Overfishing has caused cod to halve in body size since 1990s, study finds
Overfishing has led to a collapse in the eastern Baltic cod population, but over the past three decades the size of the fish themselves has also been dramatically and mysteriously shrinking.
Now scientists have uncovered genomic evidence that intensive fishing has driven rapid evolutionary changes that have contributed to these fish roughly halving in average body length since the 1990s.
The 'shrinking' of cod, from a median mature body length of 40cm in 1996 to 20cm in 2019, has a genetic basis and human activities have left a profound mark on the population's DNA, the study concluded.
'When the largest individuals are consistently removed from the population over many years, smaller, faster-maturing fish gain an evolutionary advantage,' said Prof Thorsten Reusch, head of the marine ecology research division at Geomar Helmholtz Centre for Ocean Research Kiel and senior author of the research.
'What we are observing is evolution in action, driven by human activity. This is scientifically fascinating, but ecologically deeply concerning.'
The dramatic shrinking of cod has been a source of concern for several decades, but it was not clear to what extent the phenomenon has been driven by environmental factors such as hypoxic conditions caused by algal blooms, pollution and more extreme marine seasonal temperature changes.
'It was very hard to prove that it was an evolution that had happened,' said Dr Kwi Young Han, first author of the study, who completed her PhD at Geomar.
The study used an archive of tiny ear bones, called otoliths, of 152 cod, caught in the Bornholm Basin between 1996 and 2019. Otoliths – a bit like tree rings – record annual growth, making them valuable biological timekeepers.
The scientists combined annual growth data with the cods' body size metrics and genetics to assess whether there had been a genetic shift in the population over 25 years under fishing pressure.
Between 1996 and 2019, the median length of a mature cod in the dataset fell from 40cm to 20cm. The median weight in 2019 (272 grams) was just a fifth of the median weight of a mature cod caught in 1996 (1,356 grams).
The analysis revealed systematic differences between fast- and slow-growing fish and that the gene variants that make a large body size more likely have become less common over time, indicating an evolutionary pressure.
Trawling is intended to be size selective, with legally binding minimal mesh sizes designed to protect smaller individuals and allow fish to reach maturity and spawn before being caught.
However, this may have had the unintended consequence of producing a strong selective evolutionary pressure in favour of smaller fish, which would be more likely to escape the nets.
'The demographic argument is that each individual should at least reproduce once before being caught,' said Reusch. 'While this seems logical in terms of keeping a healthy demography of fish stocks, it has the potential to totally mess up the genetic and size structure.'
The findings, published in the journal Science Advances, could help explain why there has been no rebound in the body size since the collapse of the stock prompted a complete fishing ban of eastern Baltic cod in 2019, which remains in place.
Prof Stefano Mariani, a marine biologist at Liverpool John Moores University, who was not involved in the research, said the genetic analysis could not explain the full extent of the shrinking that has been observed, with environmental factors probably also playing a significant role.
But he said showing that 'the activities of humans can speed up evolution' was a 'milestone' result that highlights the importance of monitoring the gene pool of fish populations, as well as simply tracking numbers of fish.
'It would be really good to try to maintain diversity because as soon as you chop away a certain section of diversity, it's like losing an insurance for the future where that might have an advantage,' he said.
