Farming Fish in the Ocean

Caption NOAA National Centers for Coastal Ocean Science

Coastal net pens off the coast of Maine.

October is National Seafood Month and this week we're exploring aquaculture - also known as fish farming - through the lens of sustainability. Aquaculture has been around for centuries and, in some locations, has grown into an unsustainable industry. If, as predicted by the UN, we're going to increasingly turn to fish to meet the protein needs of our rapidly growing, global population, it's time to take a fresh look at how we can produce fish in a way that is safe, plentiful and less damaging to the environment.

You're going to read this statistic several times on Ecocentric this week, but it's an important one: about half of the seafood eaten in the world today is farmed. Despite grizzly fishermen and stormy seas pictured on frozen fish packages and restaurant menus, chances are good that the fish you eat comes from a less-poetic cage in a bay, an artificial pond or a shellfish-heavy rope dangling just offshore. In some cases that's a good thing, especially since some types of aquaculture can be sustainable. But there are also serious ecological and health impacts that we all need to better understand.

Americans have an uneven appreciation for farmed fish. While US consumers are eating about half farmed fish and half wild fish, the production of domestic farmed seafood is far behind other fish farming countries. Only five to seven percent of American demand for seafood is met by US-based aquaculture - mostly freshwater fish like catfish, trout and tilapia - with marine aquaculture supplying just 1.5 percent - mostly shellfish - of the entire US seafood supply.

Clearly Americans like to eat farmed fish, but we're not big on producing it. As we discussed yesterday, 90 percent of seafood consumed in the US is imported, half of which is from aquaculture. This large gap between demand and production adds up to a seafood trade deficit of over $10.4 billion annually, and so aquaculture could be primed for growth in the US. Yesterday we learned the good and the bad about onshore aquaculture, but today we take a look at marine aquaculture and learn about the techniques used, and how they may or may not always be sustainable.

Near Shore Net Pens

If you've ever looked out on a bay, pond or lake and seen what appears to be a nearly sunken circular or rectangular structure, then you've probably seen a fish pen. These pens are made up of underwater cages or nets where finfish are stocked, artificially fed and harvested when they're ready for market. Near shore pens are notorious for their impacts on the environment and suffer from similar problems associated with industrial feedlots on land. Because of their open design and the high concentration of fish in the pens, fecal waste and excess feed and antibiotics are introduced into surrounding waters. There is also a danger of farmed fish, including non-native and genetically-modified species, escaping from the pens and into the wild where they can outcompete native fish species. Parasites and disease can enter the surrounding ecosystem from fish in open pens.

Perhaps the top concern for all finfish aquaculture, however, is the use of small wild-caught fish as feed for more economically-valuable species like salmon. Important lower food chain species like anchovies, sardines and menhaden have been reduced into feed traditionally for poultry and livestock use, but recently aquaculture doubled its share of global fish meal and fish oil consumption to 68 percent and 88 percent, respectively.

Integrated Multi Trophic Aquaculture

Well that's a mouthful. Basically this is still net pen aquaculture but with the addition of plants and animals lower on the food chain - think seaweed and shellfish - that can gobble up the waste from farmed finfish. Is it more sustainable? It attempts to address the waste issue but it doesn't do anything to prevent disease or escapes. Without any comprehensive studies on its effectiveness, "IMTA" can't claim to be much of an improvement over plain old fish pens.

Offshore Net Pens

Take fish farming several miles offshore and you've got open ocean aquaculture. Unfortunately, the experimental systems used to raise fish far offshore simply move many of the problems associated with near shore pens out of sight, plus they add a higher demand for energy and a larger carbon footprint to manage the remote facilities. Operators of offshore aquaculture are focused on high-value species like salmon, cod and tuna because of higher expenses involved, but these species are typically raised on fishmeal. Offshore aquaculture is presented as a way to offset overfishing pressure from wild stocks and meet consumer demand, but high-on-the-food-chain species depend heavily on large amounts of wild-caught smaller fish as feed to produce small amounts of high-value fish. As currently practiced, open ocean aquaculture consumes more animal protein than it ultimately produces. The US government is all-in on offshore aquaculture, including a push to grow the new industry in the Gulf of Mexico. To this day, however, there are only a handful of open-ocean aquaculture operations in state waters, and none in federal waters. New rules allowing open ocean aquaculture in federal waters are expected soon, however.

Near Shore Shellfish Farming

Oysters, mussels and other shellfish are a refreshing exception to the rule when it comes to aquaculture and sustainability. Instead of introducing waste and pollution to surrounding waters, shellfish, in fact, effectively filter most contaminants out of water and can enhance water quality. Shellfish aquaculture represents about 80 percent of US marine aquaculture production, so the growth of shellfish farms in estuaries around the country represents a win-win for sustainable food production and job growth.


No, seaweed is not fish, but just like shellfish, seaweed represents a unique opportunity for near shore aquaculture that's also beneficial for the health of coastal ecosystems. The global seaweed industry is worth over $7 billion, but only a few companies in the US harvest it. We're not just talking about nori for sushi; numerous kinds of seaweed are used in a number of products, ranging from ice cream to fertilizer to medicine. With their ability to improve water quality, and with only seed and sunlight required to cultivate, seaweed is worth serious consideration by coastal communities looking for green jobs. (If you're really interested, you can even download a kelp farming manual for free!)

Image "Aquaculture" by NOAA's National Ocean Service on Flickr used under a Creative Commons Attribution 2.0 Generic license.