Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Satellite technology allows scientists to track warm sharks in cold polar seas

07.10.2005


Electronic tags broadcasting from the dorsal fins of salmon sharks reveal that these top predators migrate from the glacial waters of Alaska to the warm seas off Hawaii, according to a new study in the journal Science. The salmon shark’s ability to survive such a broad range of thermal conditions is attributed to high levels of specialized proteins that keep its heart muscle cells beating at very low temperatures, say the study’s authors.



"Sharks are declining globally, yet the movements and habitats of most species are unknown," says Stanford University biologist Barbara Block, chief scientist of the study, which included researchers from the National Marine Fisheries Service (NMFS), Monterey Bay Aquarium and the Alaska Department of Fish and Game. The research was conducted as part of the Census of Marine Life, an international network of scientists seeking to understand the abundance and diversity of life in the oceans.

Dual tagging technology


Writing in the Oct. 7 issue of Science, Block, Stanford doctoral student Kevin Weng and their colleagues compared the migration and unique cardiac physiology of the salmon shark--a close relative of the white shark--with the warmer, subtropical migration and physiology of the blue shark, another large predator.

In the study, the scientists used two kinds of satellite tagging technology. One, known as the Smart Position-Only Tag (SPOT), tracks individual sharks in real time as they migrate across the sea. The SPOT tag is attached to the tip of the dorsal fin, and when the shark surfaces, the exposed tag transmits the animal’s position to orbiting satellites. Scientists can then download the data and follow the shark’s day-to-day movements on their computers back home. In fact, this technology allows anyone with Internet access to track the sharks’ daily migration in near-real time on a web browser: http://www.toppcensus.org.

"I like to check on the position of the sharks with my coffee every morning," says Block, the Charles and Elizabeth Prothro Professor in Marine Sciences at Stanford’s Hopkins Marine Station.

The second technology, called the Pop-Up Satellite Archival Tag (PAT), records water pressure, temperature and light while the animal swims. Unlike SPOTs, which remain fastened to the fin, PATs detach from the animal on a pre-programmed date, then float to the surface and begin transmitting data to orbiting satellites. Combining the two technologies allowed Block and her colleagues to generate a rich dataset that included highly accurate details about each shark’s position and diving behavior, as well as surrounding oceanographic conditions.

"We combined radio uplinking SPOTs that give us accurate positions and data-logging PATs that store information for the duration of the programmed mission," Block explains. "By using two types of tags, we’re able to accumulate a larger dataset on the sharks’ habitat and preferences with a greater accuracy than we’ve been able to do before."

Seasonal migrations

To tag salmon sharks, Block and her colleagues traveled to Prince William Sound in the Gulf of Alaska during the summer. There, in calm fjords, they encountered acrobatic sharks leaping after pink, coho and other varieties of salmon returning to spawn. From 2002 to 2004, the scientists tagged 51 female salmon sharks. For comparison, co-author David Holts, a biologist with NMFS, led the researchers to the Southern California coast, where 31 blue sharks were outfitted with SPOT and PAT tags.

During the three-year study, the scientists obtained tracking data from 48 of the 51 salmon sharks. Twenty-one were double-tagged with SPOT and PAT instruments, while 27 carried one tag or the other. Six sharks were recaptured during the study, including three outfitted with pop-up tags containing full archival records of the sharks’ minute-by-minute behavior. The longest distance traveled by an individual shark was 11,321 miles over 640 days--equivalent to traveling nearly halfway around the Earth.

All told, researchers collected more than 13,000 days of positional tracking data from the salmon sharks. "These data reveal a striking seasonal migration from subarctic to temperate and subtropical regions, presumably to forage or give birth to their young," says Weng, lead author of the study. In contrast, the satellite data showed that blue sharks remain in warmer Pacific waters off the continental United States and Mexico.

"The ability to follow many individuals for a year, and in some cases for two or more years, is virtually unprecedented," Weng notes.

