S why fish

Once the microalgae clean the water, it can then be reused in fish tanks or discharged into the sea without causing pollution. The farmed microalgae are ultimately used as food for oysters. However, in order to have a fully functioning sea farm, there must be enough worms and microalgae to clean the water in the tanks and enough microalgae to feed the oysters.

It is often difficult to maintain the perfect balance between the different tanks, because they are easily affected by climate factors like rain and temperature, as well as by the presence of undesirable species, like parasites or organisms that eat algae. This is why researchers are working with fish farmers to find the best ways to connect the tanks and to better control the growth of the species being farmed.

The researchers connected three different tanks: a fish culture tank, a microalgae culture tank, and an oyster culture tank Figure 3. To be sure of their results and to have enough data, researchers always work with three replicates of each experiment, so, in total, there were three fish tanks, three microalgae tanks and three oyster tanks.

This means that if the animals died in one of the tanks, researchers could still get results from the other two. Researchers placed filters between the fish tanks and microalgae tanks, to remove the solid waste produced by the fish. This experiment lasted 2 months, and various measurements were taken. The fish waste was mainly composed of nitrogen N and phosphorus P.

The researchers found that there was almost no waste left in the water when it exited the microalgae tank, because the microalgae had consumed most of it.

The researchers concluded that microalgae are very efficient at removing the N and P waste produced by the fish. To test whether the microalgae are suitable food for oysters, the researchers measured the size of the oysters at the beginning and at the end of the 2-months experiment.

Normally, the more oysters eat, the bigger they are. But surprisingly, in this experiment, the oyster growth was poor, and some oysters did not grow at all. Even the original authors do not stand by this statement. Compared to other meats, seafood has a low environmental footprint when it comes to greenhouse gas emissions, land use, and nutrient pollution — we looked at this in a related article. When we catch fish faster than they can reproduce, these numbers decline. In a previous article we looked at assessments of overfishing: around one-third of global fish stocks are overfished.

As consumers we want to know this to know what types of fish to buy, or where to source it from. At the industry, national or global level we want to know this so we can take action on the stocks that are not doing well. There are several methods we use to better-understand the health of fish stocks. One method is small-scale scientific surveys in specific regions.

The second is to do large-scale stock assessments. These assessments have become the bedrock of fisheries management. The RAM Legacy database — first launched in — is led by a team at the University of Washington — and is the most widely used in research and is adopted by the UN Fisheries Division.

Unfortunately there are key regions where we have very little data. The database is missing data from most Asian, African and Latin American fisheries. We see this in the map, which details the coverage of fish stocks in the RAM database. Most fisheries across Europe and the Americas have good coverage. Most fisheries across Asia do not. But first we should see what we know if anything about the stocks that are missing.

Stock assessments are used by fisheries across the world to understand the health of fish populations, and implement strategies to manage their fisheries. For example, they might be used to set catch limits at levels that are sustainable given the dynamics and health of the fish population. Scientists use acoustics and other methods to monitor and estimate the abundance of fish at any given time. Sampled fish are taken to assess the age and population growth rate of the population.

For example, we might need to know the ratio of adult versus juvenile fish to estimate the reproduction rate of the population. Scientists then used these three inputs — abundance, biology, and catch — to model the population dynamics of the fish stock. Abundance and biology tell us how many fish we would otherwise expect to be there before we remove any.

The balance of these two gives us an estimate of how many there really are. But can we say anything about how they might be doing? This balance can change from season-to-season, or even month-to-month as environmental factors change and affect the dynamics of the ecosystem. Regions that manage fisheries well are constantly monitoring, and changing catch limits when necessary. Fisheries that are not carrying out these assessments will struggle to maintain this balance.

Fishing pressure in many of these regions is intense. Bottom-trawling — where large fishing nets are dragged along the seabed — is very high in countries such as China, India and Indonesia. Maintaining such high rates of fishing without monitoring them closely makes it unlikely that fish stocks are in a healthy state. One of the ways that we can assess the pressure from trawling is to look at how many times a given area of the seabed is trawled.

Some areas are only trawled once every few years. Others are trawled over and over. Research suggests that where stocks are healthy, a net only passes over the same spot once in a period of 3 to 10 years. This has been confirmed from some smaller scientific surveys in the region.

Scientific surveys have periodically monitored stocks in the Gulf of Thailand for decades. They show a large reduction in fish stocks over time. Other surveys of trawling efforts across the region show similar declines. Ask local experts about the state of fish stocks and most have a similar take: they are in poor condition. Some will be well-managed and healthy. It so happens that these tend to be richer countries: those across Europe, North America, Australia and Japan.

