Salmon, trouts and chars

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Taxonomy

Salmoninae (salmon, trouts and chars) is one of subfamilies of the family Salmonidae, which contains also subfamily Coregoninae (whitefishes) and subfamily Thymallinae (graylings) The subfamily contains many economically important species. Atlantic salmons are represented by one species, Salmo salar. Some Pacific salmons are:

• Oncorhynchus tshawytscha (Chinook salmon) - 10 to 15 pounds, up to 135 pounds,
• Oncorhynchus keta (chum salmon) - 10 to 15 pounds, up to 33 pounds,
• Oncorhynchus kisutch (coho salmon) - 6 to 12 pounds, up to 31 pounds,
• Oncorhynchus nerka (sockeye salmon) - 5 to 8 pounds, up to 15 pounds,
• Oncorhynchus gorbuscha (pink salmon) - 3 to 5 pounds, up to 12 pounds.

Some species that can be found in Great Lakes:

• Oncorhynchus tshawytscha (Chinook salmon),
• Oncorhynchus kisutch (coho salmon),
• Oncorhynchus mykiss (rainbow trout),
• Salmo trutta (brown trout),
• Salvelinus namaycush (lake trout),
• Salmon salar (Sebago or landlocked salmom) - not native.

Taxonomic lineage

cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Coelomata - Deuterostomia - Chordata - Craniata - Vertebrata - Gnathostomata - Teleostomi - Euteleostomi - Actinopterygii - Actinopteri - Neopterygii - Teleostei - Elopocephala - Clupeocephala - Euteleostei - Protacanthopterygii - Salmoniformes - Salmonoidei - Salmonidae - Salmoninae:
Brachymystax lenok (lenok)
Hucho spp. (taimen)
Oncorhynchus spp. (trouts and salmons)
Parahucho perryi spp. (Japanese huchen)
Salmo spp. (trouts and salmons)
Salvelinus spp. (chars and trouts)
Salvethymus svetovidovi (long-finned charr)

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Brief facts

Distribution

Atlantic salmon (salar means "leaper" in Latin) is a fish native to the basin of the North Atlantic Ocean, from the Arctic Circle to Portugal in the eastern Atlantic, from Iceland and southern Greenland, and from the Ungava region of northern Quebec south to the Connecticut River.

The oceanic distribution of the Pacific salmon depends on the species and point of origin. Between fall and midwinter, Pacific salmon juveniles leave the coastal areas and sweep around the rim of the Gulf of Alaska. Sockeye and Chinook salmon from the northwest Alaska, for example, may migrate across the Bering Sea to areas close to Kamchatka, and the south of the Aleutian Islands into the North Pacific Ocean. 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. A Chinook salmon can travel 3,500 miles from the central Aleutian Islands to the Salmon River, Idaho.

Anandromous and landlocked salmonids

Salmonids are typically anandromous (sea-run): they pass the major part of their life in salt water and ascending fresh water streams to find spawning grounds. However, in some of the river systems that carry these salmon, certain fresh water lakes that border the northern Antlantic and Pacific oceans contain salmon, which never run to salt water. They are generally recognized as landlocked salmon. These fish descended from seagoing kind and sometimes look very similar but usually smaller and often referred to as dwarf salmon.

Aquaculture and conservation

The Atlantic salmon is renowned sport game and food fish. Nearly 5-fold increase in global marine catch over four decades greatly depleted wild population of this long-lived species. Because of the strong market demand, an active aquaculture industry, which involves cage-rearing, hatcheries, and some sea ranching, has been developed all over the world. Aquaculture now accounts for over 30% of the world's fish market and about half of store-bought salmon. Initially, salmon farming was thought to decrease over-exploitation of wild populations and their rapid decline, which put Atlantic salmon on the list of endangered species. Yet the solution once hailed as a panacea has come under fire for threatening wild populations even further. Just a few reasons:

• farming carnivorous fish like salmon depletes wild stocks of other species (on average, every pound of farmed salmon consumes three pounds of wild-caught fish);
• fish farms foul coastal waters with organic and chemical contaminants, including feces, surplus additive-laden feed, antibiotics, pesticides, toxic antifouling paints, and disinfectants;
• millions of salmons escaped from the farms each year reduce survival rates of wild populations by competing for mates and diluting their genetic makeup through hybridization;
• aquaculture operations established on the migratory path of juveniles dramatically reduce survival rates of wild salmonids that migrate past them on their way to the ocean by exposing them to parasites, bacterial and viral diseases as well as pollutants to which they are susceptible to a greater degree than their farmed counterparts; in many cases, survival and returns to natal spawning grounds was estimated to drop by over 50% per generation.

Role of salmonids in fresh water and terrestrial ecosystems

Salmon's impact on terrestrial ecosystems is enormous and results from salmon migratory activities when it moves inland in great quantities thus interfacing with terrestrial life - carnivorous mammals, scavengers, numerous decomposers, and finally, plants. The influx of salmon biomass (i.e. carbon, nitrogen, phosphorus, calcium and other essential elements) entering fresh water from the ocean estimated in tens of thousands of tons.

One study estimates that in British Columbia (Canada) during the salmon spawning run, salmon might make up to 40-70% of wolf diet. In addition to safety benefits (selecting benign prey such as salmon over potentially dangerous ungulate prey like deer), salmon also provides enhanced nutrition over deer, especially in fat and energy: wolves selectively consume lipid-rich heads and potentially benefit from docosahexaenoic acid, an omega-3 fatty acid, which is critical for reproductive and nervous systems. Finally, for equivalent energetic intake, wolves face less hunting time and need to travel far less for salmon compared with searching for deer. In terms of the energy expenditure (nutrition and energy spent while hunting) salmon is far superior to deer: average wolf requires about 2.7 kilograms of deer daily whereas only 0.62 kg of pink salmon each day is sufficient for adequate nutrition.

