March | ? | 17 at 5°C | |||||
| 28 at 2°C | |||||||||
| Larval | 0.5-3.2 | 25-150 | Feb.-Aug. | ? | |||||
| 78 | 3,300,000 | — | — | Juvenile | ? | 10-? | Summer | — | |
| — | — | — | — | Adult | 40.0-99.0 | 0-900 | — | — | |
| Pacific herring (Clupea harengus pallasi Valenciennes) | Egg | 0.1-0.2 | 0-12 | Demersal | 10-20[57] | Stevenson 1962; Musienko 1970; Rumyantsev and Darda 1970; Reid 1972; Hart 1973[55] | |||
| 20.5-22.0 | 26,600 | May-June | Varies | Larval | 0.9 | 0.5-8 | May-June | 42-56 | |
| 28.0-31.0 | 77,800 | — | — | Larval | 1.3 | 0.5-8 | June-July | ||
| — | — | — | — | Larval | 2.5 | 1-6 | July-Aug. | ||
| — | — | — | — | Juvenile | 2.5-20.5 | 0-? | March-Nov. | — | |
| — | — | — | — | Adult | 20.5-31.0 | 0-140 | March-Nov. | — | |
| Capelin (Mallotus villosus (Muller)) | Egg | 0.1 | <20 | Demersal | 14-? | Clemens and Wilby 1961; Musienko 1970; Hart 1973 | |||
| ? | 3,000 | June-July | ? | Larval | 0.5-? | ? | June-? | ? | |
| ? | 6,000 | — | — | Juvenile | ? | ? | March-Nov.(est.) | — | |
| 10.3 | 6,670 | — | — | ||||||
| ? | 60,000 | — | — | Adult | ? | 0-? | March-Nov. | — | |
| Pacific sand lance (Ammodytes hexapterus Pallas) | |||||||||
| — | ? | June- Aug. | [59] | Egg | ? | ? | Demersal | ? | Musienko 1963, 1970; Kashkina 1970; Hart 1973 |
| — | — | — | — | Larval | 0.7-3.4 | 0-? | June-Sept. | ? | |
| — | — | — | — | Juvenile | 3.6-9.6 | 0-? | ? | — | |
| — | — | — | — | Adult | 26 | 0-? | ? | — | |
| Pacific ocean perch (Sebastes alutus (Gilbert)) | |||||||||
| 26 | 10,000 | March-May | ? | Egg[61] | — | — | — | — | Paraketsov 1963; Lisovenko 1965; Lyubimova 1965; Kashkina 1970[60] |
| 44 | 180,000 | — | — | Larval[62] | 0.6-? | [62] | March-Aug. | ? | |
| — | — | — | — | Juvenile | 6.2 | 37-128 | — | — | |
| — | — | — | — | Juvenile | 10.4 | 37-154 | — | — | |
| — | — | — | — | Juvenile | 14.7-21.3 | 37-230 | — | — | |
| — | — | — | — | Adult | 21.3-51.0 | 37-420 | — | — | |
| Pacific halibut (Hippoglossus stenolepis Schmidt) | |||||||||
| 75 | 101,723 | Oct.-March | ? | Egg | 0.3-0.4 | 40-935 | Oct.-March | 48 at ? | Novikov 1964; Hart 1973 |
| 135 | 2,800,837 | — | — | Larval | 0.8-1.5 | >200 | Nov.-May | 70-98 | |
| — | — | — | — | Larval | 1.5-2.9 | <100 | May-Sept. | ||
| — | — | — | — | Juvenile | 3.4-4.2 | 7-43 | — | — | |
| — | — | — | — | Juvenile | 19-25 | 7-45 | — | — | |
| Yellowfin sole (Limanda aspera (Pallas)) | |||||||||
| 26.1-28.0 | 1,295,000 | June-Aug. | July | Egg | 0.07-0.09 | >0 | June-Aug. | 9.4 at 13.1°C[57] | Moiseev 1953; Pertseva-Ostraumova 1954; Musienko 1963; Fadeev 1965; Kashkina 1965a, 1965b[55] |
| 40.1-42.0 | 3,319,500 | — | — | Larval | 0.2-1.2 | >0 | July-Oct. | ? | |
| — | — | — | — | Juvenile | 2.1-2.5 | 5-15 | — | — | |
| King crabs (Paralithodes camtschatica (Tilesius)) | |||||||||
| 9.4 | 55,408 | April-June | ? | Egg | — | 100-200[63] | — | ? | Kurata 1960, 1964; Korolev 1964; Rodin 1970 |
| 17.1 | 444,651 | — | — | Zoeal | 0.55-0.65 | ? | April-July | 33 at 7-10°C | |
| — | — | — | — | Zoeal | 23 at 12.3-12.5°C | ||||
| — | — | — | — | Glaucothoeal | 0.38x0.18 | ? | May-? | ? | |
| — | — | — | — | Juvenile | ? | 1-? | — | ? | |
| Snow crabs (Chionoecetes bairdi Rathbun) | |||||||||
| ? | ? | ?[65] | ? | Egg | — | 100[63] | — | ? | Haynes 1973[55] Jewett and Haight[64] |
| — | — | — | — | Prezoeal | 0.22-0.28 | ? | May-? | 1-2 at 2.5°C | |
| — | — | — | — | 1st zoeal | 0.50-0.56 | ? | Summer | ? | |
| — | — | — | — | 2d zoeal | ? | 0-10 | Summer | ? | |
| — | — | — | — | Megalopal | 0.30-0.35x | ? | Summer | — | |
| 0.18-0.21 | |||||||||
| — | — | — | — | Juvenile | 0.44-0.48x | ? | — | — | |
| 0.32-0.35 | |||||||||
| Snow crabs (Chionoecetesopilio (O. Fabricius)) | Egg | ? | 93[60] | — | ? | Ito 1968; Kon 1970; Haynes 1973; Motoh 1973; Jewett and Haight[64] | |||
| ? | ? | ?[65] | ? | Prezoeal | — | ? | May-? | 63-66 at 11-13°C | |
| — | — | — | — | 1st zoeal | 0.48-0.54 | ? | Summer | ||
| — | — | — | — | 2d zoeal | 0.62-0.71 | ? | Summer | ||
| — | — | — | — | Megalopal | 0.29-0.33 | ? | Summer | ||
| — | — | — | — | 0.19 | |||||
| — | — | — | — | Juvenile | 4.4-4.8x | ? | — | — | |
| — | — | — | — | 3.2-3.5 | |||||
The commercially important king and snow crabs of the eastern Bering Sea also have larval stages that are pelagic (Table 3). Zoeae and megalopa of snow crabs are found near the surface where they are vulnerable to plankton-feeding marine birds. The eggs of king crabs are attached to the abdomen of the female, but after hatching, the larvae become pelagic and occur near the surface. They are planktonic through five larval stages before settling to the bottom to take up demersal residence (Kurata 1960, 1964). These larvae attain a length of 5.5-6.5 mm and spend 33 days or more in the plankton (Kurata 1960). Even after the young king crabs have settled to the bottom, they may still frequent water shallow enough to make them vulnerable to predation by some marine birds. Juvenile king crabs 1 and 2 years of age appear to prefer shallower water than do older crabs. In southeastern Alaska, during the spring, small juvenile crabs have been observed in pods at depths as little as 1 m below the low tide level.
