(Biol 207) Freshwater Biology 1996
Contents: A. Abstract B. Introduction C. Taxonomy D. Types of Pacific Salmon E. Habitat Description E. (a) Distribution F. Reproduction G. G. Feeding Habits & Adaptations H. Ecological Role I. Locomotion J. Interactions with other organisms K. Issues Concerning Hydroelectric Dams ____________________________________________________________________
Abstract:
Several aspects and features of the Pacific salmon were reviewed and examined through literature research. The features and aspects that this literature focused on were homing, migration, osmoregulation, reproduction, locomotion, ecological role, and feeding habits. Factors involving Pacific salmon population decline were also reviewed. Salmon play an important role in the food chain as well as an indicator of the health of the forest ecosystem. Therefore solutions must be made to control or prevent the human made problems from further damaging the Pacific salmon population where one day they may become extinct.
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Introduction:
There are five types of Pacific salmon species: chinook, coho, sockeye, pink, and chum. Pacific salmon are anadromous fish. Each year, after hatching from the eggs laid in the gravel beds of upstream, they grow into smolts, or young fish that are carried downstream by the current of their natal streams and spewed into the sea (Eley & Watkins 1991). The ocean becomes their home where they feed and grow. Upon reaching maturity in the ocean, they return to their natal stream to spawn and complete their life cycle. This journey involves fighting desperately against the current, surmounting cascades and even waterfalls with spectacular wriggling leaps, evading predators, until exhausted, they find the place where instinct tells them to spawn and then die (i.e. Eley & Watkins). All of the five types of Pacific salmon have similar life histories. However, each type of salmonid specie has its own natural history, habits and relative abundance.
There are many issues concerning the declination of Pacific salmon population, and some species of Pacific salmon may face extinction. Hydroelectric dams are one of the major concern in the decline of salmon population. This issue is reviewed in this scientific paper.
Taxonomy:
Kingdom = Animalia
Phylum = Chordata
Class = Osteichthyes
Order = Salmoniformes
Family = Salmonidae
Genus = Oncorhynchus
Specie = kisutch
Salmon belong to the Animalia Kingdom because they are multicellular eukaryotic organisms that are able to feed and digest whatever they prey on. They have a notochord and nerve chord; hence they belong to the Chordata phylum. They have a bony structure; therefore, they are a member of the Osteichthyes (bony fish) class. Salmons, trouts, chars, and whitefishes all belong to the order of Salmoniformes and family of Salmonidae (Scott and Scott 1988). Lastly, all salmon are members of the genus Oncorhynchus (Greek for "hooked nose") (Eley and Watkins 1991). The specie category differentiates the different kinds of Pacific salmon by their physical characteristics. Coho salmon belongs to the specie kitsutch because of its defined phenotypic traits of that specie.
Types of Pacific Salmon:
There are five kinds of Pacific salmonid species, and they are sockeye salmon (Oncorhynchus nerka) , pink salmon (Oncorhynchus gorbuscha), coho salmon (Oncorhynchus kisutch), chinook salmon (Oncorhynchus tschawytscha), and chum salmon (Oncorhynchus keta). The life histories of Pacific salmon are very similar (Hart 1973), and it is a vigorous adventure that each salmoniod specie must face. Pacific salmon are fascinating fishes that are able to live in both salt water and freshwater environments. They only spend their breeding and nursery period in the freshwater environment (Hart 1973). Salmon spend most of their life in the salt water (ocean), but their dependence on freshwater is also a necessity for the survival of further generations (Childerhose & Trim, 1979).
Habitat Description:
The Pacific salmon is an anadromous species that spends most of its life at sea, and it can also live in freshwater lakes. Depending on the specie, Pacific salmon may spend from one week to 36 month in freshwater before migrating toward the sea (WWW-fishfaq2d.html). In the freshwater environment, the young salmon spends most of its time in rivers, streams and lakes that serve as nursery grounds for them (e.g., Scott & Scott 1988). Some salmon may be landlocked due to natural land obstruction that blocks the salmon from reaching the sea water to mature. These salmon and those who choose to simply remain in freshwater still follow the same life cycle and die after spawning (e.g., Scott & Scott 1988). The habitats that salmon fries live in are large cool rivers with extensive gravely bottom headwaters (e.g., Childerhose & Trim 1979). Salmon are cold-blooded animals and the amount of food they require to sustain themselves increases with rising temperature. Above 15.5(C the fry may have trouble finding enough food and at the same time their resistance to disease falls off (Childerhose & Trim 1979). Around 24(C the young salmon will die from temperature alone (Childerhose & Trim 1979). The gravel substrate and water temperature are important factors that control the fate of the young salmon.