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National Observer
7 days ago
- National Observer
How Copenhagen is adapting to a wetter future
This story was originally published by Yale Environment 360 and appears here as part of the Climate Desk collaboration In just two hours on July 2, 2011, a torrential, once-in-a-millennium storm battered and flooded Copenhagen, pounding parts of Denmark's capital with more than 5 inches of rain. Critical infrastructure at the city's largest hospital was swamped, as were major roads, basements and businesses. The city that had been engaged with advanced sustainability planning for decades, it turned out, was woefully unprepared for the fierce rainfall, which caused $1.8 billion in damages. Shaken by the calamity, the city and its citizens grasped that such climate disasters — and deluges even more severe — were inevitable and required a rapid and strong response. To that end, Copenhagen brought together its top urban planners, landscapers, consultants, and architects to turn the city, which stretches across two main islands in the Baltic Sea, into the world's first full-fledged ' sponge city.' This state-of-the-art defense system — which combines nature-based surface features, like wetlands and parks, with large underground structures, like storage pipes and retention basins — is expected to fortify the city against cloudbursts and sea level rise for 100 years. The intricately designed network manages stormwater and rising tides by soaking them up, storing them, and then slowly returning water to the water cycle. The sponge city build-out has been so successful that cities as disparate as Auckland, Nairobi, Singapore, New York, Rotterdam, and Berlin — and many others in the U.S. and Europe — now consider it an example to emulate. 'Even though the Chinese were first and coined the term sponge city,' explains Maryam Naghibi, an urban landscape architect at Delft University of Technology, in the Netherlands, 'Copenhagen is a model for cities everywhere with such dense urban fabric.' The Intergovernmental Panel on Climate Change predicts that urban centers in high latitudes will experience both heavier and more frequent rain events in future decades, with 100-year flood events at least doubling in frequency across 40 percent of the globe by 2050, according to a 2024 paper published in Nature. Moreover, the melting of polar ice sheets will cause sea levels to rise — an obvious threat to low-lying, sea-bound Denmark. The Danish Meteorological Institute predicts as much as 55 percent more precipitation in the winter months by 2100, with downpours ever more intense, should global temperatures rise by 2 to 3 degrees Celsius over preindustrial levels. Denmark's adjacent seas — the North and the Baltic — could rise by up to 4 feet. 'We have projections on how the city is going to look and where the climate crisis will be,' says Christian Nyerup Nielsen, the global director for climate adaptation at Ramboll, a consulting firm that helped develop climate adaption masterplans for several areas of Copenhagen. 'We have to anticipate the extreme weather events a century from now.' In the face of more and fiercer storms and rising sea levels, Denmark's capital is enacting an ambitious plan to build hundreds of nature-based and engineered projects to soak up, store, and redistribute future floods. A year after Copenhagen's 2011 flood, planners unveiled the Cloudburst Management Plan, a comprehensive citywide blueprint to revamp the city's defenses against heavy rainfall and storm surge and offer some protection against drought as well. Today, hundreds of flood-mitigation projects blanket the city, with hundreds more in the works. Some are massive, like subterranean pipelines roughly 10 feet in diameter that convey stormwater to treatments plants and then to the harbor. Others are more unassuming, including bioswales (vegetated depressions that retain and filter stormwater), pocket gardens, and 'sponge parks,' which combine green roofs, permeable pavement, and water-absorbing plants. Although the Cloudburst project, which was originally slated to be completed in 2032, is less than halfway to its goal, experts say that Copenhagen is already in significantly better shape to withstand torrential rains. According to Naghibi, the city's flood risk has been reduced by 30 to 50 percent in high-priority areas. The sprawling array of completed projects includes both 'blue-green' and 'gray' innovations. The former reflect a nature-based approach: Green spaces like parks and gardens filter and retain stormwater; trees and other plants suck up water; open spaces, like lawns and meadows, allow infiltration; streams with revegetated banks that have been freed from underground pipes (a process called daylighting) spread out and retain stormwater; lakes that have been enlarged and ringed with wetlands increase water storage capacity. Likewise, green roofs and façades absorb rainwater — while freshening city air. The city also replaced impermeable pavement on roads, parking lots, and in public squares with permeable materials that enable them to drain more efficiently. Complementing the surface modifications, Copenhagen also employs gray, or engineered, solutions to receive the overflow