Fish Food: Wild and Farmed Salmon
Fish are a vital component of the human diet - nearly half the world’s population gets the majority of its protein from seafood. As the world population grows, and as more consumers recognize the environmental and health benefits of eating fish, the demand on fish stocks is increasing. Many species - perhaps 70% or more - have been fished to their sustainable limits or beyond. Because of increased demand and shrinking wild supply, the practice of fish farming is growing almost explosively. Proponents of fish farming say that the industry not only supplies an important food resource, it also benefits wild stocks by reducing fishing pressures. Many fishermen and environmentalists disagree, claiming that aquaculture can degrade the habitat, health, and genetic vigor of wild species.
In this activity, you will examine some of the benefits and drawbacks of aquaculture by comparing wild and farmed salmon. Salmon - a generic term applied to several Pacific and Atlantic species - are prized by consumers for both their taste and their high levels of protein and beneficial fish oils. Regular consumption of either wild or farmed salmon can lower the risk of heart disease. The wild salmon fishery is large and economically valuable, and salmon farming is the third largest component of the aquaculture industry. However, while salmon farming is booming, many populations of wild salmon are dwindling rapidly, under the pressures of over-fishing and environmental damage.
Instructions: Each of the facts listed below apply to wild or farmed salmon. Click anywhere on the image to align each statement with the correct puzzle box. When you have filled in both boxes, compare the environmental and nutritional characteristics of wild and farmed salmon, and then answer the questions that follow.
- Describe how aquaculture can harm the habitat around a fish farm.
Large numbers of fish are contained in a small area in fish farms. Their wastes, and any leftover food they don’t eat, will sink to the bottom below the cages and pens. This material can smother bottom life and disrupt the natural nutrient cycling, perhaps causing toxic algal blooms. Decomposition of large amounts of waste and algae can use up the oxygen in bottom sediments and waters and kill slow-moving organisms.
- What are the environmental benefits of fish farming?
Farmed fish are held in nearshore cages and so are easily harvested. Fishing techniques that can cause environmental damage, like bottom trawling, or that produce a large bycatch, are not necessary. If fish farming reduces the pressure on wild stocks, those populations may be able to rebound, which would help not just the fish but also the other species that feed on them.
- Suggest ways to minimize the negative environmental impacts of aquaculture.
If offshore fish farms were restricted to areas with strong currents, or if the size of the farms was restricted, the waste problem would be reduced. If cages are kept in good repair, escapes can be minimized. Perhaps the most effective way to protect the marine environment would be to move fish farms out of the sea, to pens and ponds built on land.
- Which is more likely to turn a profit, salmon fishing or salmon farming? Explain your answer.
Salmon farming is probably more profitable. Wild stocks are declining, so it may take more work to catch fewer fish. A salmon farmer can control the number and size of fish grown, and isn’t affected by regulations restricting when or how the fish are harvested.
- Farmed and wild salmon are both affected by parasites and diseases. In recent years, though, several populations of one of these groups have been devastated by infestations of sea lice picked up from the other type of salmon. Where do you think outbreaks of infectious diseases are most likely to begin? How would these conditions spread to the other category of salmon?
Diseases will break out more often in fish farms because large numbers of animals are kept in one place under crowded conditions. If sick fish escape their pens, or if wild fish swim past them on their way to or from their spawning grounds, they can become infected. If the diseases that develop on a fish farm are not endemic to the area, the local wild population may have little or no natural resistance.
- One type of salmon contains significantly higher levels of environmental pollutants like PCBs, dioxins, and pesticides than the other. Most scientists attribute this difference in contaminant levels to the different diets of wild and farmed salmon. Wild salmon eat a range of plants, shrimp, and smaller fish. Farmed raised salmon are fed high protein pellets made from concentrated fish and fish oils. Do wild or farmed salmon contain more toxins? How might the difference in diet cause this?
Farmed salmon have much higher levels of contaminants. Wild animals migrate far away from shore and spend several years far away from the pollutants that wash off the land. They also eat a more varied diet, composed of organisms lower on the food chain. Farmed salmon are fed a diet of other fish, and concentrating the oils and proteins into pellets would also concentrate any toxins they contain.
Critical ThinkingWhich is better for consumers, farmed or wild salmon? Justify your choice.
Scientists seek to understand and explain how the natural world works. Many of the questions raised in this endeavor have no absolute answers.
On a fish by fish comparison, wild salmon is healthier - it has more beneficial fish oils, less fat and contaminants, and none of the food dyes and antibiotics found in farmed animals.
But both types of salmon promote heart health. And farmed salmon is cheaper and available year round. Consumers won’t get any of the benefits of a diet rich in fish if they can’t find or afford the wild variety.
Wild salmon stocks are also declining rapidly even as consumer demand for seafood rises. Without farmed fish to supply large quantities of popular varieties like salmon, native stocks might soon be driven to extinction.