Aquaculture of salmonids
However, the concept of "wild" salmon as used by the Alaska Seafood Marketing Institute includes stock enhancement fish produced in hatcheries that have historically been considered ocean ranching.
[8] When they are 12 to 18 months old, the smolt (juvenile salmon) are transferred to floating sea cages or net pens anchored in sheltered bays or fjords along a coast.
However, exposing fish to wild parasites and pathogens using uncontrolled water supplies, combined with the high cost of spawning channels, makes this technology unsuitable for salmon aquaculture businesses.
[9][14] In contrast to closed or recirculating systems, the open net cages of salmonid farming lower production costs, but provide no effective barrier to the discharge of wastes, parasites, and disease into the surrounding coastal waters.
An emerging wave in aquaculture is applying the same farming methods used for salmonids to other carnivorous finfish species, such as cod, bluefin tuna, halibut, and snapper.
The resistance of organism growth on copper alloy nets also provides a cleaner and healthier environment for farmed fish to grow and thrive.
To obtain maximum quality, minimizing the level of stress is necessary in the live salmon until actually being electrically and percussively killed and the gills slit for bleeding.
Before killing, the fish are usually rendered unconscious in water saturated in carbon dioxide, although this practice is being phased out in some countries due to ethical and product quality concerns.
Harvesting and killing methods are designed to minimize scale loss, and avoid the fish releasing stress hormones, which negatively affect flesh quality.
In 1972, Gyrodactylus, a monogenean parasite, was introduced with live trout and salmon from Sweden (Baltic stocks are resistant to it) into government-operated hatcheries in Norway.
[44][45] Globally, salmon production fell around 9% in 2015, in large part due to acute outbreaks of sea lice in Scotland and Norway.
[49] In the mid 1980s to the 1990s, bacterial kidney disease (BKD) caused by Renibacterium salmoninarum heavily impacted Chinook hatcheries in Idaho.
Siting decisions are complicated by complex, politically driven permit problems in many countries that prevents optimal locations for the farms.
Huge volumes of uneaten feed and fish excrement pollute the seabed, while chemicals designed to fight sea lice find their way into the food chain.
[69] Sea lice, particularly Lepeophtheirus salmonis and various Caligus species, including C. clemensi and C. rogercresseyi, can cause deadly infestations of both farm-grown and wild salmon.
[42] Later that year, in reaction to the 2007 mathematical study mentioned above, Canadian federal fisheries scientists Kenneth Brooks and Simon Jones published a critique titled "Perspectives on Pink Salmon and Sea Lice: Scientific Evidence Fails to Support the Extinction Hypothesis "[77] The time since these studies has shown a general increase in abundance of Pink Salmon in the Broughton Archipelago.
And in relation to the 2007 Krkosek extinction theory: "the data was [sic] used selectively and conclusions do not match with recent observations of returning salmon".
The authors also note that initial studies had not investigated bacterial and viral causes for the event despite reports of bleeding at the base of the fins, a symptom often associated with infections, but not with sea lice exposure under laboratory conditions.
A company, Aqua Bounty Farms, has developed a modified Atlantic salmon which grows nearly twice as fast (yielding a fully grown fish at 16–18 months rather than 30), and is more disease resistant, and cold tolerant.
[16] This market shift at constant production appears an economic decision implying that the development of salmon aquaculture had no impact on forage fish harvest rates.
The WWF had originally identified what they called "seven key environmental and social impacts", characterised as: Recirculating aquaculture systems make it possible to farm salmon entirely on land, which as of 2019 is an ongoing initiative in the industry.
[96] In the United States, a major investor in the effort was Atlantic Sapphire, which plans to bring salmon raised in Florida to market in 2021.
[100] In their natal streams, Atlantic salmon are considered a prized recreational fish, pursued by avid fly anglers during its annual runs.
It is easy to handle, grows well in sea cages, commands a high market value, and adapts well to being farmed away from its native habitats.
[104] The risk of Atlantic Salmon becoming a legitimate invasive threat on the Pacific Coast of N. America is questionable in light of both Canadian and American governments deliberately introducing this species by the millions for a 100-year period starting in the 1900s.
Inland production of rainbow trout to supply domestic markets has increased strongly in countries such as Italy, France, Germany, Denmark, and Spain.
They also eat fish eggs and adult forms of terrestrial insects (typically ants, beetles, grasshoppers, and crickets) that fall into the water.
Smolt (young fish) from freshwater hatcheries are transferred to cages containing several thousand salmon, and remain there for the rest of their lives.
A site in Tekapo, fed by fast, cold waters from the Southern Alps, is the highest salmon farm in the world, 677 m (2,221 ft) above sea level.
[116] Lack of disease in wild populations and low stocking densities used in the cages means that New Zealand salmon farmers do not use antibiotics and chemicals that are often needed elsewhere.
