In this article, we will be looking at the environmental impacts of aquaculture, and how they compare to the impacts of conventional fishing. In case you haven’t read the previous article, I answered some common questions people have when it comes to aquaculture as a source of our fish. Aquaculture for those unfamiliar with the term is essentially the commercial farming of fish and other marine organisms for consumption.
Is aquaculture actually sustainable and/or environmentally friendly? How does it compare with conventional fishing practices? Well, let’s dive into it!
Environmental Impacts and Sustainability of Aquaculture
Simply put, aquaculture has negative environmental impacts if not properly carried out. But these problems can be and have been minimised with proper practices, and in some cases even result in positive environmental impacts.
Aquaculture ponds in the Northern Territory of Australia (CSPIRO/The Fish Site, 2020).
Brackish water fish farming in Malaysia (Hatchery International, 2019).
One core problem is the organic waste and uneaten feed which contain nitrates and phosphorus. In high density aquaculture farms, these are concentrated in one place when the farms are not located in moving currents or if the waste is not treated (Wu, 1995). This impacts water quality in that area, and could result in eutrophication (Chislock and Doster, 2013). Poor water quality has knock-on effects on the health of the fish, as it can irritate their gills or cause other health problems and diseases (Mannan et al., 2012). Eutrophication is the increased growth of algae from extra nutrients in the organic waste. This can be extremely detrimental for the ecosystem as it results in oxygen deprivation and the formation of dead-zones of low or no oxygen (Chislock and Doster, 2013); and the ecosystem may collapse. In this day and age, aquaculture farms are mostly set up in the right areas to prevent things like this from happening and work to treat waste adequately, but there are still cases where this could happen.
One of aquaculture’s positive environmental features is its high resource efficiency in producing protein. It has a much lower feed conversion ratio, which means the amount of feed required to produce the same amount of protein is much lower for fish and shrimp compared to other proteins (Tacon and Metian, 2008); it takes less feed to produce a kilogram of fish than other meat. This is very sustainable as less feed crops need to be grown, potentially reducing cropland pressure. A whopping 36% of the world's cropland is used for animal feed (Cassidy et al., 2013). Food security could get a boost combining fish protein with land available for food crops.
Besides that, another positive environmental impact is that the farming of seaweed and bivalves are beneficial to water quality (Buck et al., 2017). Bivalves are filter-feeding shellfish and are a type of extractive aquaculture, given this name due to their feeding habits extracting nutrients from the water (Buck et al., 2017). This prevents the aforementioned nutrient build-up from the farming of other fish species. They are sometimes farmed alongside other fish species to help combat the issue in a farming method called integrated multi-trophic aquaculture systems (Correia et al., 2020)! Think of this as an improved farm ecosystem. Species within the same trophic level share the same function in the food chain. Essentially you have both fish and shellfish on your aquaculture farm, where fish are in a higher trophic level while shellfish are on a lower trophic level, each playing a different key role in the system.
In terms of sustainability, aquaculture could improve the sustainability of wild fish stocks obviously. If we are farming more fish, we eat and demand less wild fish, therefore there should be less pressure on wild fish stocks . (If you have any questions about farmed fish vs wild fish, check out the previous article in this two-part series, where I look into common questions you may have about aquaculture.) The table below displays the most commonly caught endangered wild-fish species, which a conscious consumer might avoid. For example, tuna is the most popular wild-caught fish in the world, with about 4.6 million metric tonnes caught in 2018 (FAO, 2018). Furthermore, WWF points out that with population pressure, and 3 billion people already relying on seafood as a main source of food, aquaculture can help keep up with increasing demand without further pressure on the wild fish stocks (WWF, 2020a).
Environmental Impacts and Sustainability of Conventional Fishing
Before we get into any of these impacts, we will need to spend a little time on the types of fishing the world carries out. Let me ask you a question. Visualise the first thing that comes to mind when I say the word ‘fishing’.
