1,000 tags reveal mysteries of giant bluefin tuna

Oct 29, 2008
Dr. Michael Stokesbury of Dalhousie University tags a giant bluefin caught in the Gulf of St. Lawrence off Nova Scotia, Canada. The fish, estimated at 1,250 pounds, was released with the 1,000th electronic tag deployed through the Tag-A-Giant research campaign. Credit: Tag-A-Giant

A giant Atlantic bluefin tuna weighing more than half a ton had the honor of being fitted with the 1000th electronic tracking tag placed on this threatened species when it was caught and released on Monday (October 20) in the Gulf of St. Lawrence off Port Hood, Nova Scotia.

The prized fish, which measured 10 feet in length, was tagged by a scientific team from the Tag-A-Giant (TAG; www.tagagiant.org) campaign of Stanford University, Dalhousie University and the Monterey Bay Aquarium, working in collaboration with Canadian fishermen from Prince Edward Island and Nova Scotia. The field team was led by Drs. Mike Stokesbury of Dalhousie University and Steve Wilson of Stanford University.

The TAG team has been tagging bluefin tuna since 1996, when the first tag was put out on a bluefin tuna off North Carolina's Outer Banks. Led by Stanford University professor Barbara Block, the team has traveled from the Gulf of St. Lawrence to the Gulf of Mexico and from Ireland to Spain to tag Atlantic bluefin tuna.

Placing 1,000 tags on giant bluefin has been a long quest for TAG researchers, whose work has helped to reveal the life histories of these amazing, elusive creatures at a time when their commercial value is soaring and their population has declined to a fraction of its historic levels – prompting calls for a moratorium on the commercial fishery so the Atlantic giants can recover.

The tagging data assembled by the TAG researchers have been vital in identifying how populations of bluefin tuna use the North Atlantic, leading to new discoveries about their physiology, their migratory patterns and their population structure.

Electronic tagging is a carefully orchestrated process, refined through years of experience in the field and in the Tuna Research and Conservation Center in Pacific Grove, California, which is operated jointly by Stanford University and the Monterey Bay Aquarium.

In the field, fish are caught using rod and reel and brought aboard the fishing vessel, where tags are externally attached, or surgically implanted inside the tuna. Each tag, ranging in price from US$1,500-$3,500, records sunrise and sunset, pressure (or depth), water temperature and body temperature. When months or years later a fisherman catches the tagged tuna, the fisherman receives a handsome reward for returning the electronic tag to scientists who then download the data into a computer for analysis.

Some tags do not even need to be physically retrieved but rather transmit their data to researchers via satellite. Using astronomical techniques similar to those used by 17th century mariners, the tuna's position on earth can be calculated from sunrise and sunset data, revealing the migratory track of individual fish as they swim throughout the North Atlantic Ocean and adjacent seas. The longest migration recorded to date was from a fish caught, tagged and released in North Carolina that over the course of 4.8 years traveled across the North Atlantic and into the Mediterranean.

Bluefin tuna are often described with superlatives: largest, fastest, most powerful. They are long-lived, among the largest fish on earth—weighing up to 1,500 lbs—and make trans-oceanic migrations in as few as 20 days.

The same muscles that power their locomotion across ocean basins are at the heart of the sushi economy that has made the bluefin so prized by diners. Global demand for bluefins has grown dramatically in recent years, and sushi connoisseurs revere bluefin tuna above all else. A single fish sold at auction in Japan for $173,000 – pricing that has fueled industrial fishing pressure and has led to the near-collapse of bluefin populations in both the West and East Atlantic.

Tag-A-Giant research is providing fisheries managers with the information needed to design and implement sustainable limits for commercial and recreational fisheries for bluefin tuna to reverse the decline and put the species on the road to recovery.

Data from the tagged fish have revealed that bluefin tuna routinely swim across the Atlantic, with fish tagged off the coast of North America visiting spawning grounds in the Mediterranean and in the Gulf of Mexico. The data show that the western and eastern populations forage together on common fishing grounds, then move to distinct spawning grounds when it is time to breed. As a result, fish from both populations are affected by fisheries on both sides of the Atlantic.

The tagging data were recently confirmed using a completely different technique, based on chemical analysis of the tunas' "otoliths," or ear bones, which retain a characteristic chemical signature depending upon where the tuna was originally spawned.

A unique aspect of this study, published in the journal Science, shows that the large fish that visit the northern waters of Canada are derived primarily from the Gulf of Mexico breeding stock, and that and that there is a mixture of fish from both Gulf of Mexico and Mediterranean stocks in waters along the U.S. continental shelf.

The electronic tags have also revealed these giant tuna dive to depths of nearly a mile and range through waters from the tropics to frigid polar seas. They can do so because bluefins are among the rare ocean animals that have the capacity to maintain a warm, stable body temperature throughout their wide thermal niche – much like a mammal or bird.

TAG data have also helped to uncover where, when and how bluefin tuna spawn, at what age they mature, and are helping to increase the accuracy of population estimates for Atlantic bluefin tuna.

The 1,000th tag is riding on the back of a bluefin tuna, recording its every move. Of the 1,000 tags deployed since 1996, approximately half have been recovered or reported back, documenting more than 21,000 days of tuna behavior. The remaining tags are still at large on giants swimming in the North Atlantic, Mediterranean and Gulf of Mexico.

The TAG team continues to pursue its work, collecting new information that will help ensure a future for Atlantic bluefin tuna.

Source: Tag-A-Giant Foundation (The Ocean Foundation)

Explore further: Diabetes drug found in freshwater is a potential cause of intersex fish

Related Stories

Biodiversity promotes multitasking in ecosystems

36 minutes ago

A new study of the complex interplay between organisms and their environment shows that biodiversity—the variety of organisms living on Earth—is even more important to the healthy functioning of ecosystems ...

Japan has floating solar power plants in Hyogo Prefecture

38 minutes ago

Kyocera is in the news this month. Two floating solar power plants in two reservoirs in Kato City, Hyogo Prefecture, Japan, are complete. This is a joint venture. The two players are Kyocera and Century Tokyo ...

Apple wins patent appeal in China

1 hour ago

Apple has won an appeal in China over patent rights to voice recognition software such as the iPhone's "Siri", with a court overruling an earlier decision that had gone against the US technology giant.

Recommended for you

Two new iguanid lizard species from the Laja Lagoon, Chile

23 minutes ago

A team of Chilean scientists discover two new species of iguanid lizards from the Laja Lagoon, Chile. The two new species are believed to have been long confused with other representatives of the elongatus-kriegi ...

New 3-D method improves the study of proteins

1 hour ago

Researchers have developed a new computational method called AGGRESCAN3D which will allow studying the 3D structure of folded globular proteins and substantially improve the prediction of any propensity for ...

ANZAC grevillea hybrid marks centenary celebrations

1 hour ago

Through an intense breeding program of native flora, Kings Park botanists have provided the Western Australian RSL with a commemorative grevillea (Proteaceae) in time for the Anzac Centenary.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.