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Commercial Fisheries News
Volume 32 Number 6
April 2005
Research key to solving tuna/herring conflict
ROCKPORT, ME – Hoping that a fact-based discussion might ease tensions between bluefin tuna fishermen and herring midwater trawlers, the National Marine Fisheries Service (NMFS) assembled a panel of top-level scientists and others for a March 5 seminar at the Maine Fishermen’s Forum.
Armed with PowerPoint presentations, the panelists covered a wide range of topics, addressing everything from tuna distribution to water temperature to stomach contents.
By the end, no single factor had jumped out as the reason behind the recent precipitous decline of bluefin tuna availability in the Gulf of Maine. However, the experts agreed that carefully controlled cooperative research experiments could help resolve the matter.
It was clear from the outset that the vast majority of the standing-room-only crowd believed the lack of bluefin was directly related to the increasing presence of midwater trawlers in the region.
East Coast Tuna Association Executive Director Rich Ruais, a panel member, essentially summed up the audience sentiment with his opening statement.
“The transition of the herring fishery from traditional purse seine gear to midwater and pair midwater trawling in the mid-1990s has had a profound, negative impact on giant bluefin tuna fishing in New England,” he said.
Bluefin tuna harpooner Dave Linney of Cape Neddick, addressing the panel, said, “How do we convince you that there might be something to this anecdotal evidence? I’d do anything so you can see what we see out there every day.”
Solutions exist
Following the speakers, several fishermen called out comments without waiting to be recognized by moderator Steve Murawski of NMFS, who organized the seminar.
“Herring is a very, very big part of the recovery program for all fish,” said one fisherman. “Everyone paid a price for rebuilding and now everything is coming back. We need to work a little more on preservation of the bait. The last three or four years, there’s been no bait around.”
Murawski allowed everyone to express their positions but then told the crowd, “We can’t keep going back and forth with this ‘he said, she said.’
“These are solvable problems,” he insisted. “It’s a limited area in the inshore Gulf of Maine. There are lots of new technologies for tagging bluefin tuna. We can look at oceanography. We probably get more spatial information from the herring industry itself than anywhere.”
Murawski urged the audience to work on solutions.
“You need to put together a research program. It seems to me you’re going to need more information than you have on the table right now,” he said.
Mary Beth Tooley, executive director of the East Coast Pelagic Association and the member of the Maine Fishermen’s Forum board of directors who hosted the seminar, supported this approach.
“Our members are not interested in having a negative impact on herring for the tuna fishery,” she said. “I would encourage people to focus on the science and research priorities.”
Speakers
In addition to Murawski and Ruais, the other panelists were:
• Bluefin researcher Molly Lutcavage of the University of New Hampshire;
• Scientist Gerry Scott of the NMFS Southeast Fisheries Science Center; and
• Oceanographer David Mountain and scientist Bill Overholtz, both of the NMFS Northeast Fisheries Science Center.
Also in attendance was NMFS Director Bill Hogarth, who listened to the presentations and audience comments from beginning to end.
Bluefin shifts
Lutcavage has been tagging and tracking the migration patterns of bluefin for years with the help of industry. Her presentation looked at whether there have been big shifts in abundance and distribution of bluefin over the past two years.
She noted five areas of concern related to the New England fishery:
• The harpoon and purse seine “surface fisheries” have declined steeply in the past few years;
• Rod and reel catch rates have declined;
• Spotter pilots have seen fewer surface schools;
• Fishermen all around have seen fewer giants; and
• Bluefin tuna have been missing from traditional “hot spots.”
Possible reasons
Why these events have occurred isn’t clear, Lutcavage said, but she suggested several possible explanations, including: environmental and oceanographic variability; a change in the prey base; random shifts in the bluefin population; excess fishing mortality; or some combination of these factors.
Whatever the cause, Lutcavage said of the 2004 fishery, “We had a broader distribution of bluefin in the summer than in previous years. We had a lot of fish in the Mid-Atlantic Bight area, which was different. From Florida to Nova Scotia, the fish were spread out along the shelf break.”
She also said, “We believe we saw restricted distribution here in the Gulf of Maine.”
Oceanography
Scientists have been seeing changes in salinity and water temperature over the last decade, according to David Mountain, and the Gulf of Maine saw an increase in colder Scotian shelf water, even though water temperatures on the whole, and especially around Hatteras, have been warmer.
These factors have led to changes in convection and stratification, he said, which in turn could be having an impact on phytoplankton and zooplankton production.
“We’ve had some significant changes in the oceanography,” said Mountain. “How that affects what you’re looking at (bluefin tuna distribution and herring availability), we’ll have to see. We can look at the data bases we have.”
Herring expert Vaughn Anthony, now retired from the Northeast Fisheries Science Center, also made note of the plankton issue from his seat in the audience.
“We have seen some environmental changes and some fish changes,” he said. “Why are the herring offshore? Why don’t we see age 1 and age 2 herring inshore? It’s obviously a food problem or a temperature problem. I’d like to see you look at some Calanus stuff.”
