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Commercial Fisheries News
Volume 36 Number 10
June 2009
New lobster assessment reveals stock nuances
ALEXANDRIA, VA The status of the American lobster resource hasn’t changed a whole lot over the past three years at least not at first blush.
According to the new 2009 stock assessment, the Gulf of Maine and Georges Bank stocks are still in “favorable” condition except for statistical Area 514 in the Gulf of Maine while the Southern New England stock remains in “poor” condition. That’s about how things stood when the last assessment came out in 2006.
But underneath those generalities, the 2009 assessment, which was run with a new model developed by Yong Chen and colleagues at the University of Maine, revealed a wealth of detailed information, showing both big and small changes in everything from effort and abundance to recruitment and sex ratios.
The model also indicated that overfishing was not occurring on any of the region’s three lobster stocks, even in Southern New England, where the stock is at low abundance and effort has dropped considerably.
The Atlantic States Marine Fisheries Commission’s (ASMFC) American Lobster Management Board, which heard the assessment results during a May 5 meeting here, said it wanted time to take in the latest findings. However, the board also said it planned to gather again in August to consider potential management responses.
The assessment, roughly two years in the making, was conducted by a subcommittee of ASMFC’s American Lobster Technical Committee, which was chaired by Kim McKown of the New York State Department of Environmental Conservation’s Bureau of Marine Resources.
The completed assessment was scrutinized by a peer review panel of independent scientists.
Review panel member Tom Miller of Maryland, who was on hand for the May 5 board meeting, publicly congratulated the stock assessment subcommittee for its work, which he said was extensive and well done.
“Generally, the assessment is the best available science and provides a sound foundation for management,” he said.
Gulf of Maine, 514
Here are the 2009 assessment’s basic conclusions.
The Gulf of Maine stock in general is at record high abundance despite record high effort a phenomenon that remains a complete “conundrum” to scientists. The stock is not overfished or depleted.
As in the previous 2006 assessment, the one exception is statistical Area 514, which encompasses Massachusetts Bay and Stellwagen Bank. According to the assessment subcommittee, this part of the Gulf of Maine continues “to experience very high exploitation rates and declines in recruitment and abundance.”
Regarding Area 514, the subcommittee concluded, “Restrictions are warranted given the persistence of low recruitment and its negative effect on total abundance and egg production potential.”
Georges, SNE
For Georges Bank, the subcommittee found that “current abundance is at a record high compared to the 26-year time series, and recent exploitation rates are at a record low.” The stock is not overfished or depleted.
According to the subcommittee, only 5% of the region’s lobster landings come from the Georges Bank stock. And, for unknown reasons, the sex ratio on Georges is heavily skewed toward females, with females making up roughly 80% of the population. Scientists expressed concern about potential future problems if females become “sperm limited.”
The Southern New England stock, as many feared, remains “depleted,” even though effort is low and overfishing is not occurring.
Landings bottomed out in 2004 and, despite a small up-tick, continue to bump along at very low levels. Abundance is the lowest observed since the 1980s.
The assessment subcommittee said, “Given current low levels of spawning stock biomass and poor recruitment, further restrictions are warranted” for Southern New England.
Two models
According to scientists, the key to any good stock assessment is the input of good data.
The 2006 stock assessment suffered from numerous data problems, but both McKown and Miller said the “data situation had improved significantly” for the 2009 assessment, even though some gaps remained.
Maine in particular has made several regulatory changes in recent years to collect more trip-level information directly from lobstermen, which has resulted in better assessment data coming from the state.
McKown and Miller presented details about how the University of Maine model worked. They also talked about the secondary model used in the assessment the Collie-Sissenwine model.
Back in 2006, the Collie-Sissenwine model was the primary assessment tool, but in 2009, the model was run more as a back-up to the University of Maine model.
Researchers have been developing the University of Maine model for a decade and its use is strongly supported by Maine industry members who have followed its progress. It is a statistical “catch-at-length” model that uses multiple sources of information, including lobster lengths during many different life stages.
