Herrings And Sardines

The herrings are commercially important in that they support a variety of food fish markets (Fig. 4). Until the late 1960s, the herring was reduced and utilized heavily as a source of oil and fish meal. The herring has and continues to be used for pet food. Herring as food for humans has had a long history. Today, they are sold fresh, frozen, smoked (kippers), and pickled. The smaller Atlantic herring, which are canned, is well known around the world as a sardine. The larger Atlantic herring are canned as kipper snacks and fillets. The roe from herring has recently found a market in Japan as a delicacy item known as kazunoko, as their local herring populations have declined. The herrings belong to the family Clupeidae. Both Atlantic and Pacific herrings are subspecies of the species Clupea harengus. The two fish look similar, characterized by a silvery body

Figure 4. Herring (Clupea harengus harengus). Source: Copyright 1990 by B. Guild-Gillespie.

Figure 4. Herring (Clupea harengus harengus). Source: Copyright 1990 by B. Guild-Gillespie.

Plant Derived Amylases

that is highly compressed laterally, large cycloid scales and large eyes. The pearl essence from the scales was in high demand during the 1940s for use in high-quality paints for aircrafts.

The Pacific sardine (Sardinops sagax) is commonly referred to as the pilchard. It is not the fish that North Americans commonly refer to as the sardine. While the pilchard has some commercial value for its oil and for fish meal, very little is canned.

Pacific Herring

The Pacific herring is fished today for its roe and for reduction purposes. Both herring and herring spawn have been fished by the North American natives since 800 bc. The commercial herring fishery that began in the late 1800s was based on the salted herring market. This was replaced by a fishery based on the reduction industry in which the herring carcasses were reduced for oil and meal for commercial feeds for poultry and fish culture. The relatively new market of herring roe for the Japanese market started in the early 1970s. Today, the herring roe goes to Japan, and the carcasses are reduced for oils and meal.

The Pacific herring (Clupea harengus pallasi) is distributed throughout the coastal regions of both eastern and western shores of the Pacific Ocean. On the eastern shore, it is found from northern Baja California up to the Beaufort Sea. On the western side, it is found from Korea, north to the Arctic Ocean. The adults are found at depths of 100150 m. Juveniles are found between 150 and 200 m of water.

The Pacific herring spawn in the late winter through to April, with peak spawning occurring in March. This exclusive spring spawning distinguishes the Pacific herring from their Atlantic counterpart. Most are able to spawn by the time they are about three years of age. The spawning process is very dramatic as the fish broadcast eggs and sperm near shore. The water in which they spawn turns white with the milt from the males, covering as much as 257 km of shore line and at depths from the surface to about 10 m. The spawning area is usually in the intertidal zone, in sheltered bays or on open sand beaches, but not on exposed coastal areas. The texture of the substrate seems to be an important factor in determining the exact location of spawning.

The female produces between 9,000 and 38,000 eggs depending on her size, which can range from about 20 to about 30 cm. The relative fecundity is about 200 eggs per gram body weight per year. In extreme cases, fish can grow to 50 cm and produce over 100,000 eggs. The eggs are about 0.9 mm in diameter before fertilization but expands to about 1.2—1.5 mm in diameter after fertilization and the absorption of water. They are also very sticky once they are exposed to water. The eggs commonly adhere to aquatic plants such as eelgrasses or rockweed. The incubation time is about 10 days and the newly hatched alevins measure about 7.5 mm in length. The yolk is absorbed within the following two weeks and the fish then begin to feed on planktonic organisms. At that stage, the young do not resemble the adults. They are white, thin, and have large eyes. In about two months following yolk absorption, the young start to resemble the adult form and begin to form schools. By the late summer, the young are about 2.5-4.0 cm long and move to deeper waters in the fall. The Pacific herring can live to be 10 yrs old. During growth and maturation, they may be about 15 mm by the end of their second year, about 20 mm at the end of their fourth year, and about 23 cm at the end of the eighth year of life. They return to shallow waters close to shore as they mature sexually and prepare to spawn. They also tend to have a diurnal migration as rise to the surface in the evening and swim to deeper waters at dawn.

Atlantic Herring

The Atlantic herring (Cuplea harengus harengus) looks like its Pacific counterpart with iridescent blue or bluish green back and sides and a silver belly. Like the Pacific herring, its abundance has been declining steadily over time. The Canadian landings, for example, were 528,000 tons in 1968; 250,000 tons in 1975; 177,000 tons in 1980; and 147,000 tons in 1982. The advent of the highly efficient purse seine net has contributed to the harvest pressures on populations of herring. Gill nets, trap nets, and weirs have traditionally been used to catch herring. It is distributed on both sides of the North Atlantic Ocean. On the west side, it is found from Greenland south along the east coast of North America to Cape Hatteras. On the east side of the Atlantic, its distribution extends from Iceland, south to Europe between the White Sea to the Strait of Gibraltar.

Atlantic herring mature to spawn at three to five years of age. There seems to be several discrete stocks that spawn at different times of the year; there are spring, summer, and fall spawning populations. There may be stocks spawning every month between April and November throughout its distribution. Spring spawning occurs in shallower inshore areas, whereas summer and fall spawning occurs in deeper offshore waters. Like the Pacific herring, eggs and milt are broadcast into the open water where fertilization occurs. The eggs then sinks to adhere to bottom plants such as Irish moss and several algal species at depths of 1-4 m. The fecundity can range an order of magnitude from 23,000 to 261,000 eggs, depending on body size and age. The fecundity increases with body size and age up to a certain age, after which egg numbers decline with further aging. Fecundity is also a function of when spawning occurs. Spring spawners produce up to about half the egg numbers of summer and fall spawner. The eggs, however, have a larger yolk mass. This may reflect a strategy to survive the colder months of spring when food supply might be less abundant than in the summer and fall months. The small eggs, which measure from 1 to 1.5 mm in diameter, take from 10 to 30 days to hatch, depending on the ambient water temperature. The hatched alevins are about 4 mm long. They are light sensitive and avoid bright light, seeking deeper waters during the day. Unlike the Pacific herring that stay relatively close to their spawning grounds, Atlantic herring migrate offshore extensively.

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