By Asbjørn Bergheim*
Similar to other Pacific salmon species, Chinook salmon strains are native to rivers along the NW coast of America from California to Alaska and to Asian rivers from northern Japan to Kamchatka. This species is commonly named King salmon, not least because of its size; it is rapidly growing and adults range in size between 5 – 25 kg, but may even reach a weight of 40 – 50 kg! King salmon is the state fish of both Oregon and Alaska. According to a Canadian textbook, the commercial catch world record is 57 kg (www.wikipedia.org/wiki/Chinook-salmon). A main reason for the extraordinary size is a rather long stay in the sea where some individuals may spend up to eight years before returning to their original river. The Yukon River strain actually has the longest freshwater migration of any salmon with over 3,000 km from the river mouth to the spawning grounds. No wonder these spawners need extra fat reserves and energy to ascend the huge river!
Until the late 1980’s, the harvested volume of King salmon was all wild catches. The farming then expanded rapidly and has dominated the global harvest over the last 20 years. This is partly due to a sad decrease of wild caught King salmon. Canada used to be a major producer of King salmon before the year 2005 with a peak annual volume of around 20,000 tons in the early 1990’s. Today, the Canadian production is closed down and so is former farming of King salmon in Chile. The significant producer at present is New Zealand representing 15 – 20 thousand tons per year.
Chinook smolt are transferred to sea at an age of around 6 months and grown to harvest size of 2 – 4 kg after some 18 months in the cages. Thus, the hatchery stage and the consecutive grow-out principally follow the farming routine of other salmonids.
Salmon farming in New Zealand is a Southern Island activity where the dominating regions for cage farms are Marlborough Sounds and Stewart Island. There are also some on-growing farms in freshwater utilizing ponds/raceways and hydro canals (www.aquaculture.org.nz/industry/king-salmon). Only a handful of sites on the coast and in the sounds are considered suitable for salmon operations as a result of critical farm site selection. The site criteria strongly emphasize sufficient current velocity to ensure good water exchange in the cages and to minimize settling of wastes on the seabed. According to the national aquaculture organization, the farmers and regional councils are decreed to monitor the environmental conditions frequently on the farming sites. The farming of salmon must be performed in a sustainable manner and ensure the fish’s welfare.
Diseases known to cause big problems and losses particularly in Atlantic salmon farms in other parts of the world, such as infectious pancreatic disease, infectious salmon anaemia, etc. do not seem to affect New Zealand’s King salmon farms. The strict bio-security procedures at the farms and absence of any native salmon species are considered to be the major reasons for production without the use of vaccines and antibiotics.
According to Alan Duckworth, research scientist of Blue Ocean Institute, New Zealand’s fish farming “is better than it is in other countries” (www.starchefs.com/cook/features/new-zealand-king-salmon-salmon-farming). The company New Zealand King Salmon represents two-thirds of the country’s produced volume. Neither disease nor sea lice have ever infected the company’s salmon stock, which means that there has been no discharge of antibiotics to the marine environment from the cage farms. Another emphasized environmental benefit of the farming practice is that the fish are kept at low stocking density – “extremely low compared to international standards” says Katherine Bryar, senior consultant at this company.
The Global Aquaculture Performance Index (GAPI, www.gapi.ca) is a tool developed to provide information about the environmental costs and benefits of farmed marine finfish. Including all significant species and aquaculture nations, the performance of King salmon culture in New Zealand demonstrated one of the very highest scores. Out of 20 different finfish species, King salmon actually obtained the highest GAPI score of them all.
Dr. AsbjØrn Bergheim is a senior researcher in the Dept. of Marine Environment at the International Research Institute of Stavanger. His fields of interest within aquaculture are primarily water quality vs. technology and management in tanks, cages and ponds, among others.