You would think that farming fish is a good way to protect wild fish. This Science Update looks at a study that shows that salmon farms may be killing wild salmon instead of saving them.
How raising salmon can kill salmon. I'm Bob Hirshon and this is Science Update.
A salmon farm can indirectly kill young wild salmon within a thirty-five mile radius. This according to a study of over fourteen thousand fish, led by Ph.D. student Martin Krkosek at the University of Alberta in Canada.
He explains that salmon farms are teeming with sea lice: a surface parasite that's relatively harmless to adult salmon, but deadly to juveniles.
These fish are only about an inch long. They don't have any protective scales, and all it takes is one or two lice to kill them.
In the wild, juveniles rarely get sea lice, because they grow up far away from adult carriers. But Krkosek found that fish farms along juvenile migration routes can infect and kill up to 95 percent of the young fish that pass by. As a result, he says that farming appears to be depleting the wild salmon population, rather than saving it.
I'm Bob Hirshon for AAAS, the science society.
Making Sense of the Research
More and more of the fish and seafood you buy in the grocery store, or order in restaurants, comes from fish farms. On the surface, fish farms sound great: they provide cheaper fish without directly depleting the shrinking wild fish populations.
But as you heard in this report, it's not necessarily that simple. In this case, Krkosek and his colleagues found that farmed salmon could indirectly kill wild salmon, if the farms are within thirty-five miles of the juveniles' migration routes. There are over 280 salmon farms in Canada (compared with only nine in the U.S.), so there's no shortage of opportunity for this to happen. Normally, in nature, juveniles hatch in coastal streams and rivers, then migrate up to thousands of miles out to the open ocean. (Their parents would have left or died months ago.) Therefore, salmon spend the early parts of their lives completely apart from adults. But in salmon farms, adults and juveniles share the same relatively small space, often separated from open waters only by net.
Krkosek's team netted and studied fish at various points along three different salmon migration routes. They found sea lice infections on many of the salmon. Salmon with more lice were more likely to die, but in some cases just one louse was enough to kill a fish. Furthermore, they found that the young salmon picked up the sea lice as they passed near salmon farms; that the more salmon farms they passed, the higher the infection rate; and that infections in the wild salmon increased as the migration season went on, which is exactly what happens in salmon farms.
Taken together, the evidence strongly suggests that salmon farms kill wild salmon. There are potential solutions to the problem: for example, cutting off salmon farms from the open waters, or moving the farms far from migration routes. Unfortunately, both solutions are expensive and logistically difficult. But if the problem persists, farmed salmon may eventually become the only salmon around.
Now try and answer these questions:
- What does it mean to say that salmon farms kill wild salmon?
- How did Krkosek's team demonstrate this?
- Overfishing has nearly destroyed many wild fish populations, yet demand for fish and seafood continues to increase. Do you think fish farms are a necessary part of the solution? Why or why not?
- In what ways do economic factors affect this situation?
You may want to check out the October 23, 2006 Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: cycles in the Earth's orbit and tilt may cause extinctions, what got the Oracle of Delphi high, why farming salmon hurts their wild cousins, the masculine face of compulsive shopping, and the health benefits of smoking bans.
The National Geographic News articles Sea Trout Loss Linked to Salmon Farm Parasite, Salmon Farm Escapees Threaten Wild Stocks, and Environmentalists Fight Plans to Farm Cod in Scotland highlight some of the controversial elements of fish farming.