This database covers over 1, of these fish stocks. In the chart we see how these stocks are doing. It shows the biomass of fish populations.

That is, essentially, the amount of wild fish there. The Maximum Sustainable Yield is the sweet-spot where we can catch as much fish as possible without reducing that fish population below the most productive level. Fish stocks are healthy across most of these regions. However, there are a few regions that are not doing so well. The Canadian East Coast has seen a large decline in recent years. Assessed stocks in South America and Africa are struggling.

The European Mediterranean is not doing well. This is reflected in the fact that the Black Sea is very overfished. Whether a fish stock is doing well or not is mainly determined by its fishing intensity: what fraction of the population is being caught each year. In this chart we see levels of fishing intensity across the same regions. An optimal value is one. Fish stocks tend to be a lagging indicator to fishing intensity.

So, if we hold fishing intensity too high above one — even if only slightly — then stocks will inevitably fall below one until fishing pressures are reduced. In the chart we see the same metric as before — fish stocks measured by biomass — across different types. Many of our most popular stocks are well-managed and have healthy populations. A few groups are not faring so well. In recent years mackerels have dropped below the optimal level due to increased fishing intensity. And sharks are declining rapidly — a worrying trend.

The health of tuna populations has been a concern for decades. We often hear that tuna are being overfished to extinction. That we should avoid them if we want to eat sustainably. But many tuna populations are now well-managed. Previously we looked at the aggregate of tuna stocks; we can zoom in further and look at particular regional stocks.

In the chart we see the health of fish stocks across three oceans: the Atlantic, Pacific and Indian Ocean. The trend looks worse for those in the Indian Ocean. Its stocks have now fallen below one, and look to be continuing downwards. Atlantic and Pacific tuna might be a reasonable fish choice. Tuna from the Indian Ocean has less guarantee of being from a sustainable source. But we can go even further and look at specific tuna species, such as bluefin or yellowfin.

We see these stocks in the chart. Many tuna species have seen a significant recovery through improved management — especially in US and European waters. From the chart we see that most are above one: the maximum sustainable yield. Many of the tuna stocks that were the biggest concern have managed to turn things around.

We see this in this chart, which now shows fish stocks measured as their total mass in tonnes , rather than relative to the maximum sustainable yield. Throughout the s, 70s, 80s, and 90s we see a massive decline in tuna populations. The Western Pacific yellowfin fell by three-quarters. But, since the millennium, better management of fisheries and reduced overfishing means that many of these stocks are recovering. However, there are a few species that are still of concern. This is a positive sign.

They are recovering but still need more time to return to sustainable levels. We saw previously that shark stocks were now below the maximum sustainable yield, and continue to decline. We see this again in the chart here. Many more stocks have not been assessed — and these are likely to be in regions where monitoring is poor; and illegal catch is poorly regulated. There, shark populations might be in even poorer health. For general readers, this might be too detailed.

But it could be useful for those with a background in this area to explore specific fish stocks. One of the best ways to reduce our impact on the environment is changing what we eat. The research shows us that we can have the biggest impact by eating less meat and dairy. Or, substituting lower-impact meats such as chicken and pork for beef and lamb. Is that an environmentally-friendly option? There are lots of types of seafood: not only different species, but also ways of producing them.

We can catch them in the wild, or grow them in fish farms. In a new study published in Nature , Jessica Gephart and colleagues conducted a meta-analysis of the impacts of fish and seafood across multiple environmental metrics.

It covered over fish farms, and records from fisheries. These results look at the impacts on-farm and off-farm, up to the farmgate. That means, up to the point that harvested or caught fish are brought back to land. It includes all of the inputs into production, such as fish feed, or fuel use on fisheries. It does not include post-farm processes such as transport to retail, packaging or cooking.

The impacts across the seafood products are shown in the charts. Comparing fish to other types of fish is useful. But we also want to know how seafood compares to other protein foods. Overall we see that seafood has a relatively low environmental impact among animal protein sources.

Most farmed seafood needs less land and freshwater, and causes less nitrogen and phosphorus pollution. This is because fish tend to be more efficient than chickens in converting feed into meat: that means they need less feed per kilogram. There are some exceptions though: wild flounders, lobsters, and shrimp, for example, can have a high carbon footprint. More than double that of chicken. Looking at the median footprints allow us to make quick, general assessments of the high- and lowest-impact species.

This makes little difference for some species, but for others it can have a large impact. In the chart we see the spread of greenhouse gas emissions among the different types of seafood.

