Crowded condition of farmed fish encourages parasitic sea lice.
Parasites attack young wild salmon as they return to the sea and are threatening the sustainability of wild stocks.
Wild Atlantic Salmon Stocks
Atlantic Salmon (Salmo salar) come into fresh water to spawn. The young travel down to the sea, and then spend a couple of years feeding in the ocean. The adult fish are genetically programmed to return to the river system of their birth, and the cycle continues. Since the 1970’s the number of adults returning to spawn has reduced by over 50%, and there are now thought to be less that four million wild salmon in the ocean.
Fish Farming Atlantic Salmon
The farming of Atlantic Salmon began in the 1970’s, initially in Norway and Scotland. Eggs are ‘stripped’ from adult salmon, hatched and raised in fresh water. When they are big enough they are put in cages, usually in estuaries, where they are fattened up for market. It is estimated that there are currently around 270 million farmed salmon (compared to 4 million wild!).
Effects of Fish Farming on Atlantic Salmon Stocks
- The crowded conditions of the farmed salmon in their cages are ideal for encouraging parasites (see ‘Sea Lice Affect Wild Salmon’ and ‘Sea Lice and Salmon’). Unfortunately wild salmon often need to swim past these fish farms to get to the open sea, and in doing so they can pick up heavy infestations of these parasites – enough to threaten their survival.
- Sometimes cages get damaged allowing farmed salmon to escape into the wild, and although this might initially appear to be a ‘good thing’, these escapees are genetically different from the truly wild fish, and their effect on the wild stock is detrimental.
(Watch the very impressive ‘National Geographic Multimedia Presentation’).
History of Salmon as Food
- As far back as 20,000 BC salmon were an important food. (A carving of a salmon has been found in a cave in the Vezere region of the Dordogne – France – of this date.) There is also evidence of salmon traps in the same river system dating to around 10,000 BC.
- More recently the site of Westminster Abbey in London is said to have been determined by the presence of salmon fishermen over a thousand years ago. (The fishermen believed they had ferried St.Peter across the Thames, and this superstition led to the building of first a chapel, and later an Abbey, where he was supposed to have been landed.)
- Even more recently salmon was so cheap and plentiful in London that mediaeval apprentices had it written into their agreements that they would not be fed salmon more than once a week.
Like oysters, salmon were once thought of as ‘food for the poor’, but have now become a luxury food.