Humans eat more farmed seafood than wild, and farmed fish production surpassed wild capture fisheries for the first time in 2014. As farmed seafood becomes more and more prevalent in our diets, it is important that the seafood be raised sustainably so that the environment is impacted as little as possible. Just like there are sustainable and unsustainable methods of catching wild fish, there are also sustainable and unsustainable methods of farming fish.
Hand harvesting refers to the manual extraction of seafood species. Hand harvesting is a selective method of fishing/farming as humans visually identify the seafood species before harvest. This avoids the extraction of non-targeted species, and minimizes habitat damage.
Off-bottom farming is typically used to farm shellfish such as mussels, oysters, clams, and scallops. Floating rafts, bags, or suspended ropes are used to grow the shellfish. This system makes no contact with the seafloor, and the shellfish are harvested with little to no bycatch. Since shellfish are filter feeders, they offer ecosystem benefits by reducing nutrient load in the water. They also do not require any external feed as they extract nutrition from plankton in the seawater. This means that shellfish farming puts no pressure on wild fish stocks for feed.
On-bottom culture is a method of farming shellfish on the beach. Shellfish are typically transferred from hatcheries and seeded onto the beach where they continue their grow-out. On-bottom culture is usually a sustainable way of farming.
Open Net Pens
Open net pens can be problematic because the farmed species are in direct contact with the ocean ecosystem. Waste water can affect the benthic habitat directly below the farms, and there is the risk that if farmed fish develop diseases and parasites, these can be passed on to wild populations. If any farmed fish escape from the pen, they can negatively affect wild populations by competing with them for food and habitat. Hybridization with wild individuals is also a concern, since this could produce genetically less fit offspring and compromise the quality of the wild population. If antibiotics are used in the net pens, their open nature and direct contact with the environment makes the potential for spread of antibiotic resistance in humans a serious concern.
Shrimp farmed in ponds in Asia can be unsustainable when sensitive mangrove forests are destroyed in order to make space for shrimp ponds. These mangrove forests are critical to the functioning of the ecosystem as they serve as important fish nurseries where juvenile fish can take cover from predators. Deforestation of mangrove forests affects fish populations in the ocean. Management can also be unenforced, leading to the use of illegal or uncontrolled use of chemicals such as certain antibiotics, fungicides and pesticides in the ponds. Ponds can be sustainable if they are located in areas that are not ecologically sensitive, if the water is treated before discharge or recirculated, and if there are adequate management measures and enforcement in place.
Raceways consist of water running through a channel where the fish are contained. The water is often diverted from a natural water body. If untreated, wastewater can contaminate waterways and spread disease, but this risk can be eliminated if the water is treated before being discharged. Unless there are prevention measures in place, there can also be a risk of farmed fish escaping and impacting wild populations.
Recirculating Aquaculture Systems (RAS)
Land-based tanks avoid many of the environmental risks associated with open net pens. The use of filtration systems to remove solid and particulate waste allows for the water to be reused and recirculated throughout the farm. Escapes are almost impossible as fish are on land in tanks and any disease or parasite outbreak is contained and won’t risk impacting wild populations.
Silvofisheries are a sustainable alternative to traditional shrimp ponds. Shrimp are raised within the mangrove forest, and farmers are often required to maintain a certain minimum cover of mangroves. No external feed is given to the shrimp, as they feed off the natural forest resources. Chemicals are not used, and disease is controlled by not overcrowding the shrimp.