from parks and streets, store it, and — in times of extreme rainfall — release it directly into Copenhagen Harbor. This network includes mile-long underground tunnels, subterranean basins, pumping stations, and enlarged sewage pipes, which convey both sewage and stormwater. Among Cloudburst's flagship projects, perhaps none is more eye-popping than Karen Blixens Square, one of the city's largest public spaces, on the University of Copenhagen's southern campus. The nearly five-acre expanse of undulating cast-concrete domes and oval pocket gardens functions as a gathering space for students and the public, an event arena, and a catchment for rainwater. In the event of extreme precipitation, the depressions under the mogul-like 'bicycle hills' — which shelter more than 2,000 bikes — retain stormwater, thus taking pressure off the nearby canal. Throughout the square, planted garden beds also absorb water, promote evapotranspiration, and provide habitat for insects, birds, and wildflowers. 'Copenhagen's adaption efforts aren't just technical and functional, but they're social too,' says Naghibi. 'The infrastructure is aesthetically pleasing and experiential, like collection basins that are also skate parks and amphitheaters.' Moreover, she says, the city's design solutions 'offer co-benefits like shade, biodiversity, and urban cooling.' In contrast, she says, China's sponge city initiative is a broader, national program with a stronger emphasis on large-scale infrastructure. It aims not only to manage runoff, but also to conserve water and improve water quality across numerous cities. Across the harbor from Karen Blixens Square lies historic Enghave Park, a roughly 11-acre swath divided into lawns, gardens, playgrounds, and ball fields. It took three years to redesign and physically lower the park, which now includes an integrated underground reservoir with a capacity of close to 6 million gallons. Concrete retaining walls guide rainwater into the park and increase its water storage capacity by an additional 3.7 million gallons. When the walls aren't in the service of flood prevention, park visitors can sit on them. Copenhagen's water utility, HOFOR, is responsible for the four subterranean tunnels, or 'water highways,' that form the backbone of the city's new underground network. The two completed tunnels were expensive — a total of $98 million — but they were designed to handle the torrential downpours expected over the next century. Another tunnel is in progress, and the final one is scheduled to begin construction next year. Copenhagen's 2012 blueprint was significantly bluer and greener than gray, says Ramboll's Nyerup Nielsen. But this has gradually shifted. 'The plan was to have almost everything aboveground, but now there's more beneath-the-earth construction than we envisioned. This is partly because when you really need to move fast you tend to fall back on what you have done before.' Gray infrastructure can handle significantly greater volumes of water than smaller-scale green modifications, he says. Copenhagen's learning curve has been steep. 'Because many pieces of the city are interlocking, when you change one thing it affects something else,' says city planner Jonathan Reghev, referring to the existing underground systems for energy, drinking water, and communications. For example, the plan to regrade city streets, turning them into 'cloudburst roads' that funnel water into city parks, faltered because of the immovable water mains and electrical cabling beneath them. 'It's a massive engineering challenge, and there's no end date now,' he says, referring to the original projection for completion. The quality of the water in the tunnels has presented another aggravation. There's disagreement about how clean the runoff must be to flow into the harbor and freshwater ponds, says Reghev. 'Some runoff will have to go back to the sewage treatment plants first. We didn't know about microplastics and forever chemicals back when we began this. This has caused clashes between environmental protection norms and the adaptation planning.' Northern Europe is currently suffering from severe drought, another consequence of the climate crisis. Denmark's drought index has been above 9 (on a scale of 1 to 10) since mid-May. Although Copenhagen's architects say that urban flooding is the city's foremost concern, the sponge city model offers advantages in times of aridity, too. The city's green spaces, which detain water, help to replenish the city's aquifers, and its tunnels, which hold rainwater from moderate-size storms, function as reservoirs that can be tapped during dry spells. 'This is one reason the tunnels are so big,' says Liam Blunt, a sustainable urban planning expert at Lund University in Sweden. 'The extra size of the pipes is for storage.' Mostly, though, the broader, long-term benefits of Copenhagen's adaptation initiatives have yet to be realized. At the onset of the Cloudburst program in 2012, the city had stated plainly: 'Until the full system is in place, Copenhagen remains vulnerable.' Experts and developers say that the city's progress thus far is impressive, and worthy of emulation. But they also acknowledge that Copenhagen still couldn't handle a tempest like the one that hit it in 2011.