Consequently, shift in wolves' diet in the fall, might ease their predatory pressure on the wild deer population allowing juvenile deers to grow in relative safety and reach maturity with greater probability.

While preying on migrating salmon, bears and wolves indirectly provide a considerable proportion of carcasses to a diversity of terrestrial scavengers and carnivores. While wolves target head tissue and usually forgo body, bears target brains and eggs, and under conditions of relatively low salmon abundance also consume musculature. Consequently, all remaining tissue would be available to scavengers immediately.

Salmon-derived nutrients are distributed widely throughout the terrestrial ecosystem by predators and scavengers transporting chunks of salmon's flesh far from the stream and into the forest, by flying adult stages of aquatic scavenging insects, with feces, with seeds of plants that completed their life cycle along the river and many other less investigated routes.

In conclusion, importance of salmonids in fresh water and terrestrial ecosystem has two aspects: 1) direct consumption of salmon as food, and 2) recycling of the products of decomposition, leaching and excretion.

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Life history (life cycle)

Typically, salmon are anadromous: they are born in fresh water, migrate to the ocean, then return to fresh water to reproduce. The major difference between Atlantic and Pacific salmons is that Atlantic salmon may spawn more than once while Pacific salmons die soon after one spawn.

• fertilized egg In fall female salmon lays 3,000-7,000 eggs, whic can constitute more than 20% of her body mass, in a nest called redd; it may take several days for hen salmon to lay all her eggs and cover them over with gravel. Prior her death, the female defends her redd to prevent reuse and destruction of her eggs by later-arriving females. The length of time fish live on the spawning grounds is generally less then 3 weeks. Eggs will overwinter.
• eyed ova After a few week after eggs were laid and fertilized, tiny black eyes appear inside the ova, soon afterwards the heart and other internal organs become visible.
• larval Also called alevin; this is stage of salmon between hatching from the egg and emergence from the stream gravel as a fry; the stage is characterized by the presence of a yolk sac, which provides nutrition while the larva develops in the protected gravel riverbed.
• fry Very young salmons which yolk sac had been absorbed; salmon fry hide under stones and among vegetation where they are able to avoid predators. Later the fry migrates downstream to nursery lakes. During this nursery period, the fry stays around the gravel bed and feed on plankton and larvae aquatic insects such as such as blackflies, stoneflies, caddisflies, chironomids, and others.
• parr Juvenile fish several months old; the young salmon develops noticeable markings that look like finger marks, along their flanks; parr live among boulders and beside submerged weed beds in the shallow water; parr feed for at least one year, more normally 2 and occasionally 3 years before they are ready to go out to sea; at that time they are typically about 6 inches long. At this point small fishes become an important part of their diet.
• pre-smolt The period during which salmon undergoes parr-smolt transformation that involves a complex metamorphosis from a freshwater-dwelling parr to a pre-adapted seaward-migrating smolt; this transformation involves a series of inter-related morphological, physiological, biochemical and behavioral changes; the smoltification process is a stressful period in the life cycle of salmon and the fish are immunocompromized during this time.
• smolt This is a juvenile salmon that is at least one year old and has adapted to marine environment; when the salmon parr begin to migrate to the sea, usually in March, April and May, they gradually become more elongated and their fins darken; a layer of guanine crystals is laid down in the skin, rendering the body more silvery in color and obscuring spots. One conspicuous behavioral pattern of landlocked salmonids is that when the surface water of the lake passes 10°C, the fish which have been continuously at or near the surface descent into deeper cooler layers.
• adult As smolts continue their voyage to ocean habitat they grow into fully developed adult salmons; depending on the species, salmon will spend from one to five years in the ocean and travel thousands of miles before returning to their natal stream (the stream where they were hatched); some fish stray to nearby rivers, colonizing new areas and replenishing weak populations. In general, at sea, salmon feeds on squids, a variety of small fishes (such as herring, smelts, alewives, capelin, small mackerel, small cod), and plankton.
• homing 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 ocean. During these migrations, salmon travel through diverse habitats - oceans, lakes, and rivers. When salmon enter fresh water, they have stored nearly all of the energy necessary for upstream migration and reproduction. The magnitude of stored resources varies greatly and depends on the length of the upstream migration. For example, chum salmon in the Yukon river may spawn near the mouth or nearly 2,000 kilometers upriver.
• kelt Kelts are salmons which have spawned; most salmons spawn only once during their lifetime and die within a week after spawning; survived salmon migrate back to saltwater.

Liza Gross. Can Farmed and Wild Salmon Coexist? PLoS Biol. 2008 February; 6(2): e46. (Image of Atlantic salmon: United States Fish and Wildlife Service)

 

Fink RD. It's elementary: Science Buddies bring biology to life. PLoS Biol. 2009 Aug;7(8) (Atlantic salmon larva reared in an elementary classroom as part of a restoration project in Massachusetts. Photo: Haruka Fujimaki)

 

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References

• Darimont CT, Paquet PC, Reimchen TE. Spawning salmon disrupt trophic coupling between wolves and ungulate prey in coastal British Columbia. BMC Ecol. 2008 Sep 2;8:14. PMID: 18764930
• Ford JS, Myers RA. A global assessment of salmon aquaculture impacts on wild salmonids. PLoS Biol. 2008 Feb;6(2):e33. PMID: 18271629
• SCOTT M et al. Pacific Salmon in Aquatic and Terrestrial Ecosystems. PLoS Biol. 2008 Feb;6(2):e33. (.pdf)
• Major topic "salmon": free full-text articles in PubMed