I recently found an old story I wrote while looking up some information about tagging and its benefits. When “Migratory Movements, Depth Preferences, and Thermal Biology of Atlantic Bluefin Tuna” was published in the 17 August 2001 issue of Science there were some great stories to tell. Stories that had to be kept as secrets until the paper was published in Science.
The data presented, and conclusions drawn from them by a team headed by Dr. Barbara Block from Stanford University (and including scientists, anglers and crew making up a who’s who of tuna angling , research and management) created shocks waves across the Atlantic.
National Public Radio, National Geographic News as well local, regional and national newspapers, had already discussed the ramifications of having tuna tagged off Hatteras, cross the Atlantic Ocean, and even enter the Mediterranean Sea in larger numbers than any previous estimates could imagine. This threw a monkey wrench into all management plans and conservation attempts, based on earlier theories, that eastern and western populations of bluefin tuna were separate and need to be managed separately.
Two types of tags were used in the study, surgically applied internal “archival” tags and pop-up satellite archival tags (PSAT tags in the article’s jargon). Both showed that fish from the west cross over into the eastern Atlantic. These tags, plus captured fish with conventional spaghetti tags, raised the thorny issue of North American fishermen (commercial and recreational) accepting low catch quotas in order to allow the overfished tuna populations to recover, only to have the fish massacred in huge numbers in the Mediterranean and eastern Atlantic. (East of longitude 45 degrees West twenty metric tonnes of bluefin tuna were being caught for every tonne caught in the west!)
The Science paper is fascinating but takes some serious reading! It is not something you can glance at and retain. Some highlights, with some input from me from information gleaned during the tagging process, include:
There were 377 electronic tags in this study. Electronic tags were recovered from a few days to 3.6 years later, AND the TAG program continues to produce amazing results. Internal archival tags totaled 279 with 49 tuna being recaptured. This 18% return rate is extremely high and by itself suggests overfishing.
The 90% data acquisition rate from pop-up tags is a marvel of both technology and tuna survival rates. The return rate is higher since the fish does not have to be recaptured and the data is downloaded through the Argos satellite system. Although, the percentage of recovery is higher less information per tag can be retrieved, because of the high energy needed to send a radio signal, not just burn data onto a chip.
There were 7065 conventional spaghetti tags applied by Carolina tuna fishermen between the years 1994 and 2000. There were 292 recoveries (4.1%). This is a high rate in itself and valuable information was added, but it is obvious that trained scientific teams with top anglers and crews are more successful than the general public in properly applying tags. (One reason for non-return is probably mortality where a dead fish sinks or is eaten by sharks and the tag cannot be recovered.)
Some tags could record depth (through pressure) and location (by measuring the levels of light). Sunrise and sunset were the “most significant light events” and with an accurate electronic clock allow extremely precise east/west location and reasonable north/south estimates. It became apparent that Western tuna breed later in their lives than originally thought- another huge consideration in conservation and management.
Deep dives to over 500 fathoms (1000 meters) sometimes resulted in lowered internal body temperatures that experiments at the tuna lab showed to probably be the result of feeding on cold squid or fish living at those depths (Block fed captive yellowfins cold bait and measured cold internal temperatures.)
My question is “HOW DO THEY KNOW?” You can dive half a mile in most parts of the ocean and NOT find a meal!
In the field, the emotional highs and lows were enormous! The successful signal reception of the first pop-up tag started a major round of toasts and celebrations. Shortly after, on a rough and stormy night when the second pop-up tag failed to report in on its scheduled time, long faces abounded- until the weather eased and in calm water the tag sang like a bird to the overhead satellite. This alone allowed an adjustment, low tech but important, in additional buoyancy for subsequent tags.
Dr. Block was reduced to tears on the flying bridge one rough day when a large sea lifted the boat and one rudder hit and killed a tuna we were trying to tag. “I’m trying to save them- not kill them!” she sobbed.
The cooperation of anglers and crews, and their donations of time and money were an extremely important factor in the amazing success of this study and along with dozens of scientists and technicians all involved are to be highly congratulated! For more information get a copy of Science (17 August 2001). .
Recently, Paxson Offield was initiated into the IGFA Hall of Fame and a high light of his career and work in conservation was an ongoing program of PSAT tags in marlin. Currently, the internationally noted artist Dr. Guy Harvey is also a leader in not only tagging but other conservation initiatives.
We need people like Dr. Block, Dr. Harvey and Mr. Offield to help conserve our precious stocks of “Marine Megafauna”. AND we all need to do our part to help out.
See my next column in Marlin Magazine for a story of a Sportfishing CLUB gone BAD and becoming a detrimental group of swordfish killing amateur professionals.
Peter B Wright
For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit: www.guyharveysportswear.com
- Yellowfin Tuna Tagging in Panama
- John Lo Gioco Proves One Angler Can Make a Difference
- Canadian Bluefin Tuna
- Sailfish Mecca; Isla Mujeres Tagging Project
- Introducing Guest Blogger Peter B. Wright