National Observer
01-08-2025
- National Observer
AI observers hit the high seas
This story was originally published by bioGraphic and appears here as part of the Climate Desk collaboration Accurately monitoring a fishery — knowing how many and which fish species are being caught, and what misfortunate creatures are being dragged in as bycatch along the way — has never been easy. Around the world, the job of keeping tabs on fishers has typically fallen to people called fisheries observers who temporarily join a fishing crew to watch and record. There to take scientific observations and report any rule breaking, these independent monitors often have a difficult and dangerous job. Harassment and unsafe working conditions are common, and violence can be rife. Every year since 2009, at least one fisheries observer has gone missing at sea. In other words, relying on onboard human observers is a notoriously imperfect way to regulate fishing activity. Slightly easier and cheaper, and decidedly much safer, is fitting fishing vessels with cameras that record their catches. But even video review is costly and time-consuming. A single fishing trip can generate hundreds of hours of video footage that someone still has to comb through to identify and count the animals flying past the camera. For small-scale fishers, like those involving Indigenous communities on the west coast of Canada, video monitoring and review can be even more of a burden. Though monitoring is essential for managing fish stocks, the Canadian government's fisheries monitoring system was designed with large, commercial, single-species fishers in mind, says Lauren Dean, a communications specialist for the Ha'oom Fisheries Society, an Indigenous organization representing five First Nations near Tofino, British Columbia. Unlike regular commercial fishers, however, Ha'oom's fishers often embark on relatively modest expeditions targeting several species at once. In the Canadian government's view, each species targeted counts as a different commercial with its own legal monitoring requirements. 'Dealing with five or six different systems for monitoring is simply not viable economically,' Dean says. In recent years, though, a solution has emerged to make fisheries monitoring more accessible, more efficient and safer: artificial intelligence. As machine learning, image recognition and other forms of artificial intelligence grow ever more potent, a startup based in Vancouver and called OnDeck AI is developing a computerized fisheries monitoring system that could radically change the video review process for Ha'oom's fishers and others. Though the system is still in the design and testing stages, OnDeck AI hopes to one day be able to automatically detect and count fish in video footage, streamlining the monitoring process. It has big implications for everything from fisheries management and conservation to Indigenous nations' access to data about their waters and resources. Relying on onboard human observers is a notoriously imperfect way to regulate fishing activity, which is why some are trying to develop artificial intelligence that can aid in the completion of the task — or do it without the need for humans. OnDeck AI is the brainchild of Alexander Dungate, who grew up recreationally catching prawns, crab and sole with his family on the BC coast. In 2021, while studying computer science and biology at the University of British Columbia (UBC), he learned about the world of fisheries monitoring — including the hazardous, sometimes lethal situations faced by independent monitors. He also learned that the archive of fisheries catch footage that has already been amassed is so massive that fully analyzing all of it is nearly impossible. Across the border in the United States, for instance, the Pacific States Marine Fisheries Commission, which helps regulate fisheries in California, Oregon, Washington, Idaho and Alaska, has a year-and-a-half worth of video piled up awaiting review. Dungate reached out to friend and fellow UBC student Sepand Dyanatkar, who was studying machine learning, a branch of AI that focuses on developing algorithms that can learn to analyze data without explicit programming. Building on an AI concept called 'master object tracking,' the pair developed a computer program capable of visually identifying an object — in this case a fish — as it moves through a video. Previous efforts to use AI to audit fisheries catch footage have typically run into the same two types of challenges. One is the generalizability problem. Whether it's turbulent weather, bad lighting, waves and spray splashing the camera or the boat itself getting tossed around in a storm, the qualities of videos captured at sea are highly variable, making analysis difficult. Problem two is the data problem. It takes a significant amount of time and effort to annotate the images and videos needed to train an AI model to pick an individual fish out of an endless barrage of footage, let alone recognize the species. What's more, training a typical AI system to recognize all the rare species — which are often the most important given their ecological significance — is simply not possible, says Dungate, since there just isn't enough footage to work from. For instance, if a killer whale accidentally gets caught in a fisher's net, 'we really need to be able to recognize that. But there's maybe three photos on Earth of that happening,' Dungate says. OnDeck AI sidesteps those issues by designing their system to bypass the need for labeled training data by giving the model the ability to recognize what it's seeing across any setting, including with footage of varying quality captured by different types of cameras in changing weather. Dungate likens the difference between traditional AI models and OnDeck AI's to the difference between memorizing the answers to a test and using more complex reasoning to figure out the answers. In other words, it's being able to identify a fish based on its coloring, shape, and fin structure — even if the system has never seen it before. That's the long-term objective, at least. But for now, OnDeck AI's model needs more priming. So last summer, the company trained its AI system on Ha'oom's video footage. To do that, Jessica Edwards, a Ha'oom biologist, analyzed catch footage alongside the AI. If the model failed to recognize a particular fish in the video feed, Edwards would draw a box around the overlooked animal to teach the algorithm. The goal, Edwards says, is to get the AI system to do as good a job as a human — or better — but in less time. Even before getting to that point, the AI can help an auditor do their job faster by identifying when a fish appears in the footage, allowing them to skip forward to relevant segments of the video rather than having to go through the whole feed. While OnDeck's AI system still needs more tuning, scientists and engineers elsewhere are also trying to crack the AI fisheries observer problem. Some, like a team in Australia, are developing an AI system capable of distinguishing between 12 different species in video footage. Working with the Australian longline tuna and billfish fishers, their system picks the right species roughly 90 per cent of the time. Bubba Cook, the policy director for Sharks Pacific, a New Zealand-based NGO, believes AI-driven monitoring could dramatically increase how much of the world's oceans are under some sort of surveillance. Only a small fraction of the world's fisheries — roughly two per cent — are currently monitored by observers, meaning the vast majority of fishing activity, including the bycatch of protected species, happens without oversight. Though human observers will still be necessary for things like tissue sampling, 'the reality is,' says Cook, that 'electronic monitoring coupled with AI review is the only way we're going to get the level of observer coverage we need.'