To date, the researchers have used combined tagging on two other shark species, makos and common threshers. Block predicts that widespread use of this technique will provide much needed information about how sharks use the oceans. "From these data we can map areas of high use, visualize shark migration corridors and identify species-specific hot spots where shark populations may benefit from increased protection," she adds.

Warm bodies, cold hearts

The researchers also discovered that while some salmon sharks remain in the North Pacific for the entire year, others travel thousands of miles south to the subtropical waters of the Hawaiian Islands. During these long migrations, they encounter water temperatures ranging from 36 to 75 F (2 to 24 C). While in the cold subarctic, the sharks ranged between near-surface waters and depths as great as 450 feet.

"Sometimes in winter the surface waters, which are less salty, were so cold that the sharks spent more time in warmer, saltier waters below," Block notes. "When I glimpsed the sharks’ radio positions from these frigid seas, I often wondered what it would be like to overwinter in the wilds of an Alaska fjord chasing herring in constant darkness."

As they move farther south, the sharks spend more time in deeper water, sometimes diving about a half-mile below sea level to avoid warmer temperatures at the surface.

The capacity to summer in the plankton-rich seas of the temperate north or to overwinter in chilly Alaskan waters sets salmon sharks apart from other laminids, a family that includes mako, white and porbeagle sharks. All laminids share the unusual ability of maintaining an internal body temperature that’s up to 70 F warmer than the surrounding water. But the capacity to elevate internal body temperature does not extend to the heart, which is constantly flooded with blood that cools to ambient water temperatures as it passes through the gills to pick up oxygen.

As part of the Science study, the researchers sought to understand why the salmon shark’s heart continues to function when it is ice cold. "The shark heart slows down in the cold, just as our own heart would," Block says. "But what sets it apart is where our heart would simply stop, the salmon shark keeps on ticking."

Laboratory analysis of heart tissue from six salmon sharks revealed high levels of specialized proteins that control the release and uptake of calcium ions, which are responsible for maintaining rhythmic cardiac contractions. The researchers discovered that the rate of calcium uptake by these proteins was about 10 times faster in salmon shark hearts than in blue sharks, which inhabit much warmer water. This finding may explain the ability of salmon sharks to maintain their heart beat and supply their warm, active bodies with blood even as the heart cools to 35 F.

"This is clearly a unique shark species--the warmest of all gill-breathers in the ocean," Block observes.

The salmon shark project is part of the Tagging of Pacific Pelagics (TOPP) initiative, a research program affiliated with the Census of Marine Life. TOPP scientists use electronic tags to study the migrations of 22 species of marine animals throughout the North Pacific.

"Many sharks are threatened by fishing around the world, and biological knowledge is urgently needed to design management strategies," the authors wrote. "Satellite tracking technologies can be used to rapidly map shark habitats worldwide, which is critical to their future protection."

Mark Shwartz | EurekAlert!
Further information:
http://www.stanford.edu
http://www.toppcensus.org

More articles from Studies and Analyses:

nachricht The Great Unknown: Risk-Taking Behavior in Adolescents
19.01.2017 | Max-Planck-Institut für Bildungsforschung

nachricht A sudden drop in outdoor temperature increases the risk of respiratory infections
11.01.2017 | University of Gothenburg

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Quantum optical sensor for the first time tested in space – with a laser system from Berlin

For the first time ever, a cloud of ultra-cold atoms has been successfully created in space on board of a sounding rocket. The MAIUS mission demonstrates that quantum optical sensors can be operated even in harsh environments like space – a prerequi-site for finding answers to the most challenging questions of fundamental physics and an important innovation driver for everyday applications.

According to Albert Einstein's Equivalence Principle, all bodies are accelerated at the same rate by the Earth's gravity, regardless of their properties. This...

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Tracking movement of immune cells identifies key first steps in inflammatory arthritis

23.01.2017 | Health and Medicine

Electrocatalysis can advance green transition

23.01.2017 | Physics and Astronomy

New technology for mass-production of complex molded composite components

23.01.2017 | Process Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>