Humans have forced cod to shrink in size by half since 1990s, scientists find
Excessive fishing has forced Baltic cod to undergo genetic changes that have halved their size over the past 30 years, a new study has found.
The research, published in the journal Science Advances, is the first to show that decades of overfishing and environmental change can profoundly alter the genetic make-up of a fully marine species.
Baltic cod once measured more than a meter long and weighed up to 40kg, forming the backbone of the region's fishery. In the last three decades, however, the species has shrunk so much that even a full-grown cod can fit neatly on a dinner plate.
'For the first time in a fully marine species, we have provided evidence of evolutionary changes in the genomes of a fish population subjected to intense exploitation, which has pushed the population to the brink of collapse,' lead author Kwi Young Han said.
Researchers examined an archive of ear stones from 152 overexploited Eastern Baltic cod, Gadus morhua, caught in the Bornholm Basin between 1996 and 2019. The ear stones record annual growth in some fish species, similar to tree rings, making them valuable timekeepers.
They specifically looked into the growth trends of the cod over 25 years of heavy fishing and compared the changes with genetic alterations found in the species at the full genome level.
The study revealed a '48 per cent decrease in asymptotic body length' of the cod from 1996 to 2019, with indications that the species had evolved due to human interference.
Genetic variations in the cod associated with body growth showed signs of 'directional selection', researchers pointed out.
Some structural changes in the genome seemed to indicate environmental adaptation, hinting the "shrinking" had a genetic basis tied to human activity.
"Selective overexploitation has altered the genome of Eastern Baltic cod," Dr Han explained. "We see this in the significant decline in average size, which we could link to reduced growth rates.'
The study found the genomes of fast-growing cod differed systematically from slow growers, with the fast growers nearly disappearing from the Baltic.
"When the largest individuals are consistently removed from the population over many years, smaller, faster-maturing fish gain an evolutionary advantage," Thorsten Reusch, another author of the study, said. "What we're observing is evolution in action, driven by human activity. This is scientifically fascinating, but ecologically deeply concerning.'
The new research calls for conservation policies to look into the adaptive potential of marine species.
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Humans have forced cod to shrink in size by half since 1990s, scientists find
Excessive fishing has forced Baltic cod to undergo genetic changes that have halved their size over the past 30 years, a new study has found. The research, published in the journal Science Advances, is the first to show that decades of overfishing and environmental change can profoundly alter the genetic make-up of a fully marine species. Baltic cod once measured more than a meter long and weighed up to 40kg, forming the backbone of the region's fishery. In the last three decades, however, the species has shrunk so much that even a full-grown cod can fit neatly on a dinner plate. 'For the first time in a fully marine species, we have provided evidence of evolutionary changes in the genomes of a fish population subjected to intense exploitation, which has pushed the population to the brink of collapse,' lead author Kwi Young Han said. Researchers examined an archive of ear stones from 152 overexploited Eastern Baltic cod, Gadus morhua, caught in the Bornholm Basin between 1996 and 2019. The ear stones record annual growth in some fish species, similar to tree rings, making them valuable timekeepers. They specifically looked into the growth trends of the cod over 25 years of heavy fishing and compared the changes with genetic alterations found in the species at the full genome level. The study revealed a '48 per cent decrease in asymptotic body length' of the cod from 1996 to 2019, with indications that the species had evolved due to human interference. Genetic variations in the cod associated with body growth showed signs of 'directional selection', researchers pointed out. Some structural changes in the genome seemed to indicate environmental adaptation, hinting the "shrinking" had a genetic basis tied to human activity. "Selective overexploitation has altered the genome of Eastern Baltic cod," Dr Han explained. "We see this in the significant decline in average size, which we could link to reduced growth rates.' The study found the genomes of fast-growing cod differed systematically from slow growers, with the fast growers nearly disappearing from the Baltic. "When the largest individuals are consistently removed from the population over many years, smaller, faster-maturing fish gain an evolutionary advantage," Thorsten Reusch, another author of the study, said. "What we're observing is evolution in action, driven by human activity. This is scientifically fascinating, but ecologically deeply concerning.' The new research calls for conservation policies to look into the adaptive potential of marine species.