National Observer
17-07-2025
- National Observer
New study surfaces explosive risk hidden beneath Antarctic ice
This story was originally published by The Guardian and appears here as part of the Climate Desk collaboration The melting of glaciers and ice caps by the climate crisis could unleash a barrage of explosive volcanic eruptions, a study suggests. The loss of ice releases the pressure on underground magma chambers and makes eruptions more likely. This process has been seen in Iceland, an unusual island that sits on a mid-ocean tectonic plate boundary. But the research in Chile is one of the first studies to show a surge in volcanism on a continent in the past, after the last ice age ended. Global heating caused by the burning of fossil fuels is now melting ice caps and glaciers across the world. The biggest risk of a resurgence of volcanic eruptions is in west Antarctica, the researchers said, where at least 100 volcanoes lie under the thick ice. This ice is very likely to be lost in the coming decades and centuries as the world warms. Volcanic eruptions can cool the planet temporarily by shooting sunlight-reflecting particles into the atmosphere. However, sustained eruptions would pump significant greenhouse gases into the atmosphere, including carbon dioxide and methane. This would further heat the planet and potentially create a vicious circle, in which rising temperatures melt ice that leads to further eruptions and more global heating. Pablo Moreno-Yaeger, at the University of Wisconsin-Madison, US, who led the research, said: 'As glaciers retreat due to climate change, our findings suggest these volcanoes go on to erupt more frequently and more explosively.' The research, which was presented at the Goldschmidt geochemistry conference in Prague, and is in the final stages of review with an academic journal, involved camping high in the Andes, among active and dormant volcanoes. As ice caps and glaciers melt, the pressure they put on volcanoes is released — and the magma that has built up beneath them is more likely to erupt, leading to a vicious circle of heating. Detailed work on one volcano, called Mocho-Choshuenco, used radioisotope dating to estimate the age of volcanic rocks produced before, during and after the last ice age, when the 1,500-metre-thick Patagonian ice sheet covered the area. Analysis of the minerals in the rocks also revealed the depth and temperature at which the rocks formed. This data revealed that thick ice cover had suppressed the volume of eruptions between 26,000 and 18,000 years ago, allowing a large reservoir of magma to build up 10-15km (6.2-9.3 miles) below the surface. After the ice melted, from about 13,000 years ago, the pressure on the magma chamber was released, gasses in the liquid or molten rock expanded and explosive eruptions followed. 'We found that following deglaciation, the volcano starts to erupt way more, and also changes composition,' said Moreno-Yaeger. The composition changed as the magma melted crustal rocks while eruptions were suppressed. This made the molten rock more viscous and more explosive on eruption. 'Our study suggests this phenomenon isn't limited to Iceland, where increased volcanicity has been observed, but could also occur in Antarctica,' he said. 'Other continental regions, like parts of North America, New Zealand and Russia, also now warrant closer scientific attention.' Previous research has shown volcanic activity increased globally by two to six times after the last ice age, but the Chilean study was one of the first to show how this happened. A similar phenomenon was reported via the analysis of rocks in eastern California in 2004. A recent review by scientists found there had been relatively little study on how the climate crisis had been affecting volcanic activity. They said more research was 'critically important' in order to be better prepared for the damage caused by volcanic eruptions to people and their livelihoods and for possible climate-volcano feedback loops that could amplify the climate crisis. For example, more extreme rainfall is also expected to increase violent explosive eruptions.
