[♪ INTRO] Much of the world’s population depends  on fish as a source of protein, and that demand is only growing.

But lakes, rivers, and oceans  are already overfished, and many fisheries can’t  produce as much as they used to. Which means that fish farming,  also known as aquaculture, is going to need to ramp up to take the  pressures off of wild fish populations.

However, as unsustainable as commercial  fishing has been in the past, aquaculture doesn’t have a  sterling reputation either. Which leads to questions like, is it  possible to farm fish more sustainably? And which one is actually more harmful?

How can we choose what’s best for the environment without giving up on our sushi  rolls and our crab cakes? Well, as you might be expecting,  the answer is not straightforward. So let’s take a look at some  of the positives and negatives of catching and farming fish  to see what comes out on top.

Let’s dive into the environmental  impact of wild-caught fish first: the good, the bad and the ugly. We’re going to consider a handful of  factors: things like greenhouse gas emissions and direct ecosystem impacts, as well as waste and overall efficiency of  different fishing methods. The good news is that  wild-caught fish don’t require any extra space or any water to be brought in.

Because, as the term implies,  they live in the wild. They inhabit naturally occurring bodies of water and eat what is available to  them in their environment. So in comparison to other protein  sources, like pork or beef, they require very little additional  resources before being harvested.

They’re also a relatively easy to  access source of high-quality protein, which is one of the reasons  at least 1 billion people rely on fish and shellfish  as their main protein source. And in general, fish and shellfish are  pretty eco-friendly protein choices. For instance, gram for gram, fish  contains more protein than nuts.

So the greenhouse gas emissions to produce the same amount of protein  are correspondingly lower. The problem is that once the world  caught on that there were literally plenty of fish in the sea, commercial  fishing operations ramped up. Those big ships emit a lot of greenhouse gases.

And there are a lot of them. Worldwide, the total number of fishing  vessels in 2018 was estimated at 4.6 million. Not all fishing operations are created equal, and the emissions depend on  the type of fishing being done.

Shrimp and lobster fishing have  higher carbon emissions because the boats have to travel a  long distance between traps, and constantly stop and start  as they place their pots. Other methods are less fuel-intensive. Purse seine nets are used to capture  large groups of small schooling fish by literally scooping up the  entire school in one net.

They are among the most fuel-efficient  ways to catch a lot of fish at once. Hook-and-line fishing, where a long line  is set out with one or more baited hooks, is also fairly fuel-efficient because the line doesn’t create any additional drag on the boat. However, wild-caught fish  aren’t just eaten locally.

These harvested fish are  shipped all over the world, and shipping comes with its own  set of greenhouse gas emissions. Looking beyond the greenhouse gas  emissions of wild-caught fish, there are a whole host of other  environmental impacts as well. Net trawling, where large fishing  nets are towed behind a ship, can result in a lot of bycatch.

Bycatch is anything caught in fishing nets that is unwanted and inevitably is thrown back as waste. Around 10% of the world’s commercial  fishing intake is discarded as bycatch, which is unfortunately not just  small unwanted fish species. It’s often larger marine creatures like  sharks, sea turtles, dolphins, even seabirds.

Fortunately, practices like hook-and-line  fishing can limit how many creatures are caught accidentally, especially when fishers use a special hook to target the catch they want. Then we have bottom trawling, where weighted nets are dragged across the seafloor. This one is infamous, as it can decimate  entire ecosystems found on the bottom, some of which can take decades to rebound.

Finally, even if we know better now, a lot  of wild-caught fish species in both oceans and lakes have been harvested  unsustainably for a long time. Commercial fisheries took more  than the existing population could replace through reproduction,  so these fish species are going to take a while to rebound, even after  unsustainable practices have stopped. So wild caught fishing methods don’t always get an “A” grade on their sustainability report card.

It’s been proposed that we  should consider supplementing or completely switching over to  farmed fish as a source of protein. But aquaculture has earned itself a  bad reputation as an unsustainable and environmentally degrading practice. So… how accurate is that reputation?

Once again, it’s more complex  than just saying it’s good or bad. Now, from a greenhouse gas perspective  alone, producing more farmed fish would be much easier on the  planet than producing more beef. Cows are notoriously inefficient eaters.

Whereas fish convert the food they’re  given into biomass very efficiently. For some species, it’s like a 1:1 ratio. That means one pound of fish food  can yield up to one pound of fish.

So fish farmers get a lot of bang for their buck. Not only that, but fish and  shellfish often require less space and resources than other protein  sources like chicken or beef. Many shellfish species are grown vertically, and they are pretty small when  compared to other proteins.

