By Shi En Kim for Sentient.
Broadcast version by Suzanne Potter for California News Service reporting for the Sentient-Public News Service Collaboration
Deep below the surface of the ocean are the parts left mostly unexplored and where sunlight barely touches. One of these is called the mesopelagic layer, so-named for its spot in the middle of the pelagic zone. This "twilight zone" of the ocean contains more fish than at any other depth: estimates range from 1 to 10 billion metric tons. Until recently, the fish that dwell there remained mostly untouched by fishing vessels. But growing demand for farmed fish spurred the industry to explore new depths, urgently looking for more tiny fish to use as feed.
The "twilight zone" contains 90 percent of the ocean's total biomass in fish. These strange-looking creatures are well-adapted to the constant pall at 660 to 3,300 feet below. They often sport googly eyes, translucent bodies and bioluminescent veneers. Appearance and color aren't important considerations for citizens of a world shrouded in near-darkness.
What the dwellers lack in looks, they make up for in numbers. Since that remains a driving argument for fishing there, researchers have called for a moratorium to prevent future exploitation.
There Are Plenty of Mesopelagic Fish (For Now)
You can't order mesopelagic seafood in a restaurant or find it at the seafood counter. But there is plenty of seafood industry interest in mesopelagic fish - for turning them into fish oil supplements or aquafeed.
Aquaculture has long been touted as a way to relieve the burden on wild fish operations. Yet the industry itself needs wild fish to operate. Most aquaculture operations use small wild-caught fish, such as anchovies, as fishmeal for larger predatory fish that humans normally put on their plates. While the UN's Food and Agriculture Organization researchers say data on exact numbers is scarce, research suggests at least some fishmeal stocks are teetering towards depletion. In West Africa, for example, feedfish have been over-harvested by foreign companies. And illegal operators are devastating marine biodiversity, and threatening local livelihoods.
As a substitute for wild-caught feed, some aquaculture operators raise their fish on a vegetarian diet such as soy. But many experts are quick to point out the inanity of this alternative: it's like forcing a lion into an herbivore lifestyle, Xabier Irigoien, a researcher at AZTI and King Abdullah University of Science and Technology tells Sentient. "We are actually using land and freshwater to grow soy - to grow a fish that really doesn't need freshwater or land. So we are doing really odd things in terms of food."
At the same time, our global appetite for fish, especially farmed fish, continues to rise, and the industry is exploring new options. In late 2023, the Norwegian firm Nofima conducted a three-month trial of feeding farmed salmon mesopelagic catch. The researchers observed their salmon growing faster than their counterparts fed a typical protein diet. "It's very promising," Ingunn Marie Holmen, a research manager in fisheries technology at the Norwegian research institute SINTEF Ocean, tells Sentient. Nofima "had to actually stop the trial one week early because they ran out of feed."
Not everyone is on board, however. Since 2020, researchers have called for a global moratorium on mesopelagic fishing, concerned that plumbing these new depths for fish could take a toll on climate action and biodiversity.
Fish Capture and Store Carbon in the Sea
All fish, including mesopelagic fish, play a vital role in sequestering atmospheric carbon, slowing the pace of climate change by taking emissions out of the atmosphere. Deep-dwelling mesopelagic fish are even more vital to that process, simply because of where they live. Many of these fish undertake a daily vertical migration, surfacing at night to feed, then returning during the day to hide from predators. Mesopelagic fish exhale carbon dioxide, poop and themselves get eaten by other mesopelagic hunters. And all of these activities help ferry carbon from surface waters to the deeper ocean, where it can be stored more effectively than on land.
Another ecological downside of mesopelagic fishing is the damage to ocean biodiversity. The role of mesopelagic fish in the marine food web is still largely unknown. But researchers know that several epipelagic species, such as dolphins, swordfish and tuna, feed on their submarine neighbors. Trawling in the mesopelagic zone might risk disrupting fisheries at the ocean surface, including those the industry thinks of as the most valuable at market.
"We don't know the system well enough to start harvesting mesopelagic fish," says Middle East Technical University oceanographer, Deniz Dişa. Last June, Dişa and her team published a study modeling the impact of mesopelagic fishing in the mid-Atlantic Ocean. The researchers found that even removing a conservative fraction of the mesopelagic stock would lead to cascading effects of carbon cycle disruption, with a decrease of 14 percent in total carbon movement, and food web chaos. According to the team, fishing in mesopelagic waters would only have a 20 percent chance of being sustainable.
The bottom line, Dişa says: the consequences are "not that simple." And a growing number of ocean researchers agree, arguing that fishing deeper isn't a solution to dwindling marine stocks - it only punts the problem from one corner of the world to another. Given their unique ecological roles in biodiversity and carbon sequestration, mesopelagic fish are just as worthy of protection as those near the surface, if not more.