Calanus, a genus of copepods, is considered to be possibly “the most important contributor to the annual zooplankton cycle” in the Gulf of Maine and on Georges Bank. It plays an extremely important ecological role and provides a critical food base for herring.
The text Fishes of the Gulf of Maine by Bigelow and Schroeder states, “In Maine coastal waters, diets of juvenile herring are varied but copepods are often the dominant prey, especially in summer.” The genus Calanus is cited as being particularly important to certain life stages at certain times of the year.
Temperature
Bill Overholtz said scientists had used acoustic surveys in recent years to help estimate herring stock size.
“By 2001, we had seen a tremendous aggregation of fish off Nantucket Shoals to Georges Bank,” he said. “Basically, we feel the offshore component of this resource has completely recovered and reoccupied its historical range.”
However, Overholtz then explained that herring are “very sensitive” to temperature and seem to seek out temperature zones in the 5°-7°C (41°-44.6°F) range.
In 2004, the water inshore was cool, he said, and the herring, following a more suitable temperature zone, were more offshore.
“Herring are good integrators of temperature and they can find what they need,” he said. “Temperature may be a major factor in why herring availability may change in the Gulf of Maine.”
Herring as prey
In the prey department, Overholtz said four groups of animals prey on herring: medium pelagic and bottom fish such as dogfish and cod; marine mammals; sea birds; and large pelagics such as sharks and tunas.
“When herring began to recover in the late 1980s, predators increased the percentage of herring in their diets,” he said.
“By far” the largest predator of herring is the first group – medium pelagic and bottom fish – followed by marine mammals, said Overholtz.
When the herring needs of all predators are combined, Overholtz said scientists estimate they consume on the order of 300,000 mt of herring. The herring fishery, on the other hand, utilizes roughly 100,000 mt, “about one-third of what the predators are taking,” he said.
Bluefin tuna “definitely have a herring component” to their diets, though it varies significantly by area, Overholtz said. In 2002, herring overall comprised about 18% of bluefin prey number-wise but 50% weight-wise, he said, and on Jeffreys, for example, the percentages were much higher.
Herring eat sand lance, squid, mackerel, and other species as well, but some note that there has been a decline in the availability of sand lance in the Gulf of Maine in recent years.
During her talk, Lutcavage emphasized that bluefin have been known to feed heavily in the Gulf of Maine.
“We see a big increase in perigonadal fat stores – up to 10 pounds – so they really put on energy stores when they’re up here,” she said. “The prey factor is something we all need to start paying attention to.”
Lutcavage’s recent studies indicate that herring is a dominant prey item for bluefin in almost all areas, and she said the prey issue raises important questions.
“You may have a biomass of prey but is it available to your predator? The availability of prey and density of prey is important,” Lutcavage said.
Bluefin not around
During his own PowerPoint presentation, Rich Ruais described what was happening to the bluefin tuna fishery from industry’s point of view.
In 2003, he said the fishery produced 530 metric tons (mt), down from 960 mt in 2001.
“During the 2004 season, we saw the worst production since the 1970s. It’s been described by some as a failure at a miserly 251 mt total catch,” he said.
The shift to midwater trawl gear for herring has “had the effect of greatly diminishing the early-season importance of tuna fishing,” said Ruais.
He called the midwater gear “too efficient” to compete with other fisheries that require “high concentrations of herring as forage.” Dense herring schools “attract and hold” tuna on fishing grounds, but midwater trawlers “intensively work nearshore fishing grounds until the catch rate is unacceptable,” he said.
According to Ruais, the problem is not one of bluefin abundance since fishermen in Canada and off North Carolina have been extremely successful in their own bluefin fisheries.
“All of Canada’s seven inshore bluefin fleets produced catches in 2003 and 2004,” he said. Furthermore, the “Hell Hole” fishery, less than 200 miles from the New England fishing grounds, was a top producer in 2003.
Following this rapid-fire presentation of information from all the speakers, audience members went straight to picking up on Ruais’ points, with several asking for an end to midwater trawling or the creation of an area off-limits to the trawlers.
“Give us a spot and watch what happens,” said Robert Fitzpatrick of Maguro America.
While the conflict essentially remained unresolved, Ruais said one thing researchers could do is get together with Canadian scientists to develop one common herring biomass estimate. Currently, the Canadian estimate for the size of the resource is significantly lower than that of the US.
Mary Beth Tooley asked everyone in the room to avoid jumping to unfounded conclusions.
“Herring are very temperature oriented,” she said. “If the temperature is not right, they’re not going to hang around. I would ask people to think about the information that was presented today.”
Steve Murawski closed the session by strongly urging industry members to conduct cooperative research.
“If you really want to solve this problem, you need to find a venue to get this research kicked off,” he said.
One fisherman called out a parting remark to the panelists.
“Don’t take us being emotional with meaning that we’re not appreciative you’re all in the room,” he said. “We want to talk with you.”
Lorelei Stevens
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