Is Aquaculture a Sustainable Move Forwards?

Aquaculture is set to be an ever-increasing part of our future as we seek new ways of sustaining our growing global population. It provides an opportunity to feed our planet without taking up more valuable land space, whilst it also hopes to reduce the pressure on wild fish stocks, many of which are on the verge of collapse after decades of overfishing. With the ocean covering 70% of Earth’s surface area but only providing 5% of our current food supply, there seems to be an enormous amount of untapped potential. However, the question remains, can we actually make aquaculture as sustainable as it is hyped up to be?

Aquaculture is simply the controlled farming of fish, shellfish and aquatic plants, such as seaweed, with the aim of increasing food availability whilst minimising environmental damage and protecting our natural species. There are some great success stories where not only have fish or plants been cultivated effectively but they have also provided the environment with a range of benefits too. For example, oysters filter feed and eat the natural plankton floating in the ocean currents, meaning we don’t have to provide food for these popular farmed creatures to eat. Whilst they filter microscopic pieces of food out of the seawater, they also filter nutrients, biotoxins and bacteria, which means they help clean our seas by removing fertiliser chemicals, pollutants and pathogens in areas where they are farmed. Seaweed cultivation is also on the rise; as well as producing a healthy, vitamin packed food source, seaweeds also absorb enormous amounts of carbon dioxide as they grow, helping draw carbon out of our atmosphere and reduce the effects of climate change.

Unfortunately however, not all farmed species have such a great story to tell. One of the main sustainable qualities of aquaculture is that it is the form of meat production which provides the greatest return on the feed put in. Yet when we look a little closer, it is this input which can be incredibly damaging to the environment. Farmed fish mostly eat fishmeal which is a condensed powder made from ground dried fish. In order to produce fishmeal, wild anchovy, mackerel and sardines are caught and processed before being fed to farmed species. You might ask, why not just eat the original fish? This is why, in order to make aquaculture sustainable, we need to get as close to a 1:1 ratio of food input to produced meat as possible, otherwise we are catching and killing more fish than we are breeding and eating. Some species are naturally very efficient when it comes to eating, such as barramundi, yet other popular favourites such as tuna need to eat an astonishing 12kg of food to produce only 1kg of fish. Scientists have already discovered how we can create omega 3 fatty acids from yeast in order to supplement the diet of farmed fish without the need for smaller fish but currently this is not enough and the fishmeal industry continues to boom.

It is in this industry which feeds aquaculture that many issues lie. Chimbote, a coastal city in Peru, is the heart of the fishmeal industry and you can smell its streets before you catch sight of its buildings. The Humboldt Current, which lies off the coast of Peru, provides the country with easy access to one of the most productive marine ecosystems in the world and alongside that comes a huge abundance of anchovy, a key staple in fishmeal. As the biggest exporter of this product globally, Peru shipped over $1.5 billion worth of fishmeal in 2019, much of it becoming animal feed. Whilst this might be great news for the aquaculture industry and the national economy, it has left the local fish and seabird populations in decline as such enormous removal of anchovy has thrown the delicate ecosystem off balance. In addition to this, pollution from the processing factories in the city pours into the sea and has culminated in a one metre thick sludge on the seabed. This foul-smelling sludge holds little oxygen and is sending the coastal area on its way to becoming a dead zone, void of marine life. The fishmeal industry is very difficult to regulate as fish are caught all around the world by giant floating factory vessels in multiple countries which all have varying levels of environmental protection. This low level of traceability makes it difficult to determine whether the input into aquaculture is marine-friendly, making us question whether aquaculture can be genuinely sustainable.

Of course, many people are working to shift aquaculture’s reliance on fishmeal derived from wild fish. In Australia, some are using offcuts of fish caught for human consumption to create fishmeal, ensuring no part of the catch is wasted. Others are looking to more extreme alternatives, with soy being added to fishmeal to increase protein levels whilst insects and algae are also thought to be able to provide essential nutrients to farmed fish.

Yet the source of food is not the only sustainability question mark hovering over aquaculture; the fish stock itself also poses a problem. Many farmers have a broodstock, which is a group of mature fish they use to lay eggs to produce the fish which will be sold to markets. However, others use the ranching method, which sees wild fish caught and raised to a larger size within the farm before being replaced by more wild fish. This method still sees our declining wild fish stocks targeted and worst still, many of these are taken before they reach reproductive age, meaning our natural stocks are going to continue struggling to recover. Examples of this ranching include young eels which are caught and farmed for unagi used in sushi whilst juvenile bluefin tuna are another lucrative catch for farmers.

One of the most potentially dangerous issues with aquaculture however, is arguably disease. If we take certain species and place them in environments they are not suited to, such as barramundi in cool waters or salmon in warm waters, they become stressed and more vulnerable to disease. Infections are also more likely to spread in farms due to a high density of fish in such a small area whilst the mixing of old and young fish can exacerbate the problem too. In Tasmania, over one million farmed salmon died recently which is thought could have been due to the mixing of age groups. The greatest threat is that these parasites and diseases then enter wild populations of fish, giving them yet another problem to contend with alongside climate change and overfishing.

Keeping aquaculture and our wild ecosystems separate is actually a large problem and it is not just disease which can cross the barrier but the fish themselves, most often due to holes in the nets. It may not just be the odd one or two escape artists who break free either but thousands of fish have been known to take off into the wild after storms or predator attacks have damaged the pens. The danger here is that sometimes fish are not farmed in areas where they are native and once escaped, they can infiltrate local ecosystems and disrupt the delicate balance by outcompeting native species for food or even forming a direct predator to them. This places great pressure on wild species and in particular our most rare and vulnerable. Even if fish are farmed in an area where they are native, there is the risk that they will breed with wild individuals and over time this could impact their genetic makeup and the offspring may be less suited to surviving in the wild.

Finally, and of course, pollution is another harmful body which could pass from the farming sites into the ocean as wastewater full of nitrates often either freely flows from the farms into the ocean or is directly dumped from ponds into nearby watercourses. Pollutants in this water can be natural, including fish faeces and uneaten food pellets but also chemicals. Pesticides and antibiotics are frequently used by farmers to reduce the number of parasites and therefore disease but can wreak havoc in the ocean. The high level of nutrients in pesticides can cause a bloom of algae and in a worst case scenario, eventually a dead zone in the surrounding area whilst antibiotics in the ocean could lead to an increase in antibiotic-resistant bacteria.

As you can see, there are a lot of factors we need to control and monitor more tightly if we want aquaculture to be the sustainable future of food that many people want it to be. With this form of farming only set to grow alongside an expanding and hungry population, it is essential we get it right this time and find the most efficient and environmentally-friendly way forward. What are your thoughts on aquaculture?

By Neve McCracken-Heywood