The median of each — as we looked at above — is shown as the thick black line for each bar. The width of the bar shows us how variable this can be: it tells us what the largest and smallest impact can be for each species. Wild-caught seafood is shown in blue; farmed seafood in red. Now we see that not only are there large differences in the median between each. There are also large differences in how variable emissions can be. In general we tend to see that the impacts of farmed seafood are much less variable than wild-caught; the red bars are much thinner than the blue.

The median emissions for farmed and wild-caught salmon are similar; farmed has a slightly lower footprint of 5. But the big difference comes from the spread of emissions: wild-caught can range anywhere from 1. Farmed salmon only ranges from 4. If you choose wild-caught salmon you could be picking a low-carbon, or a high-carbon protein source. It might even be lower than farmed salmon. But if you pick farmed salmon you are almost guaranteed that it will be relatively low-carbon.

We see this across other species too: see shrimp, for example. The same is true in our comparison to chicken. Chicken has a very low variation in footprint. Some choices that will guarantee a relatively low footprint are farmed bivalves mussels, oysters and scallops and seaweed — these are filter-feeding organisms which also sequester carbon and nutrients in their shells. That is partly why they have such low emissions; and they need no additional land either.

Farmed salmon, trout, carp and catfish are also good choices. Again, we should be clear that the most effective way to reduce the impact of your diet is to eat less animal-sourced products overall. On the basis of total protein and calories, plant-based foods such as legumes and soy still have a much lower impact. But for those who do not want to eliminate animal products completely, seafood can be a good choice.

Many types of seafood have a lower impact than chicken. This means they have a much lower impact than foods such as beef or lamb. The sustainability of wild fish stocks is not something that we discuss here, but is a crucial metric to consider. We will cover that in much more detail in a follow-up article.

But the headline summary is that the status of wild fish stocks is mixed. Effective management of fisheries across Europe, and North America means that many of these fish stocks are stable and no longer in decline. That matters for where you source wild-caught fish from: sourcing from European or American fisheries might be a safer choice if you want to ensure they are sustainable. The issue of wild fish stock depletion is not an issue for farmed seafood.

An industrial park in Appalachia may seem an odd place to grow a few million natives of the Nile. But industrial-scale fish farms are popping up everywhere these days. Aquaculture has expanded about fold since In its global output, from silvery salmon to homely sea cucumbers only a Chinese cook could love, reached more than 70 million tons—exceeding beef production clearly for the first time and amounting to nearly half of all fish and shellfish consumed on Earth.

With the global catch of wild fish stagnant, experts say virtually all of that new seafood will have to be farmed. So they want it to be right from the start.

Tilapia pens in Laguna de Bay, the largest lake in the Philippines, are choked by an algal bloom they helped create.

The overstocked lake produces large numbers of farmed fish, but excess nutrients trigger blooms that use up oxygen—and kill fish. Aquacultural pollution—a putrid cocktail of nitrogen, phosphorus, and dead fish—is now a widespread hazard in Asia, where 90 percent of farmed fish are located. To keep fish alive in densely stocked pens, some Asian farmers resort to antibiotics and pesticides that are banned for use in the United States, Europe, and Japan. The U. In and the FDA discovered numerous banned substances, including known or suspected carcinogens, in aquaculture shipments from Asia.

Nor have fish farms in other parts of the globe been free of problems. The modern salmon industry, which over the past three decades has plunked densely packed net pens full of Atlantic salmon into pristine fjords from Norway to Patagonia, has been plagued by parasites, pollution, and disease. A disease outbreak in virtually wiped out the shrimp industry in Mozambique. Chinese farmers started raising carp in their rice fields at least 2, years ago.

Farmers stock their ponds with fast-growing breeds of carp and tilapia and use concentrated fish feed to maximize their growth. That is my duty. To make better fish, more fish, so farmers can get rich and people can have more food. The farm produces 30 million pounds of fish each year from its ponds.

The fish are vegetarians: their feed is made from soy, corn, rice, wheat, and cottonseed meal, with no antibiotics. Mouth brooding—along with rapid growth, a vegetarian diet, and the ability to thrive in dense populations—helps make the tilapia an easy fish to farm.

A tilapia reveals a mouthful of eggs that will be extracted for hatching at a farm. How to do that without spreading disease and pollution? For tilapia farmer Bill Martin, the solution is simple: raise fish in tanks on land, not in pens in a lake or the sea.

You compare that with a percent controlled environment, possibly as close to zero impact on the oceans as we can get. To keep his fish alive, he needs a water-treatment system big enough for a small town; the electricity to power it comes from coal.

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