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Commercial Fisheries News
Volume 33 Number 1
September 2005
Tagging work reveals yellowtail behavior
NEFSC photos
WOODS HOLE, MA – Sure, everyone knows that yellowtail flounder live on the ocean floor and fishermen use flatfish nets to catch them.
But new tagging information has revealed something rather remarkable. Yellowtail actually come off the bottom at night, often around sunset, usually for four hours or so. And it’s not a rare phenomenon. They do this practically on a daily basis.
“Some fishermen have known this happens,” said Dave Martins of the School for Marine Science and Technology (SMAST) at the University of Massachusetts-Dartmouth. “But they’re surprised at how often it occurs.”
The ritual rising is now well documented thanks to extensive tagging work carried out cooperatively by scientists and fishermen.
The work began in 2003 as a pilot project. In 2004, it became a full-scale operation. And in 2005, project partners, who completed their last tagging trip in early August, went a step further and conducted an additional cage study to be sure the tags themselves weren’t causing increased mortality.
All told, over 35,000 yellowtail flounder have been tagged – most with bright pink, yellow, or orange disks.
But 556 of the fish have been outfitted with archival data storage tags (DSTs). The DSTs, which look like little circuit boards and are about the size of a paper clip, are mini data loggers that record water temperature and pressure every 14.7 seconds.
So far, 42 DSTs have been returned to the Northeast Fisheries Science Center in Woods Hole, which is overseeing the project.
Those 42 units housed the information that allowed scientists to confirm the unexpected nighttime off-bottom behavior. Every one of the DST-tagged fish exhibited the same pattern. Night fell, and up they went in the water column.
“This is pretty definitive,” said project leader Steve Cadrin of the science center.
“It changes the way we think about the whole population structure and how the fish move,” he said.
According to Martins, discoveries such as this one really draw fishermen into the tagging work.
“These are the things they’re interested in knowing and learning about,” he said.
Cadrin agrees and appreciates the feedback he’s received from industry members who have theories about why this nightly behavior occurs. Speculation ranges from feeding to predator avoidance. Many believe the rising is related to the lunar cycle, which affects tidal patterns.
“It’s amazing to talk to the guys about this,” Cadrin said.
Of the 133 data storage tags placed on fish in 2005, all were deployed in or near Closed Area II. Taggers wanted to flood the area with DSTs to get a handle on fish behavior on what’s known to be prime yellowtail bottom.
Keep the pink tags too!
While most fishermen have come to appreciate the extraordinary value of data storage tags, the devices are, unfortunately, very expensive, running close to $200 per piece.
That’s why project coordinators primarily use plastic disk tags. They’re cheap yet they still provide valuable information about fish movement. Just knowing the release site of a fish, its size at release, the recapture site, and its size at recapture has provided a wealth of new information that’s helping scientists better understand migration patterns, stock mixing, mortality, and much more.
Azure Westwood is a biologist who’s been contracted by the science center to coordinate the yellowtail tagging trips and recapture information. She said that as of early August, 1,884 tags had been returned. Most were returned by fishermen, but some came from processors, observers, and biologists as well.
Take scales
This year, project organizers tried something new. Of the 7,000 fish tagged this summer, nine percent were outfitted with orange disks on their underside.
Orange tags signal a request for scale samples. Anyone catching an orange-tagged yellowtail should scrape a few scales from the fish. Return the scales, along with the tag and pertinent recapture information, to the science center where they’ll be compared to scales taken from the fish at the time of tagging.
“We’ve gotten back 36 fish so far from the scale work,” said Westwood.
According to Cadrin, the scales are important because they will help scientists get a better handle on aging.
“One of the suspect sources of uncertainty in our stock assessments is growth,” said Cadrin. “There seems to be a lack of older fish in the population so we want to ask ourselves, ‘Are we aging these fish appropriately?’”
In addition to this year’s orange disks, some of the pink disks released in 2003, 2004, and even 2005 also carry requests for scale samples.
Tag returns key
The success or failure of the tagging work is directly tied to fishermen’s willingness to return tags, and the New Bedford fleet in particular has been “just super” about following through.
Westwood and Cadrin both credit three SMAST people – Dave Martins, Darin Jones, and Ross Kessler, who now works for the commonwealth of Massachusetts – with gathering and returning a total of 229 tags as of Aug. 1. This represents 12 percent of all tags returned.
“They do a lot of outreach work for us in New Bedford,” said Cadrin. “They’re true partners in this.”
Martins, who regularly stops by the docks before work to see what’s going on, speaks Portuguese, which has helped him develop strong ties in the community. While he’s out and about, fishermen sometimes give him a shout, directing him to the boat. Then they’ll hand over a tag, and Martins takes care of the rest.
“At the beginning, some boats saved me the whole fish with the tag still on it,” Martins said. And then he’d get a good length measurement on the fish and sex it.
But now that fishermen are more familiar with the project, they typically just save the tags and supply key facts about where and when the fish was caught and, if possible, the length and condition of the fish.
According to Martins, the majority of the fleet thinks the tagging work is “a good thing.”
“Fishermen are always interested in where the fish are going and where they came from,” he said. “If anything, they think this should have been done a long time ago.”
During 2003 and 2004, SMAST conducted seven of the tagging trips, which, all told, were responsible for putting out 2,709 tags, including 98 DSTs.
With the 2005 tagging trips completed, project organizers are setting their sights on next year’s work.
At a May 2 yellowtail tagging meeting in Woods Hole attended by representatives from industry, SMAST, the science center, the Northeast Consortium, state agencies, and other institutions, participants agreed to deploy any available 2006 data storage tags in the Great South Channel, assuming funds become available.
“This is the crossroads of all three stock areas,” said Cadrin while explaining the significance of the Great South Channel.
Besides the regular stock-wide tagging effort planned for 2006, participants also concluded that an additional 1,000 disk tags – imprinted with a unique number series – should be deployed just in the Nantucket Lightship Closed Area. These will be used to track and study yellowtail movement in and around the area.
Photo library
SMAST has additional work planned for the future as well.
According to Martins, SMAST photographed 1,061 individual yellowtail during the 2003 and 2004 trips, which accounted for roughly 39 percent of the SMAST-tagged fish.
Martins is hoping the photo library will provide valuable information about the fish themselves once the images are analyzed.
“We want to try to study whether there are different characteristics between males and females, and whether the fish have different body shapes and color depending on where they’re caught,” said Martins.
“We think this is the first time anyone’s tried to do this,” he said.
Janice M. Plante
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