Salmon Essay, Research Paper
What species would travel over 2000 miles just to have young and then die? It has been said that anyone who has not seen a wild salmon has not seen what a fish should be. Salmon was the common name applied to fish characterized by an elongated body covered with small, rounded scales and a fleshy fin between the dorsal fin and tail. In this paper I will be discussing history of studying salmon, the life cycle, spawning and mating behaviors; which has much to do with the total reproduction of salmon.
Salmon were studied earlier than some may think. Experiments were done by men that date back to the mid-1600s. These experiments involved catching salmon in fresh water, tagging them, and then catching them again when they return to the same place, around six months later. These experiments were doubtful and it was not until the beginning of the 1900?s that proof was available that the salmon returned home. (Shearer)
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 mating season, usually develops a hooked snout and a humped back. “In many diverse taxa, males of the same species often exhibit multiple mating strategies. One well-documented alternative male reproductive pattern is ‘female mimicry,’ whereby males assume a female-like morphology or mimic female behavior patterns. In some species males mimic both female morphology and behavior. We report here female mimicry in a reptile, the red-sided garter snake (Thamnophis sirtalis parietalis). This form of mimicry is unique in that it is expressed as a physiological feminization. Courting male red-sided garter snakes detect a female-specific pheromone and normally avoid courting other males. However, a small proportion of males release a pheromone that attracts other males, as though they were females. In the field, mating aggregations of 5-17 males were observed formed around these individual attractive males, which we have termed ’she-males.’ In competitive mating trials, she-males mated with females significantly more often than did normal males, demonstrating not only reproductive competence but also a possible selective advantage to males with this female-like pheromone.”
In the competitive mating trials, the she-males were successful in 29 out of 42 trials. The normal males won out in only 13! The authors ask the question: Why aren’t all males she-males given such an advantage?
(Mason, Robert T., and Crews, David; “Female Mimicry in Garter Snakes,” Nature, 316:59, 1985.)
Comment. Among the fishes, bluegills and salmon (and probably many others) have female-appearing males competing with normal males.
Abstract: The influence of sperm competition and individual mating behaviour in an externally fertilizing species of fish, the Atlantic salmon (Salmo salar), is estimated from video observations of multiple-male spawnings and subsequent paternity analyses. One male dominated the paternity during polygamous spawnings, fathering more than 80% of the progeny in a single nest. Behavioural analyses of the spawnings showed that the first-mating male had sperm precedence in 6 out of 10 cases. In three of the other spawnings, sperm limitation likely influenced individual success, as the first-mating male had participated in a large number of spawnings. In the final, nearly simultaneous spawning, male size was more important than the 0.6-s difference in spawning times. Thus, male fertilization success can be influenced by a variety of factors, including sperm precedence, male size, and spawning history. Back to Table of Contents
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 that precede mating, neither the females nor the males consume food.
In the life cycle of the pacific salmon, nature recycles the parents to feed the babies. Mature salmon leave the Pacific Ocean as saltwater fish, never again to eat as they battle their way up the Columbia River to spawn in the home stream where they were born. Those born in the upper reaches of the Columbia River’s tributary stream, the Snake River, travel more than 1,000 miles inland to lay their eggs and fertilize them, roughly one fourth of the distance across the United States. Without enough reserves
in their bodies to get back to the Pacific, the adult salmon spawn and die. To spawn, a female salmon scoops a nest in stream-bottom gravel by waving her tail and deposits her eggs in the hole. The male releases milt (sperm) into the water that covers the eggs and fertilizes them. Then the female brushes gravel over the eggs, and both parents lie exhausted in the stream until they die.
Micro-organisms in the water decompose their bodies during the winter, and this process increases the population of micro-organisms in the stream. Come spring, the salmon eggs hatch into the tiny fish called “fry.” The first food is the microorganisms in the stream. The Pacific salmon never see their parents, but are actually nourished by their decomposed bodies. The next step in growth is “fingerlings,” then young salmon make the dangerous trip downstream, past dams and waterfalls to the ocean. There they grow into adults, averaging six pounds in weight. In its life cycle, the pacific salmon takes
five forms and sizes: a pea-sized egg, one-half-inch embryo, one- to three-inch fry, four- to five-inch fingerling, and fully grown, six-pound adult one to two feet long. Nature fully recycles pacific salmon. (Atlantic Salmon, in contrast, travel up rivers only
150 to 250 miles long and can return to the sea after spawning.)
