Modern tags boast a variety of styles and functions. Some tags are surgically implanted. They archive information on animals' whereabouts, behaviors, and environments until the critters are caughtusually accidentally, by fishers. The fishers, alerted by a label streaming from the animal's body, remove the tags and return them to researchers for analysis.
Other tags are designed to hitch a ride on an animal for up to a year. At a designated time the tags pop off, float to the surface, and relay, via satellite, the details of the animals' journeys back to researchers.
The newest types of tags are attached to things like shark fins and sea turtle shells. Whenever above water, the tags phone home via satellite.
Knowing which type of tag to use comes through trial and error. "For each species you have to learn what works best," Block said. For example, pop-off tags tend to detach prematurely from fast-moving animals and so are not as effective for them as implanted, or archival, tags.
The problem with archival tags is that more than half of them are never returned, so researchers must implant them on a high number of animals. The success of archival-tag technology depends on partnership between researchers and commercial fishers. Often researchers will pay a reward of up to U.S. $1,000 for the return of a tag.
Cost is the other factor when it comes to deciding which type of tag to deploy.
Archival tags are a relatively cheap U.S. $1,300 each but have a low recovery rate. Pop-off tags are about $3,800 each, when the cost of satellite time is included. But, in Block's experience at least, they have an 85 percent recovery rate. The newest tags, called smart-position and temperature-transmission tags, run about $4,000 for 18 months of data, including satellite time.
"On average the work is expensive, but then we have the opportunity now to get information that will lay the foundation for the future management of these very important species," Block said.
Block began using the tags for marine research a decade ago in the North Atlantic, deploying archival and pop-off tags on bluefin tuna to document their migrations from the eastern seaboard of the United States across the Atlantic Ocean to the Mediterranean Sea.
Before the research, fisheries managers thought the tuna were homebodies and managed the species as having two distinct populationsone in the eastern Atlantic and the other in the western Atlantic. The new information changed management guidelines for the bluefin fishery, the most lucrative in the ocean.
As they field-test new tagging technology and ramp up the ability to properly integrate the collected data with computer models, CoML researchers are already beginning to collect new information on the oceans.
Recent insights include how different tuna species divide up the North Pacific Ocean, how elephant seals migrate from California to Alaska, and how loggerhead sea turtles, tuna, and swordfish share underwater "highways."
By mapping the new data, researchers hope to learn how to keep the animals alive without destroying the fishing industry.
"I see the [researcher-fisher] partnership here as developing ways to collect high-resolution data and new ways to analyze data, so scientists can better understand what is going on, so managers can make better decisions," said Crowder.
SOURCES AND RELATED WEB SITES