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CONTACT: Stanford University News Service (650) 723-2558 COMMENT: Barbara Block, Hopkins Marine Station (408) 655-6236
At Monterey Bay Aquarium: Ken Peterson (408) 648-4922

Aquarium, Stanford researchers team up to place tunas on view

STANFORD --At a preview for the Monterey Bay Aquarium's new Outer Bay Galleries on Jan. 27, a glistening school of yellowfin tunas created a sensation in the centerpiece million-gallon tank. Standing before an enormous two-story window, visitors young and old marveled at 80 streamlined tunas swimming before their eyes through the seemingly boundless waters of the Outer Bay exhibit. Viewers saw yellowfin bursting to the water's surface for a morsel of food before gliding down to join the school in deeper waters.

Stanford biologist Barbara Block seemed as delighted as any first-time visitor. An expert on tunas and other open ocean fish, she has seen them feeding thousands of times, but seldom from such a vantage point, as if watching from under the sea.

"You cannot help but be fascinated when you see that window and see the beauty of these fish," said Block. "These are majestic creatures that in every ocean are under fire."

The Monterey Bay Aquarium officially opens its new galleries on March 2. They feature tunas and anchovies, jellyfish and ocean sunfish - all creatures of the open ocean at the outer fringes of Monterey Bay. Exhibiting the tunas was a special challenge - these are ocean nomads, ranging over as much as 12,000 miles of open sea each year. To learn how to keep them healthy in a much smaller space took the expertise of the aquarium's skilled animal husbandry team, plus a unique collaboration with its next-door neighbor on the bay

That neighbor is Hopkins Marine Station, Stanford University's marine biology research facility and the West Coast's oldest marine laboratory. In 1994, Hopkins and the aquarium joined forces to build the Tuna Research and Conservation Center. Its co-directors are Block, an assistant professor of biology at Stanford, and Chuck Farwell, curator of pelagic fish at Monterey Bay Aquarium.

Farwell and his team of aquarists have developed techniques over the past six years to safely capture, transport and care for captive tunas. Block added expertise gained over years of following the fish in the open ocean to study their habits and physiology. The eighty tunas now in the million-gallon exhibition tank at the aquarium, plus 90 research fish held in three 90-gallon tanks at the research center, represent the largest tunas - in both size and number - ever studied in captivity.

According to Block, the research center and the aquarium have intertwining goals: to learn more about the basic biology of tunas, one of the world's few warm-blooded fish; and to educate the public and raise concern about tuna conservation. Worldwide, tunas represent the most valuable marine fishery. Some species - like Atlantic bluefin tunas - are potentially endangered.

Julie Packard, executive director of the aquarium, said research on tunas at the center also furthers conservation efforts by providing information to help manage ocean resources.

"There's a vast storage of biological information that we are only beginning to explore, especially in the oceans," Packard said.

"Too often we make [resource management] decisions based on inadequate information."

In its first year of operation, the research center's main purpose has been to teach both aquarists and scientists about the environment that tunas need to survive, Block said. "What we are doing is basically writing the book on what it takes to be a healthy tuna."

Playing tuna tag

"Aren't they beautiful?" Block asks as she leans over a circular fish tank at the tuna research center and runs her hand across the water's surface to draw the attention of yellowfin tunas swimming past. Below her hand stream the gleaming backs and yellow-tipped fins of some of the 90 research tunas kept at the center.

Block and her graduate students and postdoctoral fellows work with the tunas in three tanks to study their eating habits, temperature preferences and the best ways to attach tags to the fish to obtain information about their inner workings and environmental preferences.

Experiments on tunas' food intake already have uncovered ways to improve the health of exhibit tunas, Block said. "It turns out that we were raising what appeared to be 'couch potatoes' and feeding them what might be called 'doritos' - a lot of fat."

Autopsies on research center tunas that had died revealed high deposits of fat in their bodies, so tunas exhibited in the large tank at the aquarium were switched to a leaner diet, she said.

Another experiment compares two tanks of tunas kept at different temperatures to determine the best water conditions for healthy tunas.

In 1994, Block and fellow researchers tagged yellowfin tunas off the coast of Southern California and monitored their preferred temperature range and water depth. They found that the tunas preferred to stay in the warmest water available, 68 to 72 degrees Fahrenheit. Now, graduate student David Marcinek is conducting a six-month study at the research center comparing the health of fish maintained in this temperature range and a warmer one.

New methods for tagging fish

Block also is using the fish at the center to research better methods of attaching torpedo-shaped tags to their backs.

For years, researchers have studied tunas and other large ocean fish by capturing the animals, tagging them with acoustic probes and following the released fish as they travel the open oceans.

Block is developing a muscle tag that uses sound waves to monitor heart rate and other physiological parameters. She is working in collaboration with biologist Heidi Dewar of the Monterey Bay Aquarium Research Institute and engineer Max Deffenbaugh of the Massachusetts Institute of Technology.

Block hopes to use the muscle-probing tags to learn about the benefit to tunas of their warm-blooded lifestyle. The power output of their muscles will be compared to that of their cold-blooded cousins, the bonitos, swimming in tanks at the center alongside the yellowfin.

"We're now geared up for an entire suite of experiments," Block said. "We can actually listen to the muscles of warm-blooded animals and cold-blooded animals."

Work also is continuing on tags that contain computer-based microprocessors that can store large amounts of information such as water temperature, ocean depth and the position of the fish in the water.

The most revolutionary variation of this tag can beam data up to a satellite. Until now, researchers have had to retrieve animals from the sea to get data tags back. The satellite tag, which may one day log up to seven years of data, will allow researchers to wait for the data to come to them. The tag will pop off a tuna out in the open ocean, bob up to the surface and send to the satellite the tuna "travel-log" of information.

The satellite tags will provide researchers with an understanding of tunas' migratory patterns. This information can be combined with genetic studies that reveal whether tunas in different oceans exist as separate populations. In combination, the results will clarify whether overfishing of tunas in one part of the ocean is masked by tuna migration from other regions.

Block also is using DNA fingerprinting to determine whether distinct genetic pockets of blue marlin and swordfish exist in different oceans throughout the world, or if they have more global populations.

Even the animals on exhibit in the aquarium have answered questions about wild tunas.

Researchers had noticed at sea that schools of tuna move up and down in the water like yo-yos. The fish were thought to do this to save energy, gliding down in the water, then thrusting with their tail fins to get back up closer to the surface. Watching from a ship on the water's surface, researchers had no way to confirm this idea.

That swimming pattern was the first thing Block noticed as she watched them through the giant window of the aquarium tank. "It was just like we thought," she said. "They glide down, then thrust back up."

Each piece of new knowledge will contribute to Block's and Farwell's "book" on what it takes to make a healthy tuna, bolstering the goals of the collaboration between the center and the aquarium: to preserve the tunas' counterparts in the wild and to ensure the future place of nomadic tunas on the ocean landscape.

And for Block and other scientists who study open-ocean fish, the tuna research center represents a unique opportunity: the first time that a large school of large fish have been available to study in captivity.

"The level of sophistication of the science goes way down [at sea]," she said. "Having a captive population to test your engineering ideas on is about as good as it gets in science."

Barbra Rodriguez is a science writing intern at the Stanford News Service.



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