Shrimp fountains don't grow on trees, you know—nor do Ahi Tuna steaks, Fish McBites, or fried calamari. But that hasn't stopped an increasingly affluent human population from annually demanding more and more seafood. As a result, an estimated 85 percent of the ocean's fish stocks are now either fully exploited or overfished. But an ancient form of aquatic farming, and current $60 billion-a-year industry, may hold the key to both protecting wild fish populations and your local sushi shop.
Conventional current fisheries are facing a crisis of supply, as any show on the History or Discovery channels can tell you (looking at you, Big Shrimpin'/Deadliest Catch/Swords/Wicked Tuna). Not only are fishermen pulling fewer fish out of the sea, the ones that are harvested are far smaller than those caught just a few decades ago. What's more, overly broad Area of Effect methods used to capture desired fish—long lines and trawl nets, for example—all too often ensnare and kill marine mammals and fish, known as by-catch, or damage delicate habitats. While many countries have enacted strict treaties and regulations dictating what, when, and how many fish can be gathered during a season, many fisheries are still treated, essentially, as non-renewable resources.
But that's changing with the help of aquaculture. This practice is the agricultural revolution to industrial fishing's hunter-gatherer method. Instead of sending out fleets of ships across the ocean in search of wild quarry, the fish are bred and raised in enclosed, human-controlled (or at least monitored) environments.
According to the Food and Agriculture Organization of the UN (FAO), aquaculture "is understood to mean the farming of aquatic organisms including fish, mollusks, crustaceans and aquatic plants. Farming implies some form of intervention in the rearing process to enhance production, such as regular stocking, feeding, protection from predators, etc." We're domesticating fish and doing a damn fine job of it with the annual production volume of farmed fish on the verge of surpassing wild-caught. The US aquaculture industry alone produces over a billion dollars worth of seafood annually. We didn't invent it though.
Aquaculture has been around since at least 6000 BC when the indigenous Gunditjmara people living near what's now Victoria, Australia began raising eels in a 39 square mile patch of volcanic floodplains controlled by channels and dams. The Chinese raised carp trapped in lakes by receding flood waters for food as far back as 2500 BC (and through their efforts, invented goldfish). The Romans bred fish in grand ponds, as did early Christian monasteries throughout Europe in the Middle Ages.
While dropping transportation costs and increasing speeds made moving fresh fish inland feasible and reduced the demand for aquaculture by the middle of the 19th century, research continued. Both experimental and commercial hatcheries opened throughout the US and Canada during that time, including the Woods Hole hatchery which operated from 1885 to the 1950s, and the Dildo Island fish hatchery in Newfoundland, which was the most advanced hatchery to date when it opened in 1889, producing and releasing 200 million cod per year back into the North Atlantic. Even aquatic plants like seaweed and kelp have been intentionally grown for harvest. Californians harvested and managed kelp supplies during WWI as they did other wartime resources.
These efforts were modest at best though, often more just a way to keep wild-caught fish until ready to eat rather than the fully-domesticated agricultural systems developed for cattle or chickens. In fact, only three percent of the roughly 443 maritime species raised in 2007 were domesticated before the start of the 20th Century and 106 of those species being domesticated only within the preceding decade.
Today, however, the US is the second largest seafood importer worldwide and one of its largest exporters. US aquaculture raises salmon, tilapia, striped bass, sturgeon, walleye, catfish and yellow perch as well as sport fish like rainbow trout and bait fish like minnows. Catfish is the largest US aquaculture sector, notching 40 percent of all sales. They're typically grown in large freshwater ponds throughout the Gulf Coast as are most of these other species, save for the salmon, which are grown in fresh water tanks then transferred to salt-water pens to mature. Crawfish, abalone, oysters, clams, mussels, even alligators and turtles are all produced in large aquaculture systems throughout the country. Aquatic plants destined for wetland restorations and algae like spirulina that's used for nutritional supplements and fish food are also regularly grown using aquaculture.
Worldwide, the four most-raised species are, in order: carp, salmon, tilapia and catfish. Tuna is not on that list due to the species' massive size, feed requirements, and the fact that nobody could entice them to get it on in captivity until 2009—fisheries in the Mediterranean used to have to net young blue fin at sea and drag them back to off-shore pens for maturing. While more efficient than conventional fishing, this method is not without drawbacks. Take Alaskan salmon, for example. As part of the state's hatchery program, artificially fertilized salmon roe is cultured in a hatchery and fed powdered fish meal until the juvenile salmon, or smolts, are big enough to move out to salt-water sea cages, which keep the salmon in and predators out. These huge pens can be up to 100 feet wide and hold 353,147 cubic feet of water as well as 90,000 fish. Once the fish are large enough to compete with wild salmon, they're released into the open ocean, returning to spawn at the hatchery in two to six years, depending on the type of salmon.
