Quantcast
Environmental News for a Healthier Planet and Life

Help Support EcoWatch

Blue Sharks Are True Globalists, Tagging Data Shows

Animals
Blue Sharks Are True Globalists, Tagging Data Shows
A blue shark in the Channel Islands off California. NOAA SWFSC/Flickr

By Jasmin Graham

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.

But blue sharks are often caught unintentionally as bycatch along with targeted fish. They are classified as near threatened, and there is evidence that their population is decreasing.

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.

Blue sharks range throughout the world's tropical and temperate oceans (blue zones). IUCN Redlist/Wikipedia / CC BY-SA

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.

An electric car at an eVgo charging station in a parking lot in Dublin, California on June 20, 2018. Smith Collection / Gado / Getty Images

California Governor Gavin Newsom signed an executive order Wednesday that would ban the sale of new cars in California that run only on gasoline by the year 2035. The bid to reduce emissions and combat the climate crisis would make California the first state to ban the sale of new cars with internal combustion engines, according to POLITICO.

Read More Show Less

EcoWatch Daily Newsletter

A "trash tsunami" has washed ashore on the beaches of Honduras, endangering both wildlife and the local economy.

Read More Show Less

Trending

Long-finned pilot whales are seen during a 1998 stranding in Marion Bay in Tasmania, Australia. Auscape / Universal Images Group / Getty Images

More long-finned pilot whales were found stranded today on beaches in Tasmania, Australia. About 500 whales have become stranded, including at least 380 that have died, the AP reported. It is the largest mass stranding in Australia's recorded history.

Read More Show Less
A protest in solidarity with the Wetʼsuwetʼen's anti-pipeline struggle, at Canada House in Trafalgar Square on March 1, 2020 in London, England. More than 200 environmental groups had their Facebook accounts suspended days before an online solidarity protest. Ollie Millington / Getty Images

Facebook suspended more than 200 accounts belonging to environmental and Indigenous groups Saturday, casting doubt on the company's stated commitments to addressing the climate crisis.

Read More Show Less
The Västra Hamnen neighborhood in Malmö, Sweden, runs on renewable energy. Tomas Ottosson / Wikimedia Commons / CC by 3.0

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.

Read More Show Less

Support Ecowatch