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Commercial Fisheries News
Volume 33 Number 11
July 2006
TRAC reports herring complex in good shape
NEWPORT, RI – The Gulf of Maine and Georges Bank Atlantic herring stock complex is at a high level of abundance and fishing rates on the overall resource are at extremely low levels.
That’s the conclusion of the joint US/Canada Transboundary Resource Assessment Committee (TRAC), which met May 2-5 in Woods Hole, MA to update the status of the herring stock complex.
“We’ve made great progress in assessing this resource in the past few years,” said Bill Overholtz of the National Marine Fisheries Service (NMFS) Northeast Fisheries Science Center, who led the US team of TRAC scientists.
“We reached full consensus on these results,” he said. “I think the herring stock is in good shape and I’m pretty encouraged by the results of the TRAC.”
Overholtz made these comments during a June 14 presentation to the New England Fishery Management Council in Newport.
The previous TRAC, held in 2003 in St. Andrews, New Brunswick, caused a considerable stir after Canadian scientists found the resource to be at a significantly lower level of abundance than US scientists. The two teams had used different models to assess the stock and could not agree on the results.
But this year, scientists from both countries used the same ASAP model, which is “an age structured forward projection model with flexibility to address fishery selectivity, stock recruitment, and constraints on virgin biomass, steepness, scale, and other factors.”
And the results were far more definitive. According to the TRAC’s consensus report, the overall biomass of age 2+ herring in 2005 was roughly 1 million metric tons (mt) strong, and three “very large year classes” were produced in 1994, 1998, and 2002.
“These year classes have really driven the recovery of this stock,” said Overholtz.
Furthermore, the TRAC determined that the overall fishing mortality rate was 0.1.
In fact, said Overholtz, “The fishing rate in 2005 was the lowest in the 1967-2005 time series.”
New reference points
As part of this recent assessment, the TRAC developed new biological reference point estimates for herring. Here are the new numbers compared to the “proxy” or “placeholder” reference points used in Amendment 1 to the federal herring plan:
Maximum sustainable yield (MSY) – 194,000 mt vs. the old proxy of 220,000 mt;
Bmsy, which is the stock biomass that would produce MSY at a fishing mortality rate equal to Fmsy – 629,000 mt vs. 1,100,000 mt; and
Fmsy, which is the fishing mortality rate that would produce MSY – 0.31 vs. 0.2-0.25.
“Based on these reference points, the stock is fully recovered and overfishing is not occurring,” said Lori Steele, the New England council’s herring plan coordinator.
Steele also told the council that the old proxy reference points listed in Amendment 1 would be automatically updated to reflect the results of the TRAC. The amendment is expected to be implemented in time for the Jan. 1, 2007 start of the next fishing year.
Several council members questioned the new numbers since the biomass reference points were lower than the old numbers and the fishing mortality reference point was higher.
But Overholtz said, “These are the first numbers we have that come out of an assessment and to me these are the appropriate numbers.”
Of the Bmsy number, he said, “This is a really solid estimate for this stock complex.”
Inshore component
The Atlantic herring resource is still assessed as one large stock complex because the full degree of mixing between the various stock components has yet to be conclusively pinned down.
“This has been a thorny issue for the herring committee for quite some time,” said David Pierce of Massachusetts, who chairs that committee for the New England council.
According to Pierce, the committee would like to have a better understanding of the inshore stock component, especially given the concern for Area 1A in the inshore Gulf of Maine, which is the most heavily fished of all stock areas.
“The inshore component is extremely important for us to understand,” said Pierce.
While it didn’t conduct a separate assessment for the inshore population, the TRAC this year developed an estimate of the “relative proportion of the inshore component within the overall herring stock complex.”
The number turned out to be 18%, meaning the inshore population makes up 18% of the stock complex.
The TRAC looked at three different data sources and then took the average of the three to calculate the 18%. The TRACs summary report identifies the data sources as follows:
“Commercial acoustic estimates of biomass during 1999-2000 suggested that the average proportion on the inshore component was about 10%.”
“Morphometric analyses of four samples of herring obtained during 2005 in the winter fishery area from Long Island to Martha’s Vineyard indicated an average inshore population of about 13%.” (Morphometric studies look at the physical differences between fish – things like length from eyes to mouth, distance from eyes to dorsal fin, and other factors – to differentiate stocks.) And
“Swept area biomass estimates from the NMFS autumn survey estimated the inshore component to be about 30% of the total complex.”
Council members asked whether the TRAC had put more emphasis on one data source over another. Overholtz said no. The three sources were not weighted to give any one source a higher priority.
“There is some variability in the estimates, but the TRAC felt this was the way to go,” he said.
Predatory/prey
Many council and audience members who listened to Overholtz’s presentation asked several questions about natural mortality on herring and predator/prey relations.
Overholtz said the TRAC used a rate of 0.2 as its estimate for natural mortality, which scientists concluded worked well. Natural mortality is a measurement of the rate of death from all causes other than fishing, such as predation, disease, starvation, and pollution.
“That’s consistent with the life history of herring,” he said.
Overholtz also explained that scientists were putting additional effort into estimating the consumption of herring in the diets of predators and calculating how these predatory/prey relationships have changed over time.
For example, “More herring are showing up now in the stomachs of cod and spiny dogfish,” he said.
Ongoing studies are tracking herring consumption by the following four predator groups:
Medium-sized fish, which include cod and dogfish;
Highly migratory species like bluefin tuna and various sharks;
Marine mammals; and Sea birds.
“We’re trying to get an overall view on consumption of herring by those groups and determine the impact that would have on herring and on us,” said Overholtz. “We’ve made some progress there.”
Bottom line
Overholtz did point out that the ASAP model used in this new assessment exhibited a “retrospective pattern.” That means it tended to overestimate abundance and underestimate fishing mortality in the most recent years – a problem associated with numerous stock assessment models.
When several council members expressed concern over this factor, Overholtz several times gave assurances that it shouldn’t be a problem given the large size of the stock and the extremely low fishing mortality rate.
“I don’t think it’s a cause for concern unless we go to a high fishing rate,” he said.
In conclusion, Overholtz said, “The herring complex is really in pretty good shape. We have a very high biomass. Fishing rates are low. On average, recruitment has improved greatly and it’s going to provide us with a lot of options in the future. We have good research initiatives ongoing with tagging studies and morphometric studies. I think we’re going in a good direction.”
What’s next?
The New England council’s herring committee and industry advisers were scheduled to meet on July 6 in Portland, ME to further review the TRAC results and develop preliminary herring specification recommendations for fishing years 2007 through 2009, including area-specific total allowable catch (TAC) recommendations.
Steele told the council on June 14 that the herring PDT would not be making any recommendations for changes in the area-specific TACs.
“It’s important to fully understand that the TRAC assessment does not address management area TACs,” she said.
Based on the new biological reference points and the fact that the resource overall is not overfished and overfishing is not occurring, Steele said, “The PDT has no technical basis or new information to recommend any specific changes to the TACs at this time, so any changes the council wants to make will be a policy call.”
In its written report to the council, the PDT stated that “recent levels of removals” – meaning those over the past 15 years – “appear to be sustainable.”
The PDT advised, “The council should provide adequate justification/rationale should it wish to consider any major changes to the area-based TACs for the 2007-2009 fishing years as such changes will be based primarily on allocation and not a specific biological need.”
Janice M. Plante
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