And since farmed fish eat what  humans choose to feed them, they can be healthier for us too. Depending on the conditions they’re raised in, farmed fish may have lower levels  of heavy metals like mercury. Farming shellfish plays another important role.

Not only are they a great protein source,  they also help improve local water quality, because many species are efficient filter feeders. When shellfish feed, they pull  water through their bodies, keeping the small particles  and pushing the water back out, so they actually pull a lot  of stuff out of the water. But it’s not all great news for aquaculture.

Fish are often farmed in natural bodies of water, with only a simple pen separating  them from the wild ecosystem. Horror stories abound of farmed fish  escaping their holding pens into natural bodies of water and  competing with wild fish populations. And unfortunately, that can and does happen.

Not to mention, fish are messy. They are messy eaters, and then of course what comes out of the other end is also messy. The extra nutrients coming from  this waste end up building up in the water at the fish farms.

These extra nutrients can lead to algal  blooms and deplete oxygen in the water. Fish farms can also be a  breeding ground for disease. All those fish sharing the same  water and swimming in small spaces makes it easy for them to get sick.

Which means that farmed fish often  have to be given antibiotics. And if they are once again in a  pen in a natural body of water, the antibiotic can easily diffuse out into the ecosystem, affecting surrounding waters. There’s also the possibility that improper  antibiotic applications could lead to antibiotic-resistant bacteria in the water, which has implications for human health as well.

And in some places around the world, the farms themselves are putting  pressure on the surrounding ecosystems. For example, in Indonesia,  an increase in shrimp farming is leading to increased mangrove forest loss. That’s because these coastal  trees are being cleared to make room for more farms.

Finally, some species of farmed fish, like  salmon, are being fed wild-caught fish. These large carnivorous fish require a  lot of smaller, wild fish to sustain them. Not only does this deplete wild-caught resources, it also kind of defeats the purpose  of fish farming in the first place.

But let us return to the topic  of greenhouse gas emissions. Because fish farms might not require  giant boats traveling far and wide, but they still need energy. How much often depends on the species.

For example, catfish farming can be  so resource-intensive that it’s about as bad as beef, at least as far as  greenhouse gas emissions are concerned. But just like with wild caught fish,  the industry has recognized there are some unsustainable practices, and  has implemented many improvements in order to try and address these issues. For example, fish pens are monitored more closely to manage situations where escapes might happen.

And some kinds of fish farms  are being moved inland, where fish can’t escape into the  surrounding wild ecosystem at all. And since they’re isolated from wild populations, that also helps with the spread of disease. Plus, antibiotics that are applied stay  contained within the fish farm itself.

Aquaculturists who want to be more sustainable are also being more conservative  about antibiotic use. They’re using antibiotics on an as-needed basis, instead of administering them to  the entire population upfront. And aquaculturists can also  opt to use fish vaccinations as a way to prevent disease outbreak.

Various improvements can also  be made to aquaculture practices where fish farms are located  in natural bodies of water. Fish farmers can place coastal fish  pens in places with high currents, to help wash away excess nutrients  from fish feed and waste. And better waste management  systems overall can be put in place for those farms that used to drain their  fish waste into the surrounding ecosystem.

Finally, new standards have been created to help ensure more sustainable  fish farming practices. The Aquaculture Stewardship Council has created a set of best practices to improve  fish farming with standardized methods. It’s opt-in, but fish farms can obtain  a certification to signal to consumers that they are following  sustainable aquaculture practices.

In the end, unsurprisingly, there  is no straightforward answer to which is better or more sustainable. Ultimately, what it comes down to is choice. Since you can’t say up front  that something is better because it’s farmed or wild caught,  learning more about where your fish comes from can help you to make  more sustainable decisions.

And there are already programs  in place to help with that! For example, the Monterey Bay  Aquarium Seafood Watch program helps consumers learn about different fisheries, and recommends more sustainable ones. Programs like this one can provide  consumers with information about both wild-caught and farmed  fish, so that we can weigh the pros and cons and make  more informed decisions.

Maybe this is a bit more work than saying  one way is good and one way is bad, but it’s not like an issue this big was  ever going to come down to black and white. Basically, the idea is that we can  make informed decisions without making big categorical judgements  about what kind of seafood is better. Which is great, because man, I could  really go for some crab cakes right now.

Since moving to Montana it’s  just not really been on the menu. Thanks for watching this episode of SciShow, which was brought to you as always with  the generous support of our patrons. If you want to learn more and  maybe get involved yourself, you can check out Patreon.com/SciShow. [♪ OUTRO]