MONTEREY, Calif. -- Kelp forests off the West Coast are being decimated at an alarming rate by marine heat waves linked to climate change, according to seven top marine scientists who just wrote an open letter about it that was published in Science magazine.

Fiorenza Micheli, a professor of marine science at Stanford University and co-director of the school's Center for Ocean Solutions, said kelp forests are a sentinel for the health of the oceans.

"We are seeing change that is happening very rapidly and on a very large scale," she said, "and it's affecting this ecosystem -- and very little is being done."

Studies have predicted that unless the world stops dumping increasing amounts of CO2 into the atmosphere, marine heat waves will become the "new normal" by the end of this century. Micheli called for better monitoring and more research to identify heat-resistant types of kelp that can be used for restoration.

Off the coast of Northern California, 90% of kelp has died off in the past five years, which threatens many species of commercially important fish. Micheli said she believes the United States must join other countries to tackle climate change, the ultimate driver of this problem.

"Global action in addressing the ultimate cause of this problem -- that is the most important part of this," she said. "Everything else is really just a way of buying some time."

She said California, Oregon and Washington state need to coordinate efforts to restore damaged kelp forests, remove some of the sea urchins that are overfeeding on the kelp, and protect otters and other species that prey on sea urchins.

The letter is online at science.sciencemag.org.

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Support for this reporting was provided by The Pew Charitable Trusts.


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Conservation groups, including the National Wildlife Federation and Oceana, are calling for a moratorium on deep-sea mining for minerals until more research can be done on the potential environmental risks.

President Donald Trump recently signed an executive order fast-tracking seabed mining. His goal is to boost the nation's stockpile of minerals like lithium, cobalt and nickel used in cellphones, solar panels and long-storage batteries.

Geoff Shester, California campaign director and senior scientist for the advocacy organization Oceana, said it would be tragic to strip-mine the seafloor without regulations to mitigate the harm.

"You could essentially be eliminating huge ecosystems without even understanding what was there in the first place," Shester pointed out. "And without any possibility that these ecosystems can recover for centuries."

In 2022, California banned seabed mining in state waters. The International Seabed Authority has yet to pass meaningful restrictions and has already authorized some test mining in an area of the Pacific rich in polymetallic nodules, called the Clarion Clipperton zone.

The Trump administration has called deep-sea mining a "core national security interest," saying it cannot rely on foreign sources to supply the minerals. Shester thinks the U.S. government should take a more cautious approach.

"With the current administration's approach, there's really no recognition of the value of these ecosystems and the services they provide," Shester argued. "It's really about, 'How much money can be made in the short term to enrich the pockets of these large corporations?'"

He added deep-sea research has the potential to help cure disease and uncover genetic information that could help scientists understand the history of life on Earth.


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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.

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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