"This is a group which is unlike most of the species that we exploit at the moment," says Callum Roberts, a University of Exeter marine biologist who is among those calling for a mesopelagic fishing ban. "If there's any part of the ocean that you really don't want to mess with, it's the mesopelagic fish."
Technological Hurdles Add Another Layer of Caution
For now, there are a number of challenges keeping mesopelagic fishing at bay. Experts say this type of fishing requires high fuel consumption, for one. The fish are also very small, some no larger than a finger pad, so fishers need to deploy nets with fine mesh and contend with high levels of drag.
Mesopelagic fish also spoil easily because they're full of digestive enzymes, so they have to be processed or frozen promptly. "You almost can't touch it before it's all porridge," Holmen says. According to marine scientist Stein Kaartvedt, one South African ship's mesopelagic bycatch apparently caught fire because it was so oily.
The fish that hang out in the twilight zone can also be tough to catch. Most are stragglers - they don't congregate while swimming to make for an easy one-scoop kind of bounty - and they are also notorious for dodging nets.
"They are everywhere," says Kaarvedt of the University of Oslo, but that doesn't mean they are easy to catch. "The main thing with fishing is not whether we have 1 billion or 10 billion, but whether you have sufficient concentrations to make fishing feasible."
Mesopelagic Fish Ended Up a Red Herring
The Norwegian fishing industry seems to have come to the same conclusion. In the late 2010s, a group of companies conducted a trial of mesopelagic fishing. The vessels brought in abundant catch in their first attempt, but the next two tries yielded near-empty nets. Since then, the fishing industry there has moved on to more lucrative targets, such as cod and herring. Mesopelagic fishing interest has also watered out in Iceland and South Africa, in favor of mackerel and sardines.
Across the world, more of the fish we eat comes from farms rather than wild-caught fisheries these days. But the proportion of fish stocks that have been classified as overfished has also been growing in tandem. Today, that fraction is 30 percent; and fish populations that are at capacity come in at 60 percent.
Although practically unnecessary at the moment, a moratorium on mesopelagic fisheries would help thwart future exploitation, says University of Exeter's Roberts. Nevertheless, all that research on the mesopelagic zone is far from wasted, industry proponents say. This is a rare instance of a marine industry sinking time and money into conducting a full cost-benefit analysis before diving in head first. "It could be an example of how to approach expansion of any kind," says another researcher, Irigoien, for fish as well as other ecosystems and natural resources.
Shi En Kim wrote this article for Sentient.
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June is World Oceans Month and California environmental groups are highlighting advances in zero-emission shipping.
International shipping emits more than 1 billion tons of carbon dioxide every year, and 40% of U.S. container shipping passes through the Ports of Long Beach and Los Angeles.
Grace Healy, deputy director of the climate program at the nonprofit Pacific Environment, said it contributes to climate change and the resulting air pollution can shorten life spans by up to eight years in neighborhoods near the ports.
"Children in communities near these ports like Wilmington, San Pedro, West Long Beach, they face dramatically higher rates of asthma, bronchitis and cancer risk that's linked to diesel emissions," Healy explained.
California is a leader in clean shipping and passed a rule in recent years to require ships to plug in while onshore and shut off idling engines. Another mandate led to the first electric tugboat in San Francisco and a zero-emission ferry in San Diego. Shipping giant Maersk now runs a container ship on methanol.
Healy added in the next few years, the Golden State plans to tackle regulations on pollution from container ships.
"The California Air Resources Board has also stated they are going to work on an in-transit rule for oceangoing vessels," Healy noted. "That's really exciting, because those container ships are really, really dirty."
The future is uncertain for the federal Clean Ports Program, which supports the transition to zero-emission shipping. Money awarded last fall before President Donald Trump took office should be safe but the U.S. House of Representatives recently voted to gut the program as part of the Republican funding package known as the "One Big Beautiful Bill Act." The Senate version, which has yet to get a vote, appears to leave the language out.
Disclosure: Pacific Environment contributes to our fund for reporting on Climate Change/Air Quality, Energy Policy, and Oceans. If you would like to help support news in the public interest,
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By Seth Millstein for Sentient.
Broadcast version by Suzanne Potter for California News Service reporting for the Sentient-Public News Service Collaboration
The global population is projected to hit at least 8.5 billion people by the end of the decade. As more of us become aware of the disastrous environmental impacts of livestock production, some climate-conscious consumers are turning to seafood as an alternative to meat. But the seafood industry has its own problems, as the rise of overfishing - and its harms - has made clear.
"Overfishing is a serious global problem, threatening ocean wildlife and biodiversity, as well as seafood supplies," Dr. Beth Polidoro, Director of Research at the Marine Stewardship Council, told Sentient in a statement. "And unfortunately, it's a problem that's increasing, and has been for several decades."
