Salmon

• 1. Introduction

  ›

  Salmon from central Idaho, Chinook and sockeye alike, travel over 900 miles from the Pacific and climb nearly 7,000 feet to spawn. Each of these fish is going home, to the freshwater stream where it hatched before heading out to live in the ocean. For many of them, arrival is also the end. How does a fish find a stream it left behind? Why does a journey that costly so often finish in death? What happens to a forest, a bear and a river when the fish arrive, or fail to? And how did a fish that once dominated the Pacific become one that people raise in net cages at sea? To answer any of that, it helps to know what counts as a salmon at all, because the name is looser than it looks.

  12336

• 2. Names and Kin

  ›

  The Modern English word salmon descends from Anglo-Norman saumon and Middle English forms such as samoun and samon. Those trace back to the Latin salmō, which may have come from salire, meaning to leap. The silent l was a later addition, inserted to pull the spelling closer to its Latin root. An older word, lax, descended from the Proto-Indo-European *lakso-, now survives mostly in dialect. The origin of that ancient word for salmon even became part of the argument over where the Indo-European languages began.

  Salmon is a colloquial label, not a scientific one. The fish it covers belong to the family Salmonidae, alongside trout, char, grayling, whitefish, lenok and taimen. All of these are coldwater fish of subarctic and cooler temperate regions. Seven commercially important species fall into two genera. Salmo is native to the North Atlantic and holds the Atlantic salmon plus more than 40 species usually called trout. Oncorhynchus is native to the North Pacific and holds 12 recognised species, six of them Pacific salmon and the rest trout.

  The boundary is fuzzy. In Japan the masu salmon is considered a trout, a cherry trout, because masu is simply the Japanese word for trout. The Adriatic salmon and the Black Sea salmon are English names for fish outside the recognised seven. Meanwhile the steelhead and the sea trout live exactly the same migratory lives as salmon, from the same genera, yet neither is called a salmon.

  Some fish called salmon are not close relatives at all. The Australian salmon, the Hawaiian salmon and the Indian salmon belong to unrelated orders and earned the name through similar shape, behavior and niche. The Danube salmon, or huchen, is the true relative among the impostors. It is the largest permanent freshwater salmonid, reaches 52 kilograms, and is listed as endangered.

  The fossil record adds depth to the family tree. Eosalmo driftwoodensis, found in British Columbia, is the oldest known fish of the salmon subfamily. It shows that Pacific and Atlantic salmon had not yet split 40 million years ago. Fossils and mitochondrial DNA agree on the timing. The split came 10 to 20 million years ago, in the Miocene, long before the Quaternary glaciation began its cycle of advance and retreat.

  7892439

• 3. Seven Species, Many Ranges

  ›

  Chinook salmon are called king salmon or blackmouth salmon in the United States and spring salmon in British Columbia. A Chinook over 30 pounds is a tyee in British Columbia, and on the Columbia River the especially large ones were once nicknamed June hogs. This is the largest Pacific salmon, frequently longer than 6 feet, with a recorded maximum weight of 61.4 kilograms. Its range runs from the Mackenzie River and Kugluktuk in the central Canadian Arctic to the Central Californian coast.

  Chum salmon go by dog salmon or calico salmon in parts of the United States and keta in the Russian Far East. They have the widest range of any Pacific species. In the east they stretch from north of the Mackenzie River to south of the Sacramento River. In the west they reach from the Lena River in Siberia to the island of Kyūshū.

  Coho salmon are silver salmon to Americans. They fill the coastal waters of Alaska and British Columbia and reach south to Monterey Bay in Central California. Occasionally one turns up in the Mackenzie River. The masu salmon lives only in the western Pacific, in Japan, Korea and the Russian Far East. A landlocked subspecies, the Taiwanese or Formosan salmon, survives in central Taiwan's Chi Chia Wan Stream.

  Pink salmon are humpback salmon, or humpies, in Alaska. They are the smallest Pacific species, averaging 3.5 to 4.0 pounds, and they favor shorter coastal streams. In the west they range from the Lena River in Siberia to Korea. In the east they run from the Mackenzie River to northern California.

  Atlantic salmon spawn in northern rivers on both sides of the Atlantic. Some have given up the sea entirely. A landlocked form lives in lakes including Sebago, Onega, Ladoga, Saimaa, Vänern and Winnipesaukee. It is not a separate species. It evolved its freshwater-only life independently, and it keeps that life even where the ocean is within reach.

  Sockeye salmon, called red salmon in Alaska, rear in lakes. They range from Bathurst Inlet in the Canadian Arctic to the Klamath River in California, and from the Anadyr River in Siberia to northern Hokkaido. Most adult Pacific salmon hunt small fish, shrimp and squid, but sockeye filter plankton through their gill rakers. Kokanee, the landlocked form of sockeye, proved so appealing to anglers that they have been introduced across many places in the United States and Canada.

