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Commercial Fisheries News
Volume 35 Number 9
May 2008
Tag data: Dogfish swim far, fast, very deep
BIDDEFORD, ME – Groundbreaking new research into dogfish migration patterns is producing some jaw-dropping preliminary results.
With the help of a satellite pop-up tag, researchers at the University of New England were able to track the swimming activity of a female dogfish for roughly three months. The tag, attached to the fish’s dorsal area, released itself and “popped up” on Feb. 2, transmitting its accumulated data via satellite.
After sorting through the data, researchers discovered that this single fish covered enormous ground – at one point traveling from Canada’s Bay of Fundy down to Virginia in six weeks. She traveled inshore, offshore, north, south, back north, back inshore, back offshore, and around in loops in what was, by all accounts, a surprisingly short period of time.
This one fish defied all the old dogma about dogfish.
A second satellite tag from a different dogfish popped up on Jan. 31. While researchers hadn’t filtered through all the data yet to determine where this fish had traveled, they did have a chance to plot the accumulated information about depth.
And as it turned out, this second dogfish swam deeper than anyone previously imagined – down to 700 meters, or roughly 2,310 feet. She stayed at that depth for a week at a time on two occasions and, in all likelihood, was cruising along with other females.
“These things are traveling great distances vertically and horizontally,” said James Sulikowski, an assistant professor at the Biddeford-based University of New England who is heading up the research.
Sulikowski presented these and other early findings to roughly 50 commercial and recreational fishermen at a special March 29 dogfish forum held at the university’s campus.
The forum was co-organized by Sulikowski, commercial industry representative Jay Allocca of Vessel Services Inc., recreational industry representative Mike Jancovic of Maine River and Sea Charters, and Phil Grondin of South Portland’s Sturdivant Island Tuna Tournament.
Too deep to catch
Other speakers presented information about dogfish management, the status of the stock, and their own ongoing research (see related stories).
But the charts showing the track line and extraordinary depth profile of these two separate female dogfish are what had fishermen on the edge of their seats.
“So this means if the trawl survey is towing at the top (of the water column) when the fish are at the bottom, they won’t catch any of them,” called out one fisherman.
Throughout the morning-long forum, many in the audience questioned the validity of the National Marine Fisheries Service’s annual trawl survey results for dogfish and asked why the agency wasn’t taking into account how deep and far these fish were traveling.
Sulikowski emphasized that the data he presented was preliminary and only from one dogfish for the track line chart and one dogfish for depth profile chart.
“This data is all new. It wasn’t available before. We still need to look at the data much more closely,” he said, adding that additional tagging work needed to be conducted.
Nonetheless, Sulikowski conceded that even these early findings should lead people to begin thinking about dogfish “in a different way than in the past.”
Three tagged fish
Traditional tagging using devices like spaghetti tags is easy and cheap, but someone has to recapture the fish in order for scientists to get data. Even then, the data only show where tagged individuals were released and where they were recaptured.
In an effort to obtain more detailed information on migration patterns, Sulikowski’s research team decided to use pop-up satellite tags even though they are extremely expensive.
They picked the smallest pop-up tags available on the market, which were priced at $4,200 per tag. And then they had to kick in an additional $500 per tag to cover satellite time.
The team had enough money to tag three fish – one on Oct. 31, 2007 and two on Nov. 7, 2007.
Although two of the three satellite tags had “popped off” and transmitted their data as of late March when the crowd was gathered for the dogfish forum, the third was still at large, hopefully still attached to a swimming dogfish and continuing to collect data.
Depth, location, temps
Sulikowski wasn’t yet prepared to present information about the second tagged dogfish’s travel path, but he did say the fish appeared to spend a considerable amount of time running north and south between New Jersey and North Carolina, with one quick jaunt to Florida.
The tags collect depth, location, and temperature readings every hour while attached to the fish and then transmit the data to the satellite once they pop off the fish and rise to the surface.
However, the tag has a considerable amount of stored information that isn’t fully transmitted to the satellite, which is why researchers desperately want to retrieve tags that have popped up and are now presumably floating around at sea.
Although it’s a little like looking for a needle in a haystack, the University of New England team remains hopeful that someone somehow will find and return one of the dogfish pop-up tags. The reward is $250 and the contact info is printed on the tag itself.
Why so deep?
The age-old dogfish paradigm goes like this: In the summer they’re in the north off New England, and in the winter they’re in the south off the Mid-Atlantic.
“So why do we catch them in the Gulf of Maine year round?” asked Sulikowski.
This is one of the questions researchers hoped to answer through the tagging work.
And while no one should draw any final conclusions from one tagged fish, the track line for the tagged female that ran from Canada to Virginia in six weeks and then headed north again, offshore, south, and in circles in November, December, and January clearly disputes that old thinking.
Furthermore, what was the second fish doing at such enormous depths? This female spent a considerable amount of time at around 200 meters, but she clearly spent time at much deeper depths down to 700 meters.
Sulikowski said other researchers studying shark species such as porbeagles and makos have recorded similar phenomena.
“There is clearly something going on at this depth,” he said.
However, much more research is needed to determine if that “something” is feeding, mating, resting, or something else altogether.
“Fish usually move for two reasons – feeding and reproduction,” Sulikowski said.
More work
Fishermen in the audience asked why there wasn’t more research like this being conducted.
“It takes a lot of time to do something like this,” said Sulikowski.
And at roughly $5,000 a whack for one pop-up tag plus satellite time, money always is a significant complication.
But as costly and time consuming as the work so far has been, Sulikowski believes it’s all worthwhile.
“Without this kind of information, we’re not going to think outside the box,” he said.
Janice M. Plante
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