Seafood consumption has risen dramatically since the mid-20th century: Between 1961 and 2021, the average person went from eating around 20 pounds of seafood every year to around 44 pounds, according to Our World in Data. Since then, commercial fishing has become a $229 billion industry, and according to a 2019 study, between 1.1 and 2.2 trillion fish are caught every year.
But as our appetite for seafood has increased, so has the frequency of overfishing. Between 1974 and 2017, the share of the world's oceans that were overfished jumped from 10 percent to a little over 34 percent, according to the Food and Agriculture Organization of the United Nations. Marine ecosystems around the world have suffered as a result.
But what exactly is overfishing, why is it such a big problem - and what can be done about it? Let's dive in.
What Is Overfishing?
Broadly speaking, overfishing is when fish in a particular region are caught at a faster rate than they can repopulate. In theory, this could ultimately lead to the extinction of the species, although in practice, it isn't clear that any fish species is confirmed to have gone extinct solely due to overfishing - although this might soon change, as we'll see.
Overfishing is directly related to the concept of yields. For any fish population, there's an "ideal" amount of fishing that maximizes the number of fish that can be caught in the long-term. Overfishing is simply when the fish in a region are caught at a faster rate than this amount.
"If you don't fish at all, you obviously don't get any long-term catch," Ray Hilborn, professor at the University of Washington's School of Aquatic and Fishery Sciences, tells Sentient. "If you fish too hard, you get very little long-term catch. And in the middle is this theoretical sweet spot that produces what's called 'maximum sustainable yield.'"
Hilborn says that in general, the maximum sustainable yield of a given fish population is "roughly equal to the fraction of fish who would die from natural mortality." For example, if 20 percent of the fish in a certain population would die from natural causes over the course of the year, this implies that fishers shouldn't catch more than 20 percent of that fish over that same period of time.
In contrast, you can look at the overfishing that occurred on Canada's northeast coast throughout the 20th century. Canadian cod was harvested so over-aggressively that by 1992, the region's cod population had fallen to less than one percent of its historic norm.
To ensure the species wasn't wiped out completely, the Canadian government announced a moratorium on cod fishing in the region, a decision that resulted in 30,000 people losing their jobs. And yet, the cod population in the area still hasn't recovered.
Overfishing is often grouped under the larger umbrella of illegal, unreported and unregulated fishing, (or IUU), by scientists, academics and policymakers.
What Are the Consequences of Overfishing?
Overfishing has a number of deleterious environmental impacts. Some of them, like bycatch, are inherent problems with fishing in general that are exacerbated by overfishing practices; others, like trophic cascades, are specifically caused by overfishing.
Ecosystem Destruction Due to Overfishing
Ecosystems involve a complex web of interactions between different species, and in a healthy ecosystem, these interactions naturally balance themselves out in a sustainable way. If predators become too populous, there won't be enough prey to feed them, so some of the predators will die off, which then gives the prey species time to repopulate. This repopulation gives the predators more access to food, thus allowing their species to repopulate, and so the cycle repeats itself.
Overfishing disrupts this natural process, and the consequences can be varied and far-reaching.
Take, for instance, the relationship between parrotfish, coral reefs and algae. Algae thrives in coral, but when it's allowed to grow unchecked, it can damage and kill the coral species. Luckily, parrotfish dine on algae, and so by simply going about their lives, they play an accidental but very important role in maintaining the health of coral reefs.
But when parrotfish are overfished and their population dwindles, this check on algae growth is removed, and the coral reefs suffer. This isn't just hypothetical: A study published in 2015 found that overfishing of parrotfish and other "grazers" has been a primary driver of the steep decline in the health of Caribbean coral reefs over the last 50 years.
This type of phenomenon, in which a change in a predator's population has a downstream effect not only on its own prey but on other species as well, is what's known as a trophic cascade. And overfishing has caused a number of trophic cascades.
The overfishing of sharks on the Atlantic coast led to a collapse in scallop populations, for instance, because sharks eat clownrays and clownrays eat scallops. Overfishing of cod and other sea urchin predators has helped degrade kelp forests, which is an especially big problem given the many environmental benefits that kelp provides.
One of those benefits is the absorption of carbon dioxide from the atmosphere, which brings us to another dire consequence of overfishing: rising global temperatures.
Overfishing Causing Climate Change
The idea that overfishing can exacerbate climate change might sound counterintuitive; after all, what do the number of fish in the sea have to do with the temperature outside? As it turns out, quite a bit.
The ocean absorbs a massive amount of carbon dioxide from the atmosphere: around three billion metric tons every year, or one-third of all global emissions. What's more, the ocean absorbs more carbon than it releases, which makes it a carbon sink - the world's biggest, in fact. Because carbon dioxide is one of the primary greenhouse gasses, the ocean plays an enormous and crucial role in slowing the rise of global temperatures.