Gravel has important purposes to the salmon's life cycle. Salmon rely on this substrate for egg incubation and serve as a protection ground for the fries when hatched (van den Berghe & Gross, 1989). The size of the gravel that is chosen is important for spawning. Large size gravel may not hold the eggs in place in current flow, and fine sediments may impede current flow through the gravel, restricting oxygen availability and sometimes precluding physical emergence of the fry (van den Berghe & Gross, 1989). It has been estimated that poor gravel kills 46 to 87% of eggs deposited by Pacific salmon (van den Berghe & Gross, 1989).
Salmon spend from one to four years feeding and maturing in the ocean (Childerhose & Trim 1979). When at sea, they seem to prefer water temperatures of 4-12(C (Scott & Scott 1988). Salmon travel together in the ocean and stay in areas that contains large amounts of food (Scott & Scott 1988).
Distribution:
The oceanic distribution of the Pacific salmon is dependent upon the species and point of origin. Between fall and midwinter, Pacific salmon juveniles leave the coastal belt to make a continuous wide sweep around the rim of the Gulf of Alaska (Childerhose & Trim 1979). Sockeye and chinook salmon from the northwest Alaska, for example, may migrate across the Bering Sea to areas close to Kamchatka, USSR, and the south of the Aleutian Islands into the North Pacific Ocean; the sockeye also migrate eastward to the Gulf of Alaska (WWW-fishfaq2d.html). Salmon such as pink, chum, and coho from the central and southeast Alaska, British Columbia, and Washington State, migrate out into the northeastern Pacific and Gulf of Alaska (WWW-fishfaq2d.html). A chinook salmon tagged in the central Aleutian Islands and recovered a year later in the Salmon River, Idaho, had traveled about 3,500 miles (WWW-fishfaq2d.html).
Reproduction
The spawning period varies according to the type of salmoniod specie. Pacific salmon seem to spawn only during the spring, summer, and fall (Maxwell 1995). Pacific salmon only spawn once in their lifetime because soon after spawning the all die. Therefore it is very important for the adult females to produce as many successful nests as possible, and it's also important for the adult males to mate with as many females as possible to ensure successful nest fertilization. Pacific salmon develop morphological breeding characteristics as the mature in the ocean. In their homing migration period, they develop bright coloration, hooked snouts, large caninelike teeth and humped backs (e.g., Fleming & Gross, 1994). Their change in body coloration from silvery marine state to bright red along the sides may function as an intrasexual or intersexual signal (Fleming & Gross, 1994).
There is a strong competition among the male salmon as well as the female salmon to reproduce successfully. Males are generally larger than females (447 versus 428 mm) and have larger dorsal humps and more elongated jaws for their length(Quinn & Foote,1994). In Pacific salmon, females establish oviposition territories in freshwater streams and sequentially construct several nests, collectively called a redd (Fleming & Gross 1994). Females require approximately 2.7m2 of gravel substrate for nesting (van den Berghe & Gross 1989). Eggs are spawned in gravel substrate where the female establishes a territory and sequentially constructs several nests. Within each nest the female releases a portion of her eggs that are fertilized by one or more males (Gross 1985). Males compete for temporary access to these spawning females, with size being the major factor in such reproduction interactions (e.g., Kennleyside & Dupuis 1988). This extra fertilization and size factor of the male salmon help to increase the chance of successful mating. Quinn and Foote (1994) found that males of larger body size and with relatively larger dorsal humps obtain higher status on the spawning grounds than smaller males and thus appeared to be favored by sexual selection. However, The inability to acquire a territory reduces a female's ability to spawn all her eggs prior to death (Fleming & Gross, 1994). After spawning, female salmon guard their territory to prevent reuse and destruction of her eggs by later-arriving females (van den Berghe & Gross, 1989). Once the female salmon grows weak or uses up her body fat during her guarding of her nest she will drift downstream and eventually die.