  2729303134

• 4. Gravel, Ocean, and Home

  ›

  Only about 10 percent of salmon eggs are estimated to survive long enough to become smolts. The eggs are laid in freshwater streams, typically at high latitudes, and hatch into alevin, also called sac fry. These quickly grow into parr, small fish with camouflaging vertical stripes. Parr stay in their birth stream for anywhere from six months to three years. Then they become smolts, which are bright silver and shed their scales at a touch.

  The smolt stage is a chemical transformation. Hormones including insulin-like growth factor I, cortisol and thyroid hormones adjust the gills and other organs so the fish can secrete salt. Migrating smolts spend part of the trip in brackish water while their bodies adapt to life in the sea. A few species skip this entirely and stay in fresh water for life.

  What salmon eat changes with each stage. Fry feed mostly on zooplankton. Fingerlings add insect larvae, microcrustaceans and worms. Parr turn predatory, taking tadpoles and small bait fishes, eating the eggs of other salmon, and even breaching the surface to snatch grasshoppers and dragonflies. At sea the adults behave like other mid-sized open-water fish, eating lanternfish, herrings, sand lances, mackerels, barracudina, krill, squid and polychaete worms.

  Depending on the species, salmon spend one to five years in the open ocean, slowly becoming sexually mature. Atlantic salmon stay between one and four years. In Canada, Britain and Ireland, an Atlantic salmon that returns after just one year at sea is called a grilse. Grilse can slip in at spawning time unnoticed by the large males and release their own sperm over the eggs.

  Folklore says each fish returns to the exact stream where it hatched. Tracking studies have shown this to be mostly true. A share of every run strays into other river systems, and how big that share is depends on the species. The homing itself rests on olfactory memory, a remembered smell.

  Spawners change shape on the way. Some grow a hump or develop canine-like teeth, and males may grow a kype, a pronounced hook in the jaw. The silvery blue of a fresh-run fish darkens. On arrival the female beats her tail to create a low-pressure zone. That lifts the gravel and sends it downstream, leaving a shallow depression called a redd. One redd may hold 5,000 eggs spread across 30 square feet. The eggs range from orange to red, and the male deposits milt over them. The female covers them by stirring gravel at the upstream edge. She may dig as many as seven redds before her eggs run out.

  Afterward the body fails quickly. In every species of Pacific salmon, the adults die within a few days or weeks of spawning, a trait called semelparity. Between 2 and 4 percent of Atlantic salmon kelts, the spent fish, survive to spawn again, and all of them are females. Even in species that can spawn more than once, post-spawning mortality may reach 40 to 50 percent. A surge of corticosteroids drives this rapid decline, known as phenoptosis, or programmed aging.

  The record of all this is written in an earbone called the otolith. It forms a ring for each year of growth. Freshwater years show as crowded rings and sea years as widely spaced ones. Spawning appears as heavy erosion, as body mass turns into eggs and milt. Eggs need cool, well-flowing water with enough oxygen, and silt, warm water, lost stream cover and reduced flows all raise early mortality. Estuaries and their wetlands serve as nurseries, filtering silt and pollutants while offering food and hiding places before the open ocean.

  23363739

• 5. Feeding the Forest

  ›

  Grizzly bears throw away up to half of the salmon they catch. Before hibernation they favor the energy-rich roe and brain over the flesh, and they drag fish onto dry land to eat. The leftovers, along with urine and feces, can reach densities of 4000 kilograms per hectare. They supply as much as 24 percent of the nitrogen available to nearby woodland. Spruce foliage up to 500 meters from a salmon stream has been found to contain nitrogen that came from the fished salmon.

  In the Pacific Northwest and Alaska, salmon are keystone species. Their migrations carry nitrogen, sulfur, carbon and phosphorus from the ocean into inland waters. Ospreys, bears and otters move some of it onto land. Nearly all Pacific salmon that reach the headwaters die there. Their bodies settle over the gravel and enrich streams that would otherwise hold little biomass.

  Beavers help in return. The Treaty of 1818 gave U.S. citizens access to the Columbia catchment. In the years that followed, the Hudson's Bay Company told its trappers to strip furbearers from the area, hoping to make it unattractive to American fur traders. With beavers gone from large parts of the river system, salmon runs plummeted, even without many of the usual causes of decline. Beaver dams slow the flushing of nutrients and create deeper pools where young fish dodge birds. They also form slow water where juveniles spend food on growth instead of fighting currents. In tidal marshes, dams under 2 feet high hold water at low tide and give juveniles a refuge from larger fish.

