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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By Leilani Marie Labong for FoodPrint.
Broadcast version by Suzanne Potter for California News Service reporting for the FoodPrint-Public News Service Collaboration.

At a recent pop-up in Healdsburg, California, to preview Chef Jacob Harth's forthcoming sustainable West Coast seafood restaurant, Winnie's, I tasted my first raw, line-caught Pacific sardines. (The tinned version stars in one of my first food memories, so this new experience was long overdue.) Cured in seaweed salt and gently warmed over coals, the dense and oily fish had been reeled in less than 24 hours before from the ocean off San Diego. But since commercial fishing of Pacific sardines was closed in 2015 (the third moratorium implemented since 1967 to rebuild the boom-and-bust population), how in the world did these forage fish end up on my fork?

Turns out, they were caught up in a targeted mackerel harvest and sold as bycatch, defined as "anything that is caught in the fishing process beyond the species and sizes of the targeted marine organisms," according to the Food and Agriculture Organization (FAO) of the United Nations. This definition casts a wide net and includes, for example, ocean sunfish (Mola mola), an unmarketable bycatch of the California swordfish fishery; the 10 orcas accidentally ensnared off Alaska's Aleutian Islands last year by bottom trawlers in pursuit of yellowfin sole and Pacific Ocean perch; and the Pacific sardines at Winnie's, an incidental catch of an otherwise protected, non-target but quite marketable species.

"Anytime you put a hook in the water, you can't be sure what's going to bite," says Dave Rudie, founder of the seafood market Catalina Offshore Products in San Diego. "So inevitably you're going to get some bycatch." Thanks to the active commercial ban on the fishery, the National Oceanic and Atmospheric Association (NOAA) currently considers the Pacific sardine stock "not overfished." So, onto my plate they went.

What is bycatch - and when is it edible?

"There are multiple meanings of bycatch depending on who you talk to," admits Elizabeth Hellmers, a senior environmental specialist with the California Department of Fish and Wildlife (CDFW). "But as long as their populations are healthy and being managed properly, it's beneficial for the entire production pathway [from fishers to consumers] to use as much bycatch as possible."

Domestic bycatch is monitored by the National Marine Fisheries Services and the U.S. Fish and Wildlife Service, with help from heavy-duty legislation like the Marine Mammal Protection Act, the Endangered Species Act, and a host of other legal provisions that aim to keep our sea stocks flourishing. Even though a 2018 assessment by the FAO estimates that bycatch amounts to nearly 10 percent of the global catch, an NOAA review of standardized bycatch reporting acknowledges that some information about bycatch is predictably anecdotal. "It's hard to count fish in or out of the sea," quips Harth.

Eclipsed by more newsworthy bycatch tragedies, the sustainable utilization of bycatch often goes unsung. Adrian Hoffman, cofounder of Bay Area-based Four Star Seafood (a "first receiver" that "lands" fish and shellfish directly from fishermen before distributing it to restaurants and markets), assumes that the average consumer doesn't think about bycatch much. Why would they need to when halibut, salmon and cod - the pelagic mainstays of American gastronomy - are always in ready supply at the grocery store?

"If consumers do think about bycatch," Hoffman says, "their impression of it is probably something like, 'Oh, some people went fishing and caught all this stuff they can't use, so they just threw it back over.'" Evidently, the average consumer of Hoffman's imagination is not far off the mark: conservation nonprofit Oceana reports that approximately 17 to 22 percent of annual U.S. bycatch is "discarded at sea, likely already dead or dying," while in Europe that number is closer to 50 percent, much to the detriment of marine environment.

Since the U.S. imports 62 to 65 percent of its seafood, utilizing bycatch seems like a legitimate strategy - along with, for instance, sustainable stateside aquaculture - to alleviate that burden. Rudie warns of the "transfer effect," or the shift in supply from well-managed U.S. fisheries to foreign fisheries with potentially questionable standards. "It's quite a trade-off," he says forebodingly.