But overfishing has diminished the ocean's ability to absorb carbon. That's because ultimately, it's the creatures in the ocean who are sucking up all of this carbon.
The process begins when phytoplankton at the ocean's surface absorb carbon dioxide from the air. These microscopic creatures are then eaten by zooplankton and other larger species, who absorb the phytoplankton's carbon, and so it goes throughout the ocean's food web - all the way up to whales, who can store up to 33 tons of carbon dioxide over the course of their lives.
This is an effective form of carbon storage, because the carbon remains in the ocean and out of Earth's atmosphere even after the fish die - unless, of course, the fish are caught by humans and removed from the ocean, in which case all of that carbon is released back into the air. Overfishing greatly exacerbates this phenomenon: According to a Sentient analysis, overfishing results in an additional 5.6 million metric tons of CO2 being released into the atmosphere every year.
Bycatch Due to Overfishing
Bycatch is what happens when fishers accidentally catch, injure or kill species that they weren't intending to catch. Common victims of bycatch include dolphins, sea turtles and over 200 other species that are protected, endangered or threatened.
The sheer extent of bycatch can't be overstated: It's been estimated that over 40 percent of all fish caught annually are actually bycatch. What's more, bycatch results in the death of more than 650,000 marine mammals - that is, aquatic creatures other than fish - every year.
Hurting Local Fishing Communities
Many coastal communities around the world rely on a healthy supply of local fish to feed themselves. Overfishing and other forms of illegal, unreported and unregulated fishing have hurt these communities in a number of ways, and it's often developing countries that suffer.
In Sierra Leone, for example, overfishing in coastal waters has forced local fishers to travel further and further into the sea to catch fish, exposing them to increasingly dangerous weather conditions. In 2022, Sierra Leonean fishers told the Guardian that they're struggling to feed their families thanks to the dearth of fish caused by overfishing.
Much of the time, the overfishing causing this is carried out by foreign nations. In Japan and South Korea, for instance, more fish is caught by other countries' vessels than by domestic fleets. In Sierra Leone, most of the large trawlers used to harvest fish are owned by European and Asian companies, according to the United Nations, and 40 percent of industrial fishing licenses in the country are owned by Chinese vessels.
Possible Extinction Due to Overfishing
As mentioned earlier, no fish species is confirmed to have gone extinct solely because it was subject to overfishing. But that may not always be the case: A 2021 study by the World Wildlife Foundation concluded that one-third of all shark, ray and chimaera species are currently at risk of going extinct thanks to overfishing.
How Can We Stop Overfishing?
End Harmful Fishing Subsidies
Governments around the world spend a lot of money subsidizing their respective countries' fishing industries. Though some of these subsidies are benign, others have been blamed for incentivizing overfishing and contributing to all of the above problems. For instance, many governments subsidize or discount the fuel for shipping vessels, allowing them to fish longer, harder and farther away.
The world's governments spend over $20 billion on what researchers call "harmful fishing subsidies" every year, according to a 2019 study in the journal Marine Policy. Eliminating, or even substantially reducing, these subsidies would go a long way to curb overfishing, according to a range of experts and marine advocates.
Protect More of the Ocean
Marine Protected Areas (MPAs) are areas of the ocean in which legal protections have been established for conservationist purposes. The nature and degree of these protections vary, but many of them have been effective at reducing or eliminating overfishing within their boundaries.
However, MPAs only cover a miniscule portion of the ocean. According to the UN, less than nine percent of the ocean is protected by MPAs - and that's one of the higher estimates. The Marine Conservation Institute puts the number at around five percent, while a 2024 report by a group of NGOs claimed that, due to lax enforcement and weak protections in some MPAs, only 2.8 percent of the ocean is effectively protected from overfishing.
Regardless of which estimate is most accurate, the upshot is clear: Over 90 percent of the ocean is unprotected. Bolstering MPA enforcement and bringing more of the sea under legal protections - which the UN, to its credit, is currently attempting to do - would be another powerful check against overfishing.
Eat Less Seafood
One factor driving overfishing is that consumers are increasingly developing a voracious appetite for seafood. Some coastal communities are dependent on fish for their diet, but the rest of us can be mindful of overconsumption, and how it impacts wildlife, including fish and other marine life. One alternative: the many sources of plant-based protein that don't exact anywhere near the environmental cost of seafood (or meat, for that matter).
The Bottom Line
Although it has become increasingly popular to think of fish as a sustainable alternative to meat, the far-reaching environmental, animal and human impacts of persistent overfishing throws a wrench into that narrative. If industrial fishing operations continue at their current pace, so will overfishing - at high cost to marine habitats and our ability to stave off the worst effects of global warming.
Seth Millstein wrote this article for Sentient.
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