  Lampreys play a quieter role. Rivers that lose their anadromous lampreys also see salmon suffer. Lampreys die after spawning and release nutrients, and they clean river gravel as they spawn. Their larvae, called ammocoetes, are fattier and oilier than young salmon, so predators are assumed to prefer them. Seals and sea lions favor adult lampreys, eating 30 of them for every salmon, which lets more adult salmon reach the spawning rivers.

  Parasites complicate the picture. Canadian biologist Dorothy Kieser describes Henneguya salminicola, a parasite recorded in salmon returning to Haida Gwaii. The fish wall it off in cysts of milky fluid. Work at the Pacific Biological Station in Nanaimo in the mid-1980s found that coho were most heavily infected, followed by sockeye, chinook, chum and pink. The parasite does not seem to stop infected fish from spawning, and it is harmless to people.

  Underwater pile driving poses another hazard. A study led by Dr. Halvorsen concluded that fish risk injury when the cumulative sound exposure level exceeds 210 dB relative to 1 μPa2 s. Sea lice are deadlier. These ectoparasites feed on mucus, blood and skin, and crowded open-net salmon farms can build up huge concentrations of them. Small, thin-skinned juveniles migrating past those farms are highly vulnerable. On the Pacific coast of Canada, louse-induced mortality of pink salmon in some regions is commonly over 80 percent.

  4445485255

• 6. Nets and Hatcheries

  ›

  Since 1990 the wild salmon catch reported to the FAO has hovered around one million tonnes a year. Over the same period farmed salmon grew from about 0.6 million tonnes to well over two million. Nearly all captured wild salmon are Pacific salmon. The wild Atlantic catch has always been small and kept falling, with only 2,500 tonnes reported in 2011. About half of all farmed salmon, by contrast, are Atlantic.

  Sport fishing and commercial fishing compete for the same fish. Commercial netting in estuaries and coastal waters is often restricted so enough salmon reach their natal rivers. On parts of the North American West Coast, sport fishing has completely replaced inshore commercial fishing. The economics explain why. A fish caught by an angler can be worth several times what it fetches as seafood.

  Salmon farming brings in roughly US$10 billion a year. Norway is the world's largest producer, followed by Chile, with Scotland, Canada and the Faroe Islands also significant. The industry supplies most of the salmon eaten in the United States and Europe. Salmon are carnivores, so farms depend on wild forage fish. It takes 2 to 4 kilograms of wild-caught fish, by dry weight, to produce one kilogram of farmed salmon. That demand grows while 75 percent of the world's monitored fisheries are already near or past their maximum sustainable yield. Open-net cages are cheap to run but let disease and sea lice reach wild stocks.

  Feed for farmed salmon includes the carotenoids astaxanthin and canthaxanthin, which match the flesh color to that of wild fish. Wild salmon get astaxanthin from shellfish and krill. Researchers are testing alternatives to wild-caught feed. Soy-based feed may be gentler on the farm's local environment, but growing soybeans carries a high environmental cost and lowers omega-3 content. A yeast-based coproduct of bioethanol production can give equal and sometimes better growth. Seaweed supplies minerals, vitamins and dietary fiber, and in the best case could remove the need for land, fresh water or fertilizer.

  Hatchery ranching raises young salmon and releases them to rivers. It was common in Sweden before the Norwegians developed salmon farming. Because anyone can catch the returning fish, private companies struggle to profit from it. Public authorities and nonprofits such as the Cook Inlet Aquaculture Association run most of it. Its drawbacks include genetic dilution of wild stocks, and many jurisdictions now prefer harvest controls and habitat protection. In Alaska, ocean ranching releases young salmon far from any wild stream so that fishermen can catch them on their return. Spawning channels, artificial streams with gravel bottoms, offer a third route. They avoid floods that wash out natural redds and, unlike hatcheries, need no preventive chemicals against disease.

  2668707274

• 7. Counting the Survivors

  ›

  Theodore Roosevelt told Congress in his 1908 State of the Union address that the Columbia River salmon fisheries were a fraction of what they had been twenty-five years before. He blamed a struggle between Oregon and Washington, whose legislatures could not agree on joint protection. He also blamed the quarrel between gill-net fishermen and the owners of fishing wheels upriver. He predicted that in four years the fisheries would amount to nothing.

  Physical barriers did their own damage. In 1914 a slide caused by the Canadian Pacific Railway at Hells Gate affected the Fraser River salmon, and the 1917 catch was one quarter of the 1913 catch. The Chief Joseph Dam, completed in 1955, completely blocks salmon migration into the upper Columbia River system. Baseline data are almost impossible to rebuild from inconsistent records. Even so, Pacific salmon today number less than 1-3 percent of what they were when Lewis and Clark arrived.

