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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By Harry Kretchmer
By 2030, almost a third of all the energy consumed in the European Union must come from renewable sources, according to binding targets agreed in 2018. Sweden is helping lead the way.
Sweden is a world leader in renewable energy consumption. Swedish Institute/World Bank
Naturally Warm<p>54% of Sweden's power comes from renewables, and is helped by its geography. With plenty of moving water and 63% forest cover, it's no surprise the <a href="https://sweden.se/nature/energy-use-in-sweden/#" target="_blank">two largest renewable power sources</a> are hydropower and biomass. And that biomass is helping support a local energy boom.</p><p>Heating is a key use of energy in a cold country like Sweden. In recent decades, as fuel oil taxes have increased, the country's power companies have turned to renewables, like biomass, to fuel local 'district heating' plants.</p><p>In Sweden these trace their <a href="https://www.sciencedirect.com/science/article/pii/S0360544217304140#fig3" target="_blank">origins back to 1948</a>, when a power station's excess heat was first used to heat nearby buildings: steam is <a href="https://www.sciencedirect.com/topics/engineering/district-heating-system" target="_blank">forced along a network of pipes</a> to wherever it's needed. Today, there are around 500 district heating systems across the country, from major cities to small villages, providing heat to homes and businesses.</p><p>District heating used to be fueled mainly from the <a href="https://www.sciencedirect.com/science/article/pii/S0360544217304140" target="_blank">by-products of power plants</a>, waste-to-energy plants and industrial processes. These days, however, Sweden is bringing more renewable sources into the mix. And as a result of competition, this localized form of power is now the country's<a href="https://www.sciencedirect.com/science/article/pii/S0360544217304140#fig3" target="_blank" rel="noopener noreferrer"> home-heating market leader.</a></p>
Sweden is using smart grids to turn buildings into energy producers. Huang et al/Elsevier
Energy ‘Prosumers’<p>But Sweden doesn't stop at village-level heating solutions. Its new breed of energy-generation takes hyper-local to the next level.</p><p>One example is in the city of Ludivika where 1970s flats <a href="https://www.buildup.eu/sites/default/files/content/transforming-a-residential-building-cluster-into-electricity-prosumers-in-sweden.pdf" target="_blank">have recently been retrofitted with the latest smart energy technology</a>.</p><p>48 family apartments spread across 3 buildings have been given photovoltaic solar panels, thermal energy storage and heat pump systems. A micro energy grid connects it all, and helps charge electric cars overnight.</p><p>The result is a cluster of 'prosumer' buildings, producing rather than consuming enough power for 77% of residents' needs. With <a href="http://www.diva-portal.org/smash/get/diva2:1232060/FULLTEXT01.pdf" target="_blank" rel="noopener noreferrer">high levels of smart meter usage</a>, it's a model that looks set to spread across Sweden.</p>
<div id="d7bf9" class="rm-shortcode" data-rm-shortcode-id="8757b138d5570bec9d6aad18074a429a"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1273556364263071744" data-partner="rebelmouse"><div style="margin:1em 0">Read more about Western Harbour and book a visit: https://t.co/ujSmVs9rNK 🏡🌳🌊 https://t.co/C5PuPziqIM</div> — Smart City Sweden (@Smart City Sweden)<a href="https://twitter.com/SmartCitySweden/statuses/1273556364263071744">1592474473.0</a></blockquote></div>
Scaling Up<p>A recent development by E.ON in Hyllie, a district on the outskirts of Malmö, southern Sweden, <a href="https://www.eonenergy.com/blog/2019/February/sweden-smart-city" target="_blank">has scaled up the smart grid principle</a>. Energy generation comes from local wind, solar, biomass and waste sources.</p><p>Smart grids then balance the power, react to the weather, deploying extra power when it's colder or putting excess into battery storage when it's warm. The system is not only more efficient, but bills have fallen.</p><p>Smart energy developments like those in Hyllie, Ludivika, and renewable-driven district heating, offer a radical alternative to the centralized energy systems many countries rely on today.</p><p>The EU's leaders have a challenge: how to generate 32% of energy from renewables by 2030. Sweden offers a vision of how technology and local solutions can turn a goal into a reality.</p>
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