|
A Little Bit About
Salmon:
Salmon (fish), common name
applied to fish characterized by an elongate body covered with small
cycloid (rounded, with smooth edges) scales and possessing an adipose
(fleshy) fin between the dorsal fin and tail. These fish belong to the
salmon family. Most members of this family are valuable food fish and
excellent game fish. They are found in both fresh and salt water in
the colder regions of the northern hemisphere. Many return from salt
water to fresh water to breed, and the young migrate to salt water
from fresh water after they reach maturity. The migratory instinct of
members of the salmon family is remarkably specific, each generation
returning to spawn in exactly the same breeding places as the
generation before it. Even those species that do not migrate from
fresh water to salt water spawn in the same freshwater streams as did
their ancestors. The spawning ground of these fish is usually a
rapidly flowing, clear stream with gravel and rocks on the bottom.
Salmon Breeding and
Nests:
Although usually drab in
color before the breeding season, which varies with the species,
members of the salmon family develop bright hues at spawning time. The
male, during this season, usually develops a hooked snout and a humped
back. Before mating, one parent excavates a nest for the eggs; after
the eggs are deposited and fertilized, the female stirs up the stream
bottom so that earth and stones cover the eggs and protect them. The
eggs hatch in two weeks to six months, depending on the species and
the water temperature. During the migrations and nest-building
activity preceding mating, neither the females nor the males consume
food.
Members of the salmon family
subsist on smaller fish, crustaceans, and insects. In addition to the
true salmon, the salmon family also contains many species known as
char (see Trout); zoologists also include the grayling and whitefish,
which are similar in structure, in the salmon family.
Atlantic Salmon:
The true salmon, the largest
members of the salmon family, are characterized by tasty flesh that is
often orange-red. The common salmon of the North Atlantic Ocean that
is sent to market averages about 7 kg (about 15 lb) in weight, but
specimens weighing more than 45 kg (more than 100 lb) have been
caught. The Atlantic salmon migrates to cold, fresh water in late
spring or early summer, swimming upstream at an average rate of up to
6.4 km (4 mi) per day. Because salmon can jump as much as 3.7 m (12
ft) out of water, they clear most obstacles in their path. The female
lays as many as 20,000 eggs in October or November, after which time
the adult salmon float downstream and return to the sea.
Unlike the various species
of Pacific salmon, the Atlantic salmon does not die after its first
spawning but returns year after year to its breeding place. The newly
hatched young, which are known as parrs or brandlings because of the
dark transverse markings on their sides, remain in fresh water for
about two years. At this time, the young, which are known as smolts
and which have become silvery in color, descend to the sea. Upon the
first return of the Atlantic salmon to its spawning ground, the fish
is known as a grilse. After spawning, it is known as a kelt.
Several subspecies of the
Atlantic salmon live in the lakes of the northern United States
without ever descending to sea; such salmon are known as landlocked
salmon. Landlocked salmon are much smaller than are migrating salmon,
attaining a maximum weight of about 35 pounds. The two most important
landlocked populations of the Atlantic salmon are the Sebago salmon,
found from New Hampshire to New Brunswick, and the ouananiche, of Lac
Saint-Jean, Canada.
Pacific Salmon:
Salmon found in the North
Pacific Ocean spawn only once, dying after depositing and fertilizing
their eggs. The best-known and most valuable species is the chinook
salmon, which is also known as the king salmon, Columbia River salmon,
quinnat, chowichee, and takou. Market specimens of this fish average
about 9 kg (about 20 lb) in weight, but numerous specimens more than
1.5 m (more than 5 ft) in length and well over 45 kg (more than 100
lb) in weight have been recorded. The chinook salmon migrates farther
than any other salmon, often traveling 1600 to 3200 km (1000 to 2000
mi) inland to its spawning ground. Its eggs usually hatch within two
months, and the young descend to the sea when 5 to 7.5 cm (2 to 3 in)
long. The sockeye, red, or blueblack salmon is another valuable
species, as is the coho, or silver salmon, which has light pink flesh.
Other salmon in the Pacific basin are commonly known as the pink, or
humpbacked salmon, and the chum, or dog salmon.
Anglers fish for salmon with
rod and reel, often using flies as bait. Commercial fishing for salmon
is done on a much larger scale, employing traps and pound nets to
catch the fish on the way to their spawning grounds. Salmon canning is
one of the major industries of the American Pacific coast. To mitigate
the decimation of wild salmon runs caused by construction of dams and
overfishing, the U.S. Fish and Wildlife Service yearly deposits
billions of salmon eggs and young, propagated in nurseries, into
natural breeding grounds and constructs fish ladders for the upstream
journey of mature salmon. However, hatchery-raised salmon have
aggressive feeding habits-that is, they spend most of their time at
the water's surface looking for food unlike the wild salmon that spend
most of their time in deep water or under cover. As a result,
hatchery-raised salmon consume most of the food wild salmon need to
live. At the same time, this aggressive feeding makes hatchery salmon
more vulnerable to predators because they stay near the surface.
Hatchery salmon usually have less genetic diversity (see Genetics:
Genes in Populations) than wild salmon, which can lead to lowered
resistance to disease and other environmental hazards. The annual
harvest of wild and farm-raised salmon in the United States averages
about 478,000 metric tons, of which about 60 percent is canned. |
