Blue Sharks Are True Globalists, Tagging Data Shows
Blue sharks are among the widest-ranging shark species in the oceans. We know this partly because from 1962 to 2013, 117,962 blue sharks were tagged as part of the ongoing Cooperative Shark Tagging Program.
This partnership between the commercial fishing industry, the U.S. government, recreational fishermen and academic research scientists is the longest-running tagging program in the world. Since its launch in 1962, participants have tagged hundreds of thousands of sharks representing 35 different species.
A dart tag, one type used in the Cooperative Shark Tagging Program. NOAA
More than half (51%) of the animals tagged were blue sharks (Prionace glauca) – a total of 117,962 individual sharks. This is probably because blues are abundant: They are found in all of the world's oceans, as far north as Alaska and as far south as Chile, but rarely venture near shore.
Unlike some other sharks, blues are not a prized commercial species, likely because most people think they taste disgusting. That makes fishermen willing to tag and release them instead of harvesting them.
Each tag attached to a shark carries an identification number and contact information, so that recaptures can be reported and matched to data collected during the initial tagging. The data show that these sharks really move. One traveled a record-breaking 3,997 nautical miles from waters off Long Island, New York, where it was first tagged, to the south Atlantic where it was recaptured – a distance longer than the Great Wall of China.
The sharks were caught in all seasons throughout their range, in tropical waters warmer than 68 degrees Fahrenheit (20 degrees Celsius) and temperate waters, which range from 50°-68°F (10°-20°C). In more tropical climates, blue sharks occupy waters as deep as 1,150 feet (350 meters), which are cooler than water near the surface. Their ability to inhabit a wide range of depths enables them to move around as seasons and water temperatures change.
Tagging data confirm that blue sharks migrate incredibly long distances, with some even crossing the equator from the North Atlantic to the South Atlantic. All of this movement allows them to mix and mingle with individuals throughout their range. This tells scientists that all blue sharks in the Atlantic Ocean are part of one mating pool, and can be considered one big population, rather than smaller separate groups.
The fact that blue sharks range so widely suggests that an event in one part of the Atlantic, such as an oil spill, could potentially affect the number of mating pairs across the population. This could reduce the number of blue sharks in the next generation and lead to a decline in their population throughout the Atlantic. It could also reduce their genetic diversity and make the survivors more prone to mortality from disease.
About 7% of the tagged blue sharks (8,213) were recaptured later, sometimes after more than a decade. One shark was recaptured nearly 16 years after it was first tagged. Scientists estimated that this shark was between 8 and 11 years old at the time it was tagged, based on its size. That original age estimate would have made the shark 24 to 27 years old when it was recaptured, which falls within the current estimated range of maximum age for the species.
Thanks to tagging data, scientists have learned a lot about the ecology of several species, including smooth dogfish and sandbar sharks. As a scientist pursuing a career in marine conservation, I look forward to more wondrous discoveries about these marvelous animals.
Reposted with permission from The Conversation.
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- Redwoods are the world's tallest trees.
- Now scientists have discovered they are even bigger than we thought.
- Using laser technology they map the 80-meter giants.
- Trees are a key plank in the fight against climate change.
They are among the largest trees in the world, descendants of forests where dinosaurs roamed.
Pixabay / Simi Luft<p><span>Until recently, measuring these trees meant scaling their 80 meter high trunks with a tape measure. Now, a team of scientists from University College London and the University of Maryland uses advanced laser scanning, to create 3D maps and calculate the total mass.</span></p><p>The results are striking: suggesting the trees <a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank" rel="noopener noreferrer">may be as much as 30% larger than earlier measurements suggested.</a> Part of that could be due to the additional trunks the Redwoods can grow as they age, <a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank" rel="noopener noreferrer">a process known as reiteration</a>.</p>
New 3D measurements of large redwood trees for biomass and structure. Nature / UCL<p>Measuring the trees more accurately is important because carbon capture will probably play a key role in the battle against climate change. Forest <a href="https://www.wri.org/blog/2020/09/carbon-sequestration-natural-forest-regrowth" target="_blank">growth could absorb billions of tons</a> of carbon dioxide from the atmosphere each year.</p><p>"The importance of big trees is widely-recognised in terms of carbon storage, demographics and impact on their surrounding ecosystems," the authors wrote<a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank"> in the journal Nature</a>. "Unfortunately the importance of big trees is in direct proportion to the difficulty of measuring them."</p><p>Redwoods are so long lived because of their ability to <a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank" rel="noopener noreferrer">cope with climate change, resist disease and even survive fire damage</a>, the scientists say. Almost a fifth of their volume may be bark, which helps protect them.</p>
Carbon Capture Champions<p><span>Earlier research by scientists at Humboldt University and the University of Washington found that </span><a href="https://www.sciencedirect.com/science/article/pii/S0378112716302584" target="_blank" rel="noopener noreferrer">Redwood forests store almost 2,600 tonnes of carbon per hectare</a><span>, their bark alone containing more carbon than any other neighboring species.</span></p><p>While the importance of trees in fighting climate change is widely accepted, not all species enjoy the same protection as California's coastal Redwoods. In 2019 the world lost the equivalent of <a href="https://www.worldwildlife.org/threats/deforestation-and-forest-degradation" target="_blank" rel="noopener noreferrer">30 soccer fields of forest cover every minute</a>, due to agricultural expansion, logging and fires, according to The Worldwide Fund for Nature (WWF).</p>
Pixabay<p>Although <a href="https://c402277.ssl.cf1.rackcdn.com/publications/1420/files/original/Deforestation_fronts_-_drivers_and_responses_in_a_changing_world_-_full_report_%281%29.pdf?1610810475" target="_blank" rel="noopener noreferrer">the rate of loss is reported to have slowed in recent years</a>, reforesting the world to help stem climate change is a massive task.</p><p><span>That's why the World Economic Forum launched the Trillion Trees Challenge (</span><a href="https://www.1t.org/" target="_blank" rel="noopener noreferrer">1t.org</a><span>) and is engaging organizations and individuals across the globe through its </span><a href="https://uplink.weforum.org/uplink/s/uplink-issue/a002o00000vOf09AAC/trillion-trees" target="_blank" rel="noopener noreferrer">Uplink innovation crowdsourcing platform</a><span> to support the project.</span></p><p>That's backed up by research led by ETH Zurich/Crowther Lab showing there's potential to restore tree coverage across 2.2 billion acres of degraded land.</p><p>"Forests are critical to the health of the planet," according to <a href="https://www.1t.org/" target="_blank" rel="noopener noreferrer">1t.org</a>. "They sequester carbon, regulate global temperatures and freshwater flows, recharge groundwater, anchor fertile soil and act as flood barriers."</p><p><em data-redactor-tag="em" data-verified="redactor">Reposted with permission from the </em><span><em data-redactor-tag="em" data-verified="redactor"><a href="https://www.weforum.org/agenda/2021/03/redwoods-store-more-co2-and-are-more-enormous-than-we-thought/" target="_blank">World Economic Forum</a>.</em></span></p>
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