by Craig Weatherby
Given the stresses on wild stocks, we hope that fish farming becomes a truly sustainable source of health-enhancing protein for billions of people who need one pretty badly.
Intuitively, it seems a good idea… the more fish grown in pens, the fewer need be taken from overfished wild stocks in the sea.
Writing in the June 29, 2000 issue of the leading journal Nature, Stanford University economist Rosamond Naylor and biologist Harold Mooney reported that, “…on balance, global aquaculture still adds to world fish supplies” (Shwartz M 2000).
But as Naylor and Mooney wrote, the rapid rise in aquaculture production “…is a mixed blessing, however, for the sustainability of ocean fisheries."
Onshore farms can be sustainable operations, but coastal shrimp and salmon farms have taken a toll.
Shrimp farms continue to devastate coastal mangrove forests, which serve as key fish breeding grounds… while salmon farms nearly wiped out wild Atlantic salmon and generate ongoing disease risks to wild stocks.
Just last month, geophysicist Neil Frazer, PhD of the Hawaii at Manoa published a paper in the journal Conservation Biology, in which he demonstrated how farming of fish in ocean cages is fundamentally harmful to wild fish (Frazer LN 2008).
In short, he uses existing data on disease transmission to calculate that higher density of fish promotes infection, and infection lowers the fitness of the fish.
His calculations show that even if lice levels on farm fish are controlled by medication, local wild fish will still decline.
Also, Frazer calculated a critical stocking level of farmed fish, above which local wild fish decline to extinction. He concludes that growing farm fish in sea cages can't save wild fish, but it can easily destroy them:
“Declines of wild fish can be reduced by short growing cycles for farm fish, medicating farm fish, and keeping farm stocking levels low. Declines can be avoided only by ensuring that wild fish do not share water with farmed fish, either by locating sea cages very far from wild fish or through the use of closed-containment aquaculture systems. These principles are likely to govern any aquaculture system where cage-protected farm hosts and… wild hosts have a common parasite with a direct life cycle” (Frazer LN 12/2008).
In an earlier 2008 paper, Frazer noted, drily, that the Canadian researchers who’d published strong evidence that that lice from salmon farms could kill off major wild Pink salmon runs in British Columbia “… probably underestimated [lice] larvae production by the salmon farm” (Frazer LN 10/2008).
And salmon farms devour massive loads of the small prey fish needed by wild salmon and other large fish … which explains why Naylor and Mooney warn that the growing demand for farm-raised salmon, shrimp and other commercially valuable species actually threatens the world's supply of fish.
The “underlying paradox,” they say, is that “…aquaculture is a possible solution—but also a contributing factor—to the collapse of fisheries stocks around the world” (Shwartz M 2000).
Nothing much has changed since Naylor and Mooney penned their plea for highly precautionary farm-regulation policies… despite some desultory moves to reduce the amounts of fish meal and oil in farmed salmon feed.
Now, a report from colleagues at Stanford raises new questions about sustainable siting and design of salmon farms... if true sustainability is even possible on offshore salmon farms.
Where does the waste go? Study throws cold water on industry assurances
In addition to possible pressure on wild stocks, marine aquaculture can have some nasty side effects, especially when the pens are set near sensitive coastal environments, like most industrial salmon farms are.
Fish penned together consume massive amounts of commercial feed, some of which drifts off uneaten in the currents. And the crowded fish, naturally, defecate and urinate by the tens of thousands, creating a septic waste stream.
The wastes can carry disease, causing damage directly to wild stocks. Or the phosphate and nitrates in the mix may feed an algae bloom that sucks the oxygen from the water, leaving it uninhabitable… as in Chesapeake Bay and the Gulf of Mexico, where fertilizer runoff made huge dead zones incapable of supporting the marine food chain.
It has been widely assumed that the effluent from pens would be diluted to harmless concentrations if the pens were kept a reasonable distance from shore.
But early results from a new Stanford University computer simulation, based on sophisticated fluid dynamics, show that fish farm waste will travel farther and in higher concentrations than had been generally assumed.
According to civil and environmental engineer Jeffrey Koseff, co-director of Stanford's Woods Institute for the Environment, “What we've basically debunked is the old adage that ‘The solution to pollution is dilution.' It's a lot more complicated” (Stober D 2009).
The computer modeling - done with new Stanford software that goes by the acronym SUNTANS - created a virtual coastal marine area resembling California's Monterey Bay.