The males of many fish fight for the possession of the females. When a fish is conquered, his colors fade away and he hides his disgrace among his peaceable companions, but is for some time the constant object of his conqueror?s persecution. Mr. Shaw saw a violeny contest between two male salmon that lasted for a days. The males are constantly teare
“In many diverse taxa, males of the same species often exhibit multiple mating strategies. One well-documented alternative male reproductive pattern is ‘female mimicry,’ whereby males assume a female-like morphology or mimic female behavior patterns. In some species males mimic both female morphology and behavior. We report here female mimicry in a reptile, the red-sided garter snake (Thamnophis sirtalis parietalis). This form of mimicry is unique in that it is expressed as a physiological feminization. Courting male red-sided garter snakes detect a female-specific pheromone and normally avoid courting other males. However, a small proportion of males release a pheromone that attracts other males, as though they were females. In the field, mating aggregations of 5-17 males were observed formed around these individual attractive males, which we have termed ’she-males.’ In competitive mating trials, she-males mated with females significantly more often than did normal males, demonstrating not only reproductive competence but also a possible selective advantage to males with this female-like pheromone.”
In the competitive mating trials, the she-males were successful in 29 out of 42 trials. The normal males won out in only 13! The authors ask the question: Why aren’t all males she-males given such an advantage?
(Mason, Robert T., and Crews, David; “Female Mimicry in Garter Snakes,” Nature, 316:59, 1985.)
Comment. Among the fishes, bluegills and salmon (and probably many others) have female-appearing males competing with normal males.
Abstract: The influence of sperm competition and individual mating behaviour in an externally fertilizing species of fish, the Atlantic salmon (Salmo salar), is estimated from video observations of multiple-male spawnings and subsequent paternity analyses. One male dominated the paternity during polygamous spawnings, fathering more than 80% of the progeny in a single nest. Behavioural analyses of the spawnings showed that the first-mating male had sperm precedence in 6 out of 10 cases. In three of the other spawnings, sperm limitation likely influenced individual success, as the first-mating male had participated in a large number of spawnings. In the final, nearly simultaneous spawning, male size was more important than the 0.6-s difference in spawning times. Thus, male fertilization success can be influenced by a variety of factors, including sperm precedence, male size, and spawning history. Back to Table of Contents
An adult female salmon can lay upto 15,000 eggs, depending upon her size.
The female fish (hen) creates a depression in the gravel bed of the river by an energetic flapping of her large tail. The male (cock) fish swims up beside her and begins to quiver, stimulating the female to release her eggs, at the same time the male releases his milt which fertilises the eggs. Once the mating has been completed the female again starts to beat the river bed with her tail, this time just above the site where she laid her eggs, this causes gravel to wash downstream with the current and cover the eggs.
This covering of gravel offers the eggs protection from predators such as eels, ducks and other fish.
After spawning, the male fish, now called a kelt, rapidly loses the hooked jaw and bright colouration that it had developed just prior to the mating season. The male may remain at the breeding site for days or weeks, guarding the newly-layed eggs.
Salmon eggs deposited in the autumn hatch the following spring
The Atlantic and Pacific salmon demonstrate distinctly different reproductive strategies. The Atlantic salmon may return to fresh
water to spawn several times while the Pacific salmon concentrates its reproductive efforts into one large spawning event and
then dies (Ward, 1939).
The reproductive cells of the Pacific salmon all mature simultaneously and as a result, these fish have only one chance to breed.
With the completion of spawning, their lives soon come to an end. Although the Atlantic salmon has the physiological potential
to reproduce numerous times, the long journey to the spawning grounds, as well as the stress of the reproductive act itself takes
its toll. Typically, fewer than 10 per cent of spawning Atlantic salmon return to the ocean, with most of these being females.
These fish belong to the salmon family. Most members of this family are valuable food and a source of excellent game. They are found in both fresh and salt water in the colder regions of the Northern Hemisphere. Many return from salt water to freshwater to breed, and the young migrate to salt water from freshwater 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 freshwater 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.
1. Mills, Derek. (1989). Ecology and Management of Atlantic Salmon. New England,
New York: Chapman and Hall.
2. Shearer. (1978). The Atlantic Salmon. New York: Halsted Press form
3. Cone, J., & Ridlington, S. (Eds.). (1996) The Northwest Salmon Crisis: A documentary History. Corvallis, Oregon: Oregon State University Press.