In grassroots fashion, seafood purveyors and chefs are endeavoring to create awareness around utilizing bycatch, which is doubly sustainable if harvested through methods like hooks, harpoons, bottom-set longlines and traps. Slower and more targeted, these methods produce a micro-catch compared to the weighted bottom-trawler nets typically used in industrial fishing operations (which are very restricted, at least on the West Coast). Giant trawlers not only account for 78 percent of global discards, but they also send plumes of carbon dioxide into the atmosphere and contribute significantly to ocean acidification as they sweep the seabed indiscriminately.

Sustainably caught West Coast bycatch can include Pacific octopus and wolf eel from Dungeness crab pots and skate or dogfish from bottom-set longline black cod. "At some point we're going to need to be very familiar with bycatch," says Harth, "because that's all that's going to be left to eat if we keep going after the same old fish."

Advocating for bycatch

With Winnie's opening in summer 2025, and numerous pop-up previews until then, Harth continues his crusade to advance the use of bycatch and other undervalued sea species, a passion that originated while sportfishing with his father near their family home south of Tillamook Bay, Oregon, and commercial fishing for his erstwhile Portland seafood restaurant, Erizo.

Over the course of his lifelong seafaring history, Harth has developed certain insights about bycatch or even underutilized species. For instance, red and brown rock crab, which can be found in great abundance along the West Coast, make a more robust seafood stock compared to the highly sought-after Dungeness, which has a more delicate flavor despite being "stressed out." While lingcod and rockfish are common targets for rod-and-reel fishers casting off jetties in Oregon, the chef also enjoys the mild and flaky flesh of lesser-known cabezon or monkeyface eel that occasionally hook on the same lines. And at hyper-regional Erizo, he eschewed the wild mussels and ocean-farmed oysters from eastern Canada's Prince Edward Island - a frequent fossil fuel-guzzling flex on West Coast restaurant menus - for Oregon's own gooseneck barnacles, littleneck clams and surftide mussels, which more meaningfully evoked sense of place.

"If anyone could influence someone's opinion about bycatch species, it might be a chef or a restaurant," says Harth. Indeed, he is the latest in a legacy of toques who have fought food waste with kitchen initiatives; consider Dan Barber's WastEd series, which turned food scraps into delicious dishes like fried skate-wing cartilage and beet-pulp burgers, and Massimo Bottura's Food for Soul program, which feeds the homeless warm and nutritious meals made from high-quality restaurant discards. As Katherine Miller, author of "At the Table: The Chef's Guide to Advocacy," said in an interview with The Bittman Project, "Chefs are well suited to help accelerate advocacy work. They can help translate complicated topics into something easier to understand. [They] have too much influence on our food choices ... to just sit on the side lines."

Harth's advocacy brings attention to a waterfall of lost resources and opportunities - the hallmarks of a broken food system - associated with blindly jettisoned legal bycatch, which include but aren't limited to a recreational fisherman's missed meal, the massive carbon demand of importing seafood from foreign countries, and the overfishing of popular species. His activism also manifests in a respectful, elevated approach to preparing these so-called discards: In his purview, house-made butter is flavored with smoked Kellet's whelks, a bycatch of Santa Barbara's lobster fishery. Of the Pacific octopus often found in crab pots, he makes wood-grilled skewers slicked in wild mushroom oil. (Doing their part for the survival of the species, Pacific octopus spawn hundreds of thousands of eggs and die soon after, often at the claws of crabs, which is why they're regularly found in the pots.) And turning purple sea urchin into uni-on-toast is especially beneficial, since the urchin is an invasive species with a voracious appetite for the valuable kelp forests along the Mendocino Coast.

But if mild white fish is the extent of your seafood palate (no judgment here), Harth assures that wolf eel and the small shark species dogfish - whose low marketability in the U.S. may be due to their canine-related monikers among other stigmas - will readily appeal. What's considered bycatch in America may be target catch elsewhere in the world, theoretical proof of concept for their culinary applications. In Ensenada, Mexico, dogfish and angel shark are the preferred proteins for Baja-style fish tacos - a nod to the 1950s and '60s Japanese fishermen who introduced their traditional tempura-battered shark to the region. "That's part of the appeal of most bycatch," says Harth. "It's different, but also familiar."