Eggs hatch several months later and the juveniles establish feeding territories. The fry migrates to the downstream to nursery lakes. The nursery bed of lakes will provide the protection as well as the feeding ground for these young salmon. Depending on the specie, juvenile salmon stay in the freshwater environment from one week to 36 months before migrating to sea (WWW- fishfaq2d.html). During this nursery period, the fry stays around the gravel bed for protection and feed on plankton and larvae aquatic insects. The growth rate is slow when the young salmon are in freshwater, but once they migrate to the sea the growth rate is rapid (Childerhose & Trim 1979). However, it has been found that larger salmon eggs produce larger fry that grows faster (van den Berghe & Gross, 1989).
Osmoregulation:
Salmon that migrate between sea water and freshwater undergo a transition in their osmoregulation. A marine fish is hypoosmotic to the surrounding sea water and therefore constantly loses water by osmosis. While in the ocean, salmon drink large amounts of sea water to compensate for the loss of water by osmosis and then excrete excess salt by using specialized cells to pump it out of the body across the gill epithelium (Campbell 1993). Excess concentration of salts is also believed to be excreted through urine.
As the juvenile salmon is migrating toward the sea or when the adult salmon is homing to the freshwater stream to spawn they both are face with the problem of being hyperosmotic to the surroundings. Being hyperosmotic to the surroundings the salmon constantly gain water from its surrounding through osmosis. This water uptake is balanced by the copious excretion of urine, which is hypoosmotic to the body fluids of the salmon (Campbell 1993). Although the urine is dilute, the animal still loses important salts during excretion and compensates by the active uptake of ions across the epithelium of the gills (Campbell 1993).
Migration
Salmons need the freshwater rivers, lakes, and tributaries not only for breeding but also for incubation of their eggs and the survival of their young or fries (Childerhose & Trim, 1979). The young or fries must stay in the nursery streams, and lakes until they are strong enough to migrate out to the sea (Childerhose & Trim, 1979). The offspring migrate to the ocean, presumably to take advantage of increased productivity and foraging opportunities (Gross et. al 1988). Depending how far the ocean is, some juvenile salmon migration could mean traveling hundreds of kilometers away from natal home. The seaward migration period involves the juvenile salmon having to travel through diverse habitats such as rivers and lakes in order to arrive at the open ocean. During their seaward migration, juvenile salmon learn (imprint on) odors associated with their natal site and later, as adults, use these odor memories for homing (Dittman & Quinn, 1996).
Homing
Depending on the specie of salmon, one or more years later, they leave the safety of the ocean to return to the shallow inshore waters near the mouth of their home river. Pacific salmon are famous for their homing migrations from oceanic grounds to their natal river to spawn. This feat of homing is believed as the most vigorous adventure of the salmon's life cycle. The upstream migration may take several weeks or more depending on the distance they have traveled during their migration to the sea. During these migrations, salmon travel through diverse habitats (e.g., oceans, lakes, rivers), each offering distinctive orientation clues and, perhaps, requiring distinctive sensory capabilities for navigation (Dittman & Quinn, 1996). This odyssey of the pacific salmon requires a remarkable feat of endurance and it's the reason that they die after spawning .
Death
All Pacific salmon species soon die after spawning. Their death is related to several factors. In the scientific book, written by R. J. Childerhose and Marj Trim, explained that a death relating factor is deterioration which starts with the onset of sexual maturity in the ocean. He believed that all the glands of the salmon appear to be affected, but especially the pituitary and adrenals. When the ritual of courtship and spawning is completed, there is a rapid aging of the salmon's body in all its parts: blood, tissue, and organs (Childerhose & Trim, 1979). Death results from this extreme acceleration of glandular activity.