Many of these fresh water hatcheries are the "flow-through" variety, which need an intensive supply of running water to carry away waste—up to a 100 tons for every kilogram of smolts. The growing fish require a large amount of feed as well—feed typically made out of wild fish and offal. Three pounds of wild fish are required, on average, to produce a pound of farmed salmon (which is totally the opposite of what we're going for). What's more, the salt water pens do very little to keep waste, disease, and parasites from spreading from the salmon stock into the surrounding environment. And if the pen is situated in an area with insufficient water flow, toxic heavy metals will accumulate on the seafloor and wreak havoc on the local environment.
These toxins also build up in the salmon themselves at concentrations far higher than in their wild counterparts. A 2004 Cornell study found significant amounts of organochlorine contaminants in farmed salmon which, if ingested over long periods, could build up to dangerous levels for humans. Conversely, the same farmed salmon also possessed two to three times the amount of beneficial omega-3 acids than their wild cousins, so there's a trade-off. As Steven Schwager, Cornell associate professor of biological statistics and computational biology explains,
For a middle-aged guy who has had a coronary and doesn't want to have another one, the risks from pollutants are minor ones, and the omega-3 benefits him in a way that far outstrips the relatively minor risks of the pollutants. But for people who are young—and they're at risk of lifetime accumulation of pollutants that are carcinogenic—or pregnant women—with the risks of birth defects and IQ diminution and other kinds of damage to the fetus—those risks are great enough that they outweigh the benefits.
Farm-rasied tuna often have lower concentrations of mercury than their wild relatives thanks to their diets. While wild Tuna eat fish that eat plankton that absorb mercury from the atmosphere and rapidly build up conentrations of the metal, farmed tuna are fed a diet of terrestrial farming byproducts like grain and soy. Farm-raised tuna do absorb some mercury regardless of diet and are often found to have elevated PCB and dioxin levels thanks to the fact that their pens are located in the ocean.
In light of these issues, Recirculating aquaculture systems (RAS) have been invented. As their name implies, each hatchery cleans and reuses a set water supply in an indoor farm (think hydroponic fish). This system allows fisheries specific control over the hatchery environment without the need for a fresh water supply. Not only can an RAS be located, well, anywhere, it can produce fish year-round rather than seasonally. Other carnivorous fish like cod or tuna could theoretically be raised in this manner as well.
In addition, larger fish species such as Kamapchi, cousin to the Yellowtail Tuna, could soon be raised on the open ocean, towed about in huge pens by tender vessels so that waste is distributed over a much wider area and causes far less local environmental damage. Kampachi Farm, the ideological successor to Kona Blue Water Farms, which was founded in 2001 by a pair of marine biologists is doing just that.
"The overall goal of these efforts is to reduce mankind's footprint on the seas, by transitioning toward a more nurturing relationship with our seafood," said Neil Sims, the co-founder and co-CEO of Kampachi Farms, in a press statement. "The Kona Blue operation made some tremendous advances in marine fish production. We grew over 1 million pounds of Kona Kampachi per year at that site, with no measureable impact on the environment beyond the immediate net pen area."
Commercial shrimp farming, on the other hand, faces a genetic hurdle. More than 75 percent of the world's shrimp supply is produced in Asia, specifically Thailand and China. The other 25 percent is mostly from South America by way of Brazil. Just two species, Pacific white shrimp and the giant tiger prawns, constitute 80 percent of the shrimp raised commercially. Two humongous mono-cultures of shrimp grown in less than a half dozen countries could easily be devastated by an outbreak of viral, bacterial, or fungal disease just as Tropical Race 4 nearly obliterated the Cavendish banana. Oh wait, never mind, they already have been. Repeatedly. And considering that the US imports 80 percent of the shrimp it consumes every year, some $3.5 billion dollars worth, a mass die off of Vietnamese shrimp will be tough for the American public to swallow (or not).
To prevent the spread of disease within US aquaculture, the US Environmental Protection Agency (EPA), the National Oceanic and Atmospheric Administration Fisheries Program (NOAA), the U.S. Department of Agriculture (USDA), the U.S. Fish and Wildlife Service (USFWS), the U.S. Army Corps of Engineers (ACOE), and state environmental agencies collaboratively provide oversight and regulatory enforcement concerning water quality and environmental protection. The Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) is specifically charged overseeing the health of animals and plants.
So, while aquaculture isn't the ideal end-all solution to our demand for seafood, it is currently one of the best and one of the only ways to do so. Because it's not like we can go back to the unbridled industrial fishing practices of last century—there simply aren't enough fish in the sea.