Marketing for sustainability

Also fighting current on the way to marketability is opah, the world's only fully warm-blooded fish species, a biological advantage that helps them swim, digest and react faster than their cold-blooded cohorts in cold, deep ocean. Its flesh may have a beautiful pinkish-orange hue reminiscent of tuna, but some of its cuts, particularly the adductor muscle, taste entirely, well, beefy. And flavor hasn't been the only barrier to more widespread inclusion on the American dinner table: Its appearance is also unusual. Opah looks almost celestial, with gold-rimmed eyes and a full moon-shaped body that's speckled, silvery and rosy around the edges. For some, the fish may look too otherworldly to eat.

In 2013, Dave Rudie of Catalina Offshore Products received a call from fishermen who were harvesting Pacific bluefin tuna between Hawaii and California. They had found the target species in high numbers, though a significant fraction of the catch comprised opah. Still, Rudie agreed to purchase their 30,000-pound harvest, and subsequent monthly deliveries thereafter, to reboot the tuna supply in San Diego specifically for the sushi market. The city's once-booming tuna canneries ceased operations in the 1970s and '80s, parallel to the decline of Pacific bluefin and yellowfin species in the area due to overfishing.

"But opah was not a popular fish," Rudie says, "so we had to figure out how to sell it." He applied for, and received, NOAA's Saltonstall-Kennedy Grant, which funds efforts to "help fishing communities optimize economic benefits by building and maintaining sustainable fisheries." Catalina Offshore began working with the Southwest Fisheries Sciences Center to find ways to promote the fish using social media, retail sales and local chefs' innovative recipes, such as opah burgers and opah pastrami.

Their marketing savvy paid off. But just as demand for the fish began to rise, the amount of opah bycatch began to trough. "Good old supply and demand," muses Rudie, who sold Catalina Offshore about a year ago and has since pivoted to promoting yet another misunderstood species, the aforementioned purple sea urchin. "That's the free-world capitalist system for you."

Bycatch for the future

The latest Fisheries Economics of the United States Report, from 2022, revealed that the U.S. commercial and recreational saltwater fishing industry generated $321 billion in sales and supported 2.3 million jobs. Climate activist Ian Angus traces the origins of capitalism back 5,000 years to when "fishing for sale rather than consumption developed with the emergence of class-divided urban societies." Additionally, he cites the first mention of overfishing in texts dating back nearly 2,000 years, when the Roman poet Juvenal lamented having to import fish from Corsica and Sicily because "our waters are already / Quite fished-out, totally exhausted by raging gluttony." Sounds like overfishing, or the depletion of fish stocks due to a faster rate of harvest compared to the natural tempo of renewal, is a tale as old as time.

Can utilizing bycatch tackle such an ancestral problem? Maybe not entirely, but Hellmers of the CDFW thinks that using less-popular species can at least take "a little bit of pressure" off the main ones. "We have a huge demand for seafood in this country, so anything that can be used and sold is beneficial for the fishers, the consumer, and from a management perspective," she says.

If the importance of utilizing bycatch isn't obvious by now, consider the fact that such familiar fins of American eating - like petrale sole, ocean perch and Chinook salmon - are among the 30 species presently considered threatened and endangered from overfishing, dams and pollution in the California Current, an oceanic current and dynamic ecosystem that flows from southern British Columbia, Canada, to southern Baja California, Mexico. In 2018, the fall-run Chinook that historically spawn in the Klamath and Sacramento Rivers were determined overfished; in 2023, the fisheries were "declared a disaster" by California's secretary of commerce. Even though Chinook and other salmon runs like coho have been in decline for decades, California has only canceled the last two salmon seasons. Currently considered non-legal bycatch in the Golden State, captured salmon must be released back to the waters from whence they came.

But perhaps the proverbial tides are turning. Earlier this year, dams along the Klamath, a major California-Oregon watershed, were removed and salmon have since been spotted in reaches of the river formerly unreachable for more than a century. Despite the potential to appeal to a wider audience once salmon fishing comes back online, Harth plans to stay the bycatch course. "There will need to be many, many more improved seasons for me to even consider putting salmon on my menu," says Harth. And likely no shortage of bycatch to fill the void.