Another factor that contributes to the death of Pacific salmon soon after spawning is the lack of feeding. In the scientific literature, written by Jessica Maxell, explained that salmon does not feed during their upstream migration. Instead, they depend on their stores of fat to reach their destination; hence, they die because their bodies used up by the exertion of procreation (Maxwell 1995).
Locomotion:
Pacific salmon are ray finned fishes which have fins that are mainly supported by long flexible rays (Campbell 1993). Salmon have several fins that are used for maneuvering. These various fins are: low pectoral fins, abdominal pelvic fins, dorsal fin, adipose fin (characteristic of salmonidae), anal fin, and the caudal fin. The low pectoral fins are used in steering, turning, braking, and maintaining balance. The abdominal pelvic fin, dorsal fin, and the anal fin are used mainly for steering and position stabilization of the fish. All salmon have a swim bladder which is a specialized air sac organ that serves as a buoyancy control center for the salmon. It functions by regulating the amount of gas transferred between the organ and blood resulting in the inflation or deflation of the bladder; hence, adjusting the density of the fish. This air sac organ helps the salmon to conserve energy from having to use excess energy for buoyancy control.
The salmon's main mean of locomotion is the caudal fin. This muscular tail fin helps to propelling the salmon forward. Although, salmon's body is mainly composed of muscles it has specialized muscle movement so that the muscles are not over worked. This specialized muscle movement is angulation. Angulation is basically the propelling or gliding of the salmon through the water by a rhythmic muscle contraction of its body. This angulation mechanism requires less energy expenditure of the salmon.
Feeding Habits/ Adaptations:
The feeding habit of Pacific salmon varies, each having its own diet at the different stages of the life cycle. In general, at sea, Pacific salmon feed on squids, a variety of small fishes (such as herring, smelts, alewives, capelin, small mackerel, small cod), plankton (euphausiids), amphipods and decapods (Smith 1985). In the freshwater, juvenile salmon mainly eat the larvae of aquatic insects such as blackflies, stoneflies, caddisflies, chironomids, and others (Smith 1985). Terrestrial insects are important part of the salmon's diet during the summer when these insects are abundant (Scott & Scott 1988). If the juvenile salmon are large then small fishes becomes an important part of their diet in the freshwater (Scott & Scott 1988). Small fishes also become part of the maturing salmon's main diet at sea (Scott & Scott 1988).
The juvenile salmon adapts to a seasonal progression in their diets until they are large enough to prey on larger organisms like small fishes (Scott & Scott 1988). In the spring they will feed mainly on aquatic larvae insects, in the summer they feed mainly on terrestrial insects, and toward the end of summer they will start feeding on small fishes (Scott & Scott 1988). Prior to spawning, mature adults acquire as much fat as possible through feeding on small fishes; they do not eat after they re-enter freshwater to spawn (Scott & Scott 1988).
Interaction with other organisms:
Young Pacific salmon and adult salmon fall prey to many other animals. When young they are preyed upon by larger fishes and birds. Gulls and cormorants are probable predators on smolts when first going to sea (Scott & Scott 1988). Birds and small animals such as mergansers, kingfishers, heron, gulls, mink, and otter find them easy prey (e.g., Scott & Scott 1988). Eels are also known to eat large numbers of young salmon (e.g., Scott & Scott 1988).
At sea, salmon remains have been identified from the stomachs of harbor seals, grey seals, sharks, pollock, and tuna (Scott & Scott 1988). Homing salmon sometimes fall prey to bald eagles, ospreys and bears. During their upstream run, grizzly bears await by the river and stream to prey on the salmon (Childerhose & Trim 1979). The predators that prey on returning salmon are extremely high during the salmon's spawning period (Childerhose & Trim 1979). Salmon also preyed upon by fisherman to supply the fish market.
Ecological Role & Importance:
Salmon are important part of the food chain. They are important diets to many birds and small animals. Native Coast Indians still depend on the salmon for a large part of their diet (Maxwell 1995). Pacific salmon are becoming extinct in numbers due to damage done by dams, logging, overfishing, degrading habitat, and the resultant loss of both genetic variability and the life history (Maxwell 1995). If these problems or human hazards are not prevented or controlled then the Pacific salmon will face extinction and an important part of the food chain is lost. There are solutions that have been carried out to prevent extinction of Pacific salmon. On April 8, 1994, tribal, federal, and state fish management agencies agreed to shut down fishing for all coho and most chinook salmon, both offshore and in rivers of Washington and Oregon (Maxwell). Money has been raised to replace the salmon spawning gravel washed away by water released by dams (Maxwell 1995).
