Keeping tags on tuna:
Pop-up satellite technology successfully tracks migration
BY DAVID F. SALISBURY
A new satellite-based
tagging technology has proven that it can help resolve
the mysteries of tuna migration at a time when management
strategies for these remarkable and commercially valuable
fish are in dispute and their breeding population is in
sharp decline.
The microprocessor tags,
deployed in 1996 and 1997 by scientists from Stanford
University, the Monterey Bay Aquarium and the National
Marine Fisheries Service, revealed that tunas tagged off
Cape Hatteras, N.C., were able to move as far as 1,670
nautical miles in 90 days and that some fish crossed
the internationally established line separating eastern
and western management zones for the bluefin fishery.
"The results of our
work indicate that pop-up technology works, and that
survivorship is high. The fact that the bluefin spread
out in 90 days across the western Atlantic and into the
western margins of the eastern Atlantic management zone
indicates these fish are on the move," said Dr.
Barbara Block of the Tuna Research and Conservation
Center (TRCC), a collaborative effort between Stanford
University and the Monterey Bay Aquarium.
The findings appear in the
Aug. 4 issue of the Proceedings of the National
Academy of Sciences.
Researchers
release a giant Atlantic bluefin tuna into the ocean,
bearing a computerized “tag” to track its
travels and physiology.
Stanford
University and Monterey Bay Aquarium
The new tags,
called satellite pop-up tags, pop free of the fish at a
preprogrammed time, float to the surface and beam their
accumulated data via satellite to scientists in the lab
to reveal where the fish moved and what ocean
temperatures they favored.
Giant bluefin tuna, which
can fetch as much as $80,000 apiece in the Tokyo seafood
market, currently are managed as two separate Atlantic
stocks with limited mixing between the western and
eastern Atlantic. Coincident with this management
strategy, breeding stocks in the western Atlantic have
declined by more than 80 percent over the past 22 years,
and eastern Atlantic bluefin of similar ages have fallen
by 50 percent during the same period. Western Atlantic
tuna are managed under a strict annual quota; eastern
Atlantic bluefin have been managed under catch quotas
only since 1995, with a 25 percent reduction to be fully
implemented this year.
"It's now possible
and imperative to make use of satellite tag technology
to determine the extent of transatlantic
migrations," Block says. "In that way,
management strategies can reflect fish behavior in the
real world. With this technology it will be possible to
manage giant bluefin tuna so mature breeding stocks could
recover in our lifetime."
A 1994 report by the
National Research Council recommended that fisheries
scientists test the stock structure theories to confirm
whether bluefin tuna are one or two stocks in the
Atlantic Ocean.
"We believe that the
advanced tagging technologies currently being applied to
Atlantic bluefin tuna could provide essential information
for resolving questions about the existence of one or two
management units," said Eric Prince, chief of the
migratory fishery biology division of the National Marine
Fisheries Service in Miami.
According to Block, the
satellite tags can be used to provide similar information
about other pelagic fish species whose lives are equally
mysterious. To date, she and her colleagues have put the
tags on bluefin and yellowfin tuna, blue and striped
marlins and salmon sharks.
What sets the satellite
tags apart from other fish-tagging methods is the fact
that scientists can recover the data without relying on
tagged fish being caught and the tags voluntarily turned
in to their labs by fishermen.
Historically, about 13
percent of conventional bluefin tags have been recovered.
In the 1996 and 1997 experiments, data were recovered
from 35 of 37 satellite tags. Importantly, this indicates
high survivorship of the tag-and-release fish.
The tags were developed in
collaboration with Paul Howey of Telemetry 2000 Inc.
Tagging took place in a collaboration among the TRCC, the
National Marine Fisheries Service (NMFS) and the
recreational fishing community off Cape Hatteras. The
research was financed by the National Marine Fisheries
Service, the Packard Foundation, the MacArthur Foundation
and the National Science Foundation.
Wild fish up to 234 kg
were tagged at Cape Hatteras with techniques developed
using captive yellowfin tuna at the TRCC. Extensive work
with captive tunas demonstrated that the tags can be
attached without harm to the fish, either in the lab or
in the field.
Data from the 1997 study
found that two out of the 37 bluefin tuna crossed between
management zones and four additional bluefin were within
5 degrees longitude of the stock boundary meridian.
Researchers with the TRCC
and NMFS plan to tag between 600 and 1,000 giant Atlantic
bluefin tuna by the year 2000. This will enable them to
rigorously test the stock structure hypothesis.
[For copies of the paper,
please contact the Office of News and Public Information
at the Proceedings of the National Academy of Sciences,
(202) 334-2138; pnasnews@nas.edu.] SR
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