Leilani Marie Labong wrote this article for FoodPrint.


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By Sophie Kevany for Sentient.
Broadcast version by Suzanne Potter for California News Service reporting for the Sentient-Public News Service Collaboration

Fish, once a Friday penance for many, has recently become the "good meat" poster child. Fish farming has been touted as a way to help protect wild marine animals and, by some, even a way to feed the world. Yet a new study in Science Advances makes the case that farming fish comes at a much higher cost than previous estimates suggest, because of how much aquaculture relies on wild fish. According to the researchers, the total mass of wild fish required to produce farmed fish could be 536 percent higher than previous estimates. The drain on wild fish populations can in turn make it harder for vulnerable communities to find food. One of the core arguments for farmed fish - the idea that it protects wild fish by leaving them in the sea - ignores the fact that aquaculture relies on feed made from wild anchovies, sardines, herring, mackerel and other fish that many coastal nations rely on for sustenance.

The field of fish farming is no stranger to criticisms: overcrowded pens; poor fish health; inhumane killing methods; pollution; plastic waste from nets used to create pens, as well as diseases (spread by escaped farmed fish) that cause health problems for wild fish populations.

Nonetheless, the practice is growing. Farmed fish production is expected to have expanded by over 17 percent between 2022 and 2032, according to the United Nations Food and Agriculture Organization. By 2050, global demand for fish is expected to nearly double, thanks in part to an ever-increasing output of farmed seafood. Over a similar period, demand for fishmeal - the feed carnivorous farmed fish like salmon, trout and bass rely on - is projected to grow over seven percent by 2030.

"This is a hot topic in academic circles, but I don't think the public understands how fish farming works, especially in terms of its reliance on wild fish," Spencer Roberts, an environmental science and policy researcher at the University of Miami and a co-author of the new study, tells Sentient. In reality, says Roberts, aquaculture has simply shifted pressure from one set of fish to another.

The need for fish feed is creating problems for people too. "When we hear about fish farming feeding the world, it's not true. The reality is that it's starving people...in places like West Africa where 'reduction fisheries' are taking their fish," says Roberts, and selling or using them to turn into fishmeal. "Subsistence fishing communities are literally starving and being forced to emigrate," Roberts adds.

Part of how the aquaculture industry sold itself as the more sustainable option is thanks to what's known as the fish-in-fish-out ratio - the measurement of how many wild fish it takes to feed farmed ones. This figure, in essence, compares the number of how many wild fish are used as feed for fish farming, versus how many come out to feed humans. The calculation is used by the industry to demonstrate its efficiency, and therefore, its sustainability. It's used to make the case for how large a role it should play in a future with a growing global population, increasing planetary warming and shrinking natural resources, like farmland to grow food.

By focusing only on the ratio, Roberts and his co-authors argue, the true number of wild fish used to feed farm ones ends up obscured - indirect deaths are ignored, essentially - while outputs are maximized. This creates a misleading measurement.

There are a number of ways this plays out, but here's one example: so-called fish trimmings. Trimmings, which are the parts of the fish people don't traditionally eat (heads, tails and so on), are conventionally classified as by-products and subtracted on the basis that they are not wild fish. But according to a representative from The Marine Ingredients Organizations, only about 20 percent of trimmings for fishmeal come from farmed fish. The other 80 percent is from wild fish.

Once you adjust the calculation for the fish trimmings and other factors, the study finds, the volume of wild fish used to feed farmed fish could be over 300 percent higher than standard estimates. Taking other factors into account - when farmed fish that don't eat fishmeal are excluded, and indirect mortalities like slippage are included - it's even more dramatic. The total wild fish mass, according to the study, could be 536 percent higher.

It is not yet possible to convert the study's new percentage estimates into wild fish numbers, but Roberts says researchers working on the question believe reduction fisheries account for most fish taken from the ocean each year, killing over a trillion wild animals. These are animals who could otherwise be maintaining ocean health simply by staying in the sea, or helping to feed vulnerable populations.