You probably pictured an angler sitting by a lake leisurely, waiting for the fish to bite. Was I right? What I’ve described is recreational fishing. Unless you are going out to catch endangered species of fish, or on a week-long trip with a strict catch and don’t release policy, the average recreational angler won’t have much impact on fish stocks. The next type of fishing would be small-scale commercial fishing. This would be the ‘nelayan’ (fisherman) you see go out to fish in the coastal communities of Malaysia to make a living for themselves. This doesn’t really have a large impact on the environment or sustainability, as the amount of fish caught is usually in small amounts relative to the heavyweight I'm about to introduce. You probably guessed it, large-scale commercial fishing. This is industrial fishing with large trawlers or boats that are capable of catching and storing large amounts of fish.
Large scale commercial fishing is the problem here.
This involves a plethora of destructive and unsustainable fishing methods when not regulated (Pauly, 2006). It is NOT sustainable at all if left to its own devices. There is a world where such conventional fishing can be sustainable, but this is a highly unlikely scenario. Unless we regulate it, we face the Tragedy of the Commons. Essentially, firms will continue to exploit the fish stock resource as negative externalities (third-party costs caused by these firms), are not borne by them since no one ‘owns’ the oceans. Thus they continue to reap profit from fishing until there is no more profit to be gained, and overfishing is the norm as the full cost of doing so is not borne by them (Hardin, 1968).
So what do we mean by sustainable? Sustainable fishing would require a certain sustainable level of fish to be caught annually. This level is called the maximum sustainable yield, which is equal to the level of growth of the fish stocks (Maunder, 2008).
What are the environmental impacts of volume-driven, unsustainable conventional fishing? First, methods such as bottom trawling and drift or gill nets are extremely dangerous to marine ecosystems and their denizens. Let’s take drift nets as an example. These are huge nets that are placed in the water column to catch anything and everything. Marine mammals, larger creatures and other fish species not being targeted end up in these nets as well, and die as bycatch (Lewison et al., 2004). Furthermore, these types of nets usually catch whole schools of fish, not leaving any behind to reproduce (FAO, 2020a). The damage does not stop there. Pieces of fishing gear might be discarded, or are abandoned if damaged or stuck on structures. These are near permanent environmental hazards for marine life, with more than 100,000 dolphins, whales, turtles and seals caught in abandoned gear annually (UNEP, 2018).
Second, commercial fishing can destroy marine habitats and the seabed. This is an issue commonly associated with bottom-trawling, where large nets are dragged along the seabed to catch bottom-dwelling fish (FAO, 2020b). This completely destroys coral, sponges and other structures used as shelter for marine life. Coral reefs are key nurseries for many species, and damage to them adds to further fish stock decline on top of overfishing (Ecol et al., 2006). Another type of fishing involves dredging for clams in the sea-floor itself. This basically digs up the seabed, churning up sediment that is detrimental to water quality (Todd et al., 2014). This also dislodges worms and microorganisms whose actions are crucial for keeping the seabed habitable and supplied with oxygen (Coleman and Williams, 2002).
To conclude, aquaculture is the future, unless we find a way to reliably regulate the commercial wild-caught fishing industry. Proper regulation is extremely difficult due to the nature of the resource, and it is also hard to enforce on the high seas. A prime example is the super trawlers fishing off the coast of the UK now, as they scramble to exploit the UK's fishing grounds before Brexit happens, even when they are supposed to be regulated under EU regulation (Dalton, 2020). Even when people do care about preventing overfishing, there are also huge issues. In the EU for example, while they supposedly lead the push towards sustainability standards in food chains, only 1% of their marine protected areas out of about 3000 are protected by fishing bans (McVeigh, 2020). This shows us that aquaculture is the more sustainable and environmentally friendly option, and has obvious property rights and responsibilities, along with potentially easier regulation.
I hope this and the previous article has given you some insight into the world of aquaculture. Till next time!
By Robin GOON, Segi Enam intern, 25 Jan 2021 | LinkedIn
Edited by KHOR Yu Leng and Nadirah SHARIF