Previous software could not accurately predict where the concentrated effluent from fish pens would end up, and the Stanford team say it should not be used—as it already has, many times—when state or federal regulators consider approving locations for fish farms.
Existing software models attempt to describe the drift of effluent from sewage outfall pipes, even though the substances and situations are different from fish farms (Sewage outflow, for example, is often warmer than the ocean water).
The fine details of modeling the flow of dissolved fish poop from a submerged cage are not as simple as they may seem. Many factors come into play, such as the design of the cage, how much of the current flows through it, and how much goes around, whether moving water swirl into eddies at the edges of the pen … even the effects of the rotation of the earth on the waste plume.
The fish farmer would prefer that currents flush out his pens frequently, but as those currents take out the garbage they might unfortunately deliver it to a mangrove ecosystem or a public beach. On the other hand, insufficient flow through the pen can create a “dead zone” on the ocean floor as the fecal matter and uneaten food pile up beneath the fish.
Stanford scientist Oliver Fringer is designing the software so that it can be used to assess any site where sufficient digital mapping of the area already exists.
And Stanford oceans expert Rosamond Naylor says that SUNTANS comes along just as federal and local officials begin spelling the details of new health and environmental regulations for offshore fish pens.
Dramatic success in the world of fish farming may breed new concerns. “Aquaculture is at a critical juncture,” Naylor warned in 2006. “The technology for ocean farming has come far enough to expand into a whole range of new species-cod, tuna, and halibut. It will be very lucrative, but potentially damaging to the environment.”
New plan would allow pens further offshore
A plan proposed in 2005 by the Bush administration would allow huge, floating fish-farm pens access to federal waters out to 200 miles.
The idea, if approved by Congress as expected, would be to lease sections of the ocean—and perhaps also abandoned oil platforms—to fish companies for 10 years at a time.
The United States imports 80 percent of the seafood it consumes, creating a seven-billion-dollar annual trade deficit… larger than any other natural resource except oil. The idea is to expand the U.S. aquaculture industry fivefold, to five billion dollars, and recapture some of that business.
While pens sited far offshore may be relatively more benign for the environment, they do little to address concerns that the amount of fish required to raise farmed fish could result in a net loss of fish due to disappearance of nutritionally superior wild fish.
(Farmed fish are typically fed a mix of fish meal, fish oil, and grain… this dramatically raises their levels of pro-inflammatory omega-6 fats, which compete in the body with anti-inflammatory omega-3s. See “Farmed Fish Possess Unhealthful Fat Profiles.”
Writing in the October, 2003 issue of Environment magazine, a Stanford University research team found that, farmed salmon represents one of the fastest-growing and most lucrative segments of the global aquaculture industry, and that the impact has been particularly devastating in Alaska, where 10 percent of the workforce is employed in some aspect of the salmon fishing industry.
We can attest to the truth of the statement by Stanford professor Rosamond Naylor: “Wild salmon capture historically has played an important economic role by providing employment and incomes to a vast number of Native American and non-native communities along the coast.”
- Frazer LN. Sea-Cage Aquaculture, Sea Lice, and Declines of Wild Fish. Conserv Biol. 2008 Dec 10. [Epub ahead of print]
- Frazer LN. Sea-lice infection models for fishes. J Math Biol. 2008 Oct;57(4):595-611. Epub 2008 May 7.
- Rogers P. Aquaculture specialist Rosamond Naylor explores whether fish farms can sustainably meet the growing world demand. Stanford Magazine, March 20, 2006. Accessed online February 21, 2009 at http://cesp.stanford.edu/news/aquaculture_specialist_rosamond_naylor_explores_whether_fish_farms_can_sustainably_meet_the_growing_world_demand_20060320/
- Shwartz M. Do fish farms really add to the world's supply of fish? June 27, 2000. Accessed online February 21, 2009 at http://news-service.stanford.edu/pr/00/fishfarms628.html
- Stober D. When fish farms are built along the coast, where does the waste go? February 15, 2009 Accessed online February 21, 2009 at http://www.eurekalert.org/pub_releases/2009-02/su-wff021109.php
- The University of Hawai?i (UH). Ocean Fish Farming Harms Wild Fish, SOEST Study Says. December 12, 2008. Accessed online February 21, 2009 at http://www.hawaii.edu/cgi-bin/uhnews?20081212151031