Responses from fishmeal trade bodies to the new study varied, with the Marine Ingredients Organization favoring "a shared metric system" of lifecycle assessments, rather than fish-in-fish-out, and linking to a study that supports these as "the pathway to improved sustainability for all feed ingredients." A life cycle assessment quantifies the environmental impacts of a product, system or service from beginning to end.

The Federation of European Aquaculture Producers' general secretary Javier Ojeda was more upbeat about the study, saying its average ratio confirms that farming of fish reliant on fishmeal "is a net producer of aquatic food [which] should be heralded as great news," rather than a way to "demonize" it.

The Problem with Dewilding the Ocean

Fish farming creates another problem: dewilding. Separately, another new study finds mariculture - fish farming that takes place in the sea - is contributing to oceanic dewilding. Dewilding is a term for prioritizing human interests over ecosystems and, essentially, destroying the natural or wild world. Fish farms pollute the ocean too, with fish feces and uneaten food from farms creating excess nitrogen and phosphorus that can lead to algae blooms, depriving the water of oxygen.

The study looks at different dewilding categories, one of which is conceptual dewilding. Conceptual dewilding is a category that deals with human perceptions, which can set the stage for uncontrolled exploitation, says Becca Franks, co-author and assistant professor of environmental studies at New York University.

"The ocean is less explored than the moon... [but] as we map it for more places to put farms in and start to see it as a place to extract more resources from, the less we see it as a wild place, and the more we are going to be casual about destroying it," Franks tells Sentient.

Findings by Roberts and his team that aquaculture's dependence on wild fish is underestimated, are, Franks says, an example of "this rough, casual" approach to marine environments, and evidence that we are "not looking at the ocean as a wild space that should be approached with respect and caution."

Franks offers an example of humanity turning from a rough approach to a respectful one: whales. "We used to see them as floating oil reserves ...[but] with enough organizing and attention to who they actually were ... and allowing a bit of poetry to come in ... [we have] completely changed the way we think about whales, and it has allowed them to do better."

The bottom line, according to Franks, is that the critical role of oceans in storing carbon and mitigating climate change means we should take a very careful look at what kinds of aquaculture we want to proceed with, adding, "the details really matter."


Sophie Kevany wrote this article for Sentient.


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Scientists are sounding the alarm about growing dead zones in the Gulf of Mexico and beyond.

Dead zones are areas of water with hypoxia, or dangerously low levels of oxygen. Dead zones are caused by pollution, including fertilizer runoff from factory farms. The nutrients cause algal blooms which sink and decompose, and the process consumes oxygen on the ocean floor.

With this comes stratification, where differences in temperature among other factors prevent bottom waters from mixing with the oxygenated surface waters. Most species cannot survive long within a dead zone.

David Scheurer, oceanographer for the National Oceanic and Atmospheric Administration, said even short-term exposure can have effects.

"Hypoxia can have impacts on organisms, what we call sublethal impacts," Scheurer explained. "Instead of an outright fish kill, they can affect the development of fish and that can affect the ratio of males and females in the population, the fecundity of the species. That can eventually translate into larger population effects down the line."

This year's hypoxic zone in the Gulf was larger than forecast, at more than 6,700 square miles.

The Gulf dead zone is the largest in the country and the second-largest in the world. It forms every year and can vary in size. This year's dead zone far exceeds the 1,900 square-mile goal set by the Gulf of Mexico Hypoxia Task Force, a collaborative state and federal partnership.

Dead zones do not only threaten marine species such as shrimp and fish. They also upset local economies and imperil already fragile coastal communities living along the Gulf.

Scheurer pointed out climate change is likely to make the problem worse.

"Water holds less oxygen when it's warmer, organisms use more energy when it's warmer," Scheurer noted. "You also have the potential for enhanced stratification due to the temperature, as well as potentially increased nutrient inputs if climate change causes more rainfall in the watershed. "

The record 8,700-mile dead zone of 2017 reduced the brown shrimp habitat by 25%. In Louisiana and Texas, wild-caught shrimp landings are on a downward long-term trend, with historic lows in recent years.

Nutrient pollution goals set by the task force are voluntary and without enforceable state or federal limits, advocates stressed success will remain elusive.

This story is based on original reporting by Marlena Williams for Sentient.


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