Issues Concerning Hydroelectric Dams:
There have been many issues concerning the decline of Pacific salmon population. Worsening freshwater (spawning) habitat has been a significant cause of the salmon decline. This includes siltation problems and, particularly, the lack of water for spawning and fish passage (www-unit12.html). Hydroelectric dams have been a major factor in further declines of salmon population.
Eley and Watkins (1991) found that 90% of young salmon are lost on the downstream run, mainly, because the ladders of the hydroelectric dam were designed to let adult salmon move upstream and did not allow for the return journey. Instead of being carried downstream by the natural current, the juvenile salmon more often get mutilated in unscreened generating equipment, get trapped inadequately designed screens, or languish in reservoirs until they die from predation, heat, or disease (Eley & Watkins 1991). It has been suggested by many environmentalists that Dams without ladders should get them and existing fish ladders should be modified to facilitate the passage of fish in both directions (e.g., WWW-unit12.html).
Suggested Web Sites to visit to learn more about Pacific salmon:
Distribution Of Chinook Of The North Pacific Address: http://www.cqs.washington.edu/~hinrich/npacific_dist.html
Salmon Life History Address- http://www.cqs.washington.edu/~hinrich/lifehistory.html
Where Do Salmon Go In The Ocean Address - http://www.wh.whoi.edu/faq/fishfaq2d.html.
References:
Campbell, Neil A. 1993. Biology. Third Edition. The Benjamin/Cummings Publishing Company, Inc. California.
Childerhose, R.J., and Trim, Marj. R.J. Pacific Salmon & Steelhead Trout. Vancouver: Douglas & Mcintyre Inc. 1979.
Dittman, Andrew H., and Quinn, Thomas P. 1996. Homing in Pacific Salmon: Mechanisms and Ecological Basis. The Journal of Experimental Biology. 199: 83-91.
Fleming, Ian A., and Gross, Mart R. 1994. Breeding competition in a Pacific salmon (coho: Oncorhychus kisutch): measures of natural and sexual selection. Evolution 48: 637-657.
Eley, Thomas J., and Watkins, T. H. 1991. In a sea of trouble (the uncertain fate of the Pacific salmon). Wilderness 55: 18-26.
Gross, Mart R. 1985. Disruptive selection for alternative life histories in salmon. Nature 313: 47-48
Hart, J. L. 1973. Pacific fishes of Canada. Fisheries Research Board of Canada. Bulletin Number 180.
Keenleyside, M. H., and Dupuis, H. M. C. 1988. Courtship and spawning competition in pink salmon (Oncorhynchus gorbuscha). Canadian Journal of Zoology 66: 262-265.
Maxwell, Jessica. 1995. Swimming with salmon. Natural History 104: 26-39.
Scott, W.B., and Scott, M.G. Altantic Fishes of Canada. University of Toronto Press. Canada. 1988.
Smith, C. Lavett. The Inland Fishes of New York. New York State Department of Environmental Conservation. New York. 1985.
Quinn, Thomas P., and Foote, Chris J. 1994. The effects of body size and sexual dimorphism on the reproductive behaviour of sockeye salmon, Oncorhychus nerka. Animal Behavior 48: 751-761.
Van Den Berghe, Eric P., and Gross, Mart R. 1989. Natural selection resulting from female breeding competition in a pacific salmon (coho: Oncorhychus kisutch). Evolution 43: 125-140.
WWW Cites:
Fishfaq2d.html, Address - http://www.wh.whoi.edu/faq/fishfaq2d.html. Where do salmon go in the ocean. Visited on Oct. 21, 1996.
Unit12.html, Address - http://kingfish.ssp.nmfs.gov/olo/unit12.html. Visited on Oct. 21, 1996.