AQUACULTURE VS. NATIVE FISH STOCKS: WHO GETS TO EAT?

Wild fish stocks are not inexhaustible.  Just as agriculture has largely replaced market hunting, at least in the developed world, aquaculture will almost surely be needed to provide enough seafood to satisfy growing demand.

Yet agriculture didn’t come without costs.  The vast areas cleared to provide croplands and ranches destroyed almost all of the prairie ecosystem, which once stretched from the banks of the Mississippi River to the foothills of the Rocky Mountains.  Millions of bison no longer roam the Great Plains.  Grassland birds are, on the whole, in deep decline.  Prairie dogs, ecosystem engineers that create “towns” that might cover many square miles, have been extensively poisoned by ranchers who see them as competitors for grass needed to raise cattle; as a result, their networks of complex burrows, which serve as homes for an array of other animals, have been lost in much of the West. 

We would be naïve to believe that a growing aquaculture industry won’t cause similar harm to marine and coastal habitats.  While the ocean may be vast, the most productive sections of coast—our estuaries, marshes, coral reefs, and hard bottom—are a very small and vulnerable part of the whole, and can easily harmed by the infrastructure needed to support a burgeoning aquaculture industry. 

Apart from changes to the physical environment, we can expect changes to ecosystems and food webs, as aquaculture operations introduce alien species to coastal waters, increase nutrient loads in sheltered bays, and concentrate parasites harmful to wild fish in the vicinity of fish pens.

One of the biggest questions is what the penned fish, which are farmed in concentrations far denser than would exist naturally, are going to eat, and just where that food will come from.  Should there not be enough forage available to support both a growing and increasingly powerful aquaculture industry and wild fish stocks, which will prevail, and which will be forced to make do with less?

The answer might not be good news for the wild stocks.

A study was done in Finland, where scientists began looking for reasons why Atlantic salmon in the River Teno seemed to be getting smaller and spawning at younger ages.

Typically, when that sort of thing happens, fishing is the most likely cause, as high harvest levels limit fish growth and favors those that spawn at younger ages.  

While fishing probably made some contribution to the changes in River Tano salmon, overfishing was not an issue; instead, fish size is probaby affected by the selectivity of the nets most used by commercial fishermen.  The researchers chose to dig deeper into why the salmon are shrinking.  An article on the phys.org website quotes one of the scientists, Dr. Yann Czorlich, who described what they did:

“The previous research couldn’t tell us what environmental or human influences might be linked with the evolutionary changes.  To understand this, we needed to link the yearly changes in the salmon DNA variation with environmental and human-linked factors.  We gathered literally millions of data-points about factors, including yearly water temperature, salmon fishing effort, and commercial fisheries catches of the fish salmon eat in the ocean, and compared them with our data on DNA changes in our 40 year time series.”

The data suggested that the declining size of the River Tano salmon might be linked to high commercial landings of capelin, a small, oily fish that is important forage for wild salmon, but is also heavily fished to provide feed for aquaculture operations.  The article notes that, globally, 18 million tons of capelin and other forage species are removed from the ocean each year for use as animal feed.

That’s a number that will only get larger as aquaculture operations expand.

And it’s not only fish food that is being used to support aquaculture operations.  An article published last Tuesday in the journal PLOS Sustainability and Transformation, titled “Maximising sustainable nutrient production from coupled fisheries-aquaculture systems,” notes that

“Aquaculture expansion is expected to meet growing demand for sustainable animal-source foods.  Yet marine-fed species already require millions of tonnes of wild-caught fish for feed, over 90% of which are nutritious food-grade species.”

Using fish that could be eaten by people to feed aquacultured fish instead, so that people can then eat the aquacultured product, is hardly an efficient way to support increasing demand for seafood.  The researchers, which focused on the Scots salmon aquaculture industry, found that only between 1% and 49% of the “essential dietary minerals and fatty acids available in wild fish are found in farmed salmon,” and concluded that

“reducing marine feeds in salmon production and allocating wild-caught feed for human consumption could produce more nutritious seafood and leave 66-82% of feed fish in the sea.  Using global data on marine-fed aquaculture production, we show that removing wild-caught fish from salmonid production could leave 3.7 [million metric tons] fish in the sea while increasing seafood production by 6.1 [million metric tons].”

In other words, limiting the use of forage fish as aquaculture feed, and diverting a portion of those forage fish for human consumption, would benefit both people and the environment, which is as big a win/win as we are ever likely to see. 

Of course, things are never quite that easy.

While the researchers conclude that

“marine-fed farmed salmon is an inefficient way to produce nutritious seafood,”

it is nonetheless true that a lot of people like to buy farmed salmon, in part because of its taste, but also because it has been heavily promoted as a healthy food choice.  The fish currently being used for salmon feed include herring and related species, such as anchovies and sardines, which are not nearly as popular as table fare, particularly in the United States, where people are used to being able to buy a variety of wild seafood.

Yet that probably doesn’t justify fishing down wild forage fish stocks, perhaps to the detriment of wild species, in order to support fish farms.  The purpose of aquaculture, like agriculture, is to provide a reliable source of nutritious food, not to provide an endless variety of food options.

A few years ago, the New York Times published an article describing a fantasy Thanksgiving menu that Mark Twain wrote while visiting Italy.  As the Times observed,

“he surrounded the traditional holiday dishes with roast wild turkey, frogs and woodcock.

“Along with hot biscuits, broiled chicken and stewed tomatoes, Twain wanted turtle soup, possum and canvasback ducks fattened by Chesapeake Bay wild celery.  In Twain’s day, New York City markets still sold raccoons, a profusion of wild ducks and bear.”

These days, New York markets no longer routinely carry frogs (although a few do), woodcock, possums, raccoons, or bear, nor do they carry other truly wild game.  Instead, markets carry the meat of creatures most amenable to efficient, high-intensity farming:  chicken, beef, pork, lamb, and turkey, with some duck, goose, and goat occasionally thrown in.

In order to provide adequate feed for the future, we should not allow aquaculture to deprive natural ecosystems of many of their forage fish in order to provide a host of different seafood offerings, but instead to concentrate on species that can be efficiently and sustainably farmed:  tilapia, catfish, carp, oysters, mussels and such—perhaps even kelp—in order to maximize human nutrition while minimizing ecosystem damage.

Only thus can human nutrition be provided in a sustainable manner.