  The present picture varies by place. Alaska's stocks remain abundant, and catches have risen since the state began imposing limits in 1972. Major sustainable fisheries operate near the Kenai River, the Copper River and Bristol Bay. Farming Pacific salmon is outlawed in the U.S. Exclusive Economic Zone, though a large network of publicly funded hatcheries exists. In Canada, returning Skeena River salmon support commercial, subsistence and recreational fisheries inland for hundreds of miles.

  Washington's record is mixed. Of 435 wild stocks of salmon and steelhead, 187 were classified as healthy. Another 113 had unknown status, 122 were depressed, 12 were critical and one was extinct. California's commercial fisheries have been severely curtailed or closed because of critically low returns on the Klamath and Sacramento rivers. The Atlantic is troubled too, especially the populations that spawn in western Europe and eastern Canada.

  Salmon have also been moved. In the late 1960s Michigan planted coho in the Great Lakes to control the growing population of non-native alewife. Chinook, Atlantic and coho are now stocked in all of the Great Lakes, producing a thriving sport fishery without self-sustaining runs. Wild, self-sustaining Pacific salmon populations have taken hold in New Zealand, Chile and Argentina. Anglers prize them there, and others worry about displaced native fish.

  In 2020 researchers reported that four wild Pacific species, Chinook, chum, coho and sockeye, had been shrinking in size for 30 years. The suspected causes are climate change and competition with growing numbers of pink and hatchery salmon.

  7577838676

• 8. Food, Ritual, and Myth

  ›

  Roughly 99 percent of the Atlantic salmon on the world market are farmed, while more than 80 percent of Pacific salmon are wild-caught. Salmon is an oily fish valued for protein, omega-3 fatty acids and vitamin D. Its cholesterol ranges from 23 to 214 milligrams per 100 grams depending on species. Reports in the journal Science noted that farmed salmon may carry high dioxin levels, and PCB levels up to eight times those of wild fish. Still, a 2006 study in the Journal of the American Medical Association concluded that the benefits of eating even farmed salmon outweigh the risks.

  The orange to red flesh comes from carotenoid pigments, mainly astaxanthin, though white-fleshed wild salmon do occur. Canned salmon in the United States is usually wild Pacific catch and traditionally includes harmless skin and calcium-rich bone. Smoked salmon may be hot- or cold-smoked, and lox can mean cold-smoked salmon or salmon cured in brine, also called gravlax. Raw flesh may carry Anisakis nematodes, which cause anisakiasis. Before refrigeration, the Japanese did not eat raw salmon, and salmon and its roe have only recently entered sashimi and sushi.

  For the Indigenous peoples of the Pacific Northwest Coast, salmon is a vital food and far more. Archaeologists traced the importance of salmon to coastal dwellers as far back as 5,000 years, after finding remnants of the Nisqually tribe. People used the whole fish, making glue from the bladder, toys from the bones, and clothing and shoes from the skin. The original salmon ceremony had three parts: welcoming the first catch, cooking it, and returning the bones to the sea. The bones went back so that other salmon would willingly give their lives to the village. The Yurok avoided taking the first fish swimming upriver in summer, and fishing began only once they confirmed the run had returned in abundance.

  On Haida Gwaii, the Haida call salmon tsiin and prepare it by smoking, baking, frying and making soup. Logging and development have destroyed much habitat, leaving fish close to endangered and limiting catches, which in turn affects family diets and feasts. Across British Columbia, a 2003 report for the Ministry of Agriculture and Food counted 595 First Nation-owned and operated commercial vessels. First Nations members owned 564 of them. Even so, employment in the industry had fallen by 50 percent over the previous decade, leaving 8,142 registered commercial fishermen. Black bears also depend on the fish, and the leftovers they leave feed the forest, which returns clean water and gravel to the salmon.

  Celtic tradition gave salmon a role as keepers of wisdom. In Irish folklore, fishermen linked salmon with fairies and thought it unlucky to say their name. In The Boyhood Deeds of Fionn, the poet Finn Eces hunts the Salmon of Knowledge for seven years. When he finally catches it, his pupil Fionn mac Cumhaill burns a thumb on the cooking fish. Fionn puts the thumb in his mouth and gains the wisdom himself. In the Welsh tale Culhwch and Olwen, the Salmon of Llyn Llyw is the oldest animal in Britain. It carries Cai and Bedwyr to the walls of Mabon's prison in Gloucester.

  Norse myth explains the salmon's tapered tail. After Loki tricked the blind god Höðr into killing his brother Baldr, Loki turned into a salmon and fled into a river. When the gods held out a net, he tried to leap it, but Thor grabbed him by the tail. Salmon are likewise central to the spiritual and cultural life of Pacific coast peoples. The Haida, the Coast Salish and the Nuu-chah-nulth in British Columbia all hold the fish at the center of their traditions.

  90932399100