The available life stages of king and snow crabs and commercially important demersal fish (Table 3) represent an enormous food supply for other fishes and marine birds. Predation by marine birds on pelagic eggs and on the larval and juvenile stages of demersal fish is not well documented, probably because the rapid digestion rate of birds makes species identification of these stages difficult. Investigators must often depend on the presence of the hard parts of fish (such as scales and otoliths) in the stomachs of birds to identify the species eaten. Because these hard parts have not yet formed in the larvae and most juveniles, predation by marine birds on older fish is more apparent on examination of stomach contents. Full understanding of predation by marine birds on demersal fish and shellfish requires additional data on when and where the egg, larval, and juvenile stages are present.
Pelagic Fish
Many fish, such as herring, capelin, smelt, and salmon, are pelagic for part of their lives, particularly during the spring and summer feeding periods. The extent of predation by marine birds on these species depends primarily on the location of their spawning grounds, their growth rates, and the size of the adults. The spawning location determines the extent of predation on eggs, whereas growth rate and adult size determine during how much of its lifetime a given fish species is vulnerable to the wide variety of marine birds.
Herring spawn in intertidal and subtidal zones and spend most of their post-larval lives in bays or estuaries near the coast. They deposit their adhesive eggs primarily on vegetation, and the eggs are particularly vulnerable to predation by a wide variety of marine and terrestrial birds. Outram (1958) estimated that gulls alone accounted for 39% of the egg loss on the spawning grounds at Vancouver Island, British Columbia. When herring larvae hatch, they are between 0.7 and 0.8 cm long; when they metamorphose about 6-8 weeks later, they are between 2.6 and 3.5 cm long. Thereafter, juvenile herring grow rapidly and reach a length of about 7-10 cm before winter. Although herring as old as 13 years and up to 38 cm long have been reported in Alaska, they seldom exceed 30 cm and 11 years of age (Rounsefell 1929). During spring and summer, herring are commonly within 10 m of the surface, but in winter, they are in water 100-140 m deep. Although herring are particularly vulnerable to predation in spring and summer, they are available to marine birds during most of their life.
The life history of capelin is somewhat different than that of herring—they live in the open sea near the surface and throughout the water column most of their lives. Sometime in June or early July, they migrate in large schools toward shore to spawn (Musienko 1970). In British Columbia, capelin bury their eggs in coarse sand and gravel in the intertidal and subtidal zones. The larvae are 0.5-0.7 cm long at hatching and are carried by currents to the open sea where they develop in the plankton. Capelin attain an age of 5 years and a maximum length of about 22 cm; their small size makes them vulnerable to predation by marine birds most of their lives, and they are an important pelagic food fish for other commercial fish in the Bering Sea.
The sand lance reaches a maximum size of 20-26 cm and is vulnerable to bird predation during most of its life. Little information is available on the maximum age attained by this species in the Bering Sea, but because of its size, it is an important forage fish for many commercial fish species.
The five species of Pacific salmon of the eastern Bering Sea spawn in fresh water, unlike herring, capelin, and sand lance. Their eggs are not vulnerable to extensive predation by marine birds; gulls take mainly salmon eggs which have been dislodged from the gravel and are drifting or being rolled along the stream bottom by the current (Moyle 1966). After a few months to several years in fresh water, the juvenile salmon (5-14 cm long) enter the Bering Sea during late spring or early summer and migrate through these waters to feeding grounds, primarily in the north Pacific Ocean. At maturity, the survivors return to their home streams and rivers to spawn. It is during the seaward migratory phase of their life cycle that salmon are most vulnerable to predation by marine birds.