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Ancient canoe replica recreates a 30,000-year-old voyage
Instead of putting the pedal to the metal, a team of scientists from Japan and Taiwan are putting the paddle to the water–for science. The team used time-period-accurate tools to create canoes and used them to test the methods that ancient people would have used to travel across the sea in East Asia 30,000 years ago. Their results of these test paddles and findings are detailed in two new studies published June 25 in the journal Science Advances. Archaeological evidence suggests that about 30,000 years ago, humans first made a crossing from present-day Taiwan to islands in southern Japan. This journey could have ranged from 138 to about 450 miles and was accomplished without metal tools, maps, or modern boats. While the timeline of when East Asia's earliest modern human populations set sail and where they landed is fairly clear, how they did it has been more difficult to pin down. That's where these replica canoes come in. A team led by anthropologist Yousuke Kaifu from the University of Tokyo created various simulations, experiments, and replica canoes to recreate how this feat may have been achieved. 'We initiated this project with simple questions: 'How did Paleolithic people arrive at such remote islands as Okinawa?' 'How difficult was their journey?' 'And what tools and strategies did they use?'' Kaifu said in a statement. 'Archaeological evidence such as remains and artifacts can't paint a full picture as the nature of the sea is that it washes such things away. So, we turned to the idea of experimental archaeology, in a similar vein to the Kon-Tiki expedition of 1947 by Norwegian explorer Thor Heyerdahl.' One of the new studies details the construction and testing of a real boat, which the team successfully used to paddle between islands. The team constructed the 24-foot-long dugout canoe called Sugime in 2019. It was built from one Japanese cedar trunk, and with replicas of 30,000-year-old stone tools. 'A dugout canoe was our last candidate among the possible Paleolithic seagoing crafts for the region. We first hypothesized that Paleolithic people used rafts, but after a series of experiments, we learned that these rafts are too slow to cross the Kuroshio and are not durable enough,' said Kaifu. The team paddled Sugiume about 140 miles from eastern Taiwan to Yonaguni Island in southern Japan's Ryukyu group, which includes Okinawa. They navigated only by the sun, stars, swells, and their instincts. In total, the team paddled for more than 45 hours across open sea, without a lot of visibility of the island. In the six years since, the team is still unpacking some of the data they collected during the experiment, and are using it to inform or test new models about various aspects of Paleolithic sea crossings. [ Related: Southeast Asian sailors possibly mastered seafaring before Polynesians. ] 'We now know that these canoes are fast and durable enough to make the crossing, but that's only half the story,' said Kaifu. 'Those male and female pioneers must have all been experienced paddlers with effective strategies and a strong will to explore the unknown.' However, the team does not think that a return journey towards Taiwan was possible at the time. 'If you have a map and know the flow pattern of the Kuroshio, you can plan a return journey, but such things probably did not take place until much later in history,' explained Kaifu. The team also used advanced ocean models to simulate hundreds of virtual voyages, in an effort to understand if a journey like the one the modern scientists tried could have been made in different circumstances. These simulations tested several variables, including different starting points, seasons, and paddling strategies under both ancient and modern ocean conditions. Additionally, one of the new papers used numerical simulations to show how they may have crossed the Kuroshio Current–one of the strongest currents in the world. This simulation showed how boats made using tools of the time, and the right know-how, could have navigated the Kuroshio Current. 'The Kuroshio Current is generally considered dangerous to navigate,' Yu-Lin Chang, a study coauthor and oceanography student from the Japan Agency for Marine-Earth Science and Technology, said in a statement. 'I thought if you entered it, you could only drift aimlessly. But the results of our simulations went far beyond what I had imagined. I'm pleased this work helped illuminate how ocean voyages may have occurred 30,000 years ago.' These various simulations helped fill in some gaps that a simple one-time experiment could not. 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With a primitive canoe, scientists replicate prehistoric seafaring
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