The Collie-Sissenwine model is simpler. It uses an equation that estimates changes in abundance during two life stages pre-recruits, which are lobsters that will molt into legal size during the year, and fully recruited animals, which already are legal size in response to recruitment, natural mortality, and fishery removals. It does not use length information and it does not use information from as many at-sea surveys as the University of Maine model.
Both models “useful”
Miller said the review panel supported the assessment subcommittee’s primary use of the University of Maine model, which was “more rigorous and reliable.”
However, Miller said the panel urged ASMFC to continue using the Collie-Sissenwine model as a secondary indicator of the status of each stock.
“We believe it continues to provide useful information, even though it’s probably less capable of detecting abrupt changes in the stock,” he said, adding that the “trend” in assessment science is to use more than one model.
Different results
The two models, however, produced different results.
While the University of Maine model concluded that overfishing was not occurring on any of the region’s lobster stocks, the Collie-Sissenwine model concluded that overfishing actually was occurring on all three.
“The results are very different from the University of Maine model,” acknowledged McKown to the ASMFC lobster board.
This difference troubled several board members, who asked questions about both models and wanted to know each could produce such different bottom lines.
The reason, McKown and Miller explained, is that different information was used to run each model.
Reference points
Next came the complicated matter of reference points the “threshold” and “target” numbers used to gauge whether or not a stock is overfished or if overfishing is occurring.
ASMFC’s current lobster reference points were adopted back in 2006 when the Collie-Sissenwine model was the primary assessment model.
The 2009 assessment subcommittee recommended new reference points that use different thresholds and no targets for “median reference abundance” and “median effective exploitation.” Roughly speaking, “median” means the “middle” point, not the average.
The abundance thresholds were developed using median population estimates of all male and female lobsters combined greater than 78 millimeters (slightly larger than 3-1/16”) for the years 1982-2003 for the Gulf of Maine and Georges Bank and 1984-2003 for Southern New England.
The subcommittee then compared average abundance and effective exploitation rates for males and females combined for 2005-2007 and compared those to the new threshold numbers.
This is how the subcommittee determined that the Southern New England stock was depleted: recent abundance was below the median reference abundance level.
Third set
The subcommittee’s recommended reference points, however, can’t replace the 2006 numbers used with the Collie-Sissenwine model until ASMFC formally approves a new addendum to the interstate lobster plan.
And, as it turned out, the peer review panel rejected the subcommittee’s recommended reference points and instead recommended a set of its own.
Under the review panel’s less stringent threshold levels, the Southern New England stock would not be considered depleted.
After the review panel made its position known, McKown said the assessment subcommittee discussed the situation via conference call.
During the call, the subcommittee reached a consensus. It did not agree with the review panel on the reference point issue. Instead, it decided to stand firm on its own reference point recommendations.
“We support the panel’s advisory report except for their recommended reference points. We just don’t think they’re precautionary enough,” McKown told the board.
Board reacts
After hearing all that, lobster board members sat back to consider how to proceed given that they now had three very different and conflicting sets of reference points. And, although the University of Maine model was the primary assessment tool, the board still had to consider the different conclusions between that model and the Collie-Sissenwine model.
“I think we need to mull this over a little,” said board member Mark Gibson of Rhode Island.
“I think the primary issue is the Southern New England region. This is very serious, and my sense is that we’ll need to configure a response to rebuild that stock,” he said.
Gibson didn’t rule out consideration of action for the Gulf of Maine either.
“I think the Gulf of Maine has issues as well because of the discrepancy in the two models,” he said.
Board member Dave Simpson of Connecticut echoed Gibson’s concerns for Southern New England.
“I think the Southern New England area needs a very close look as to what’s necessary for a regulatory response,” Simpson said. “We’re going to have to look at ways to keep this stock from completely collapsing to the point where it won’t support a commercial fishery.”
Maine Commissioner George Lapointe said he, too, wanted time to digest the new assessment information and “talk with people back home,” including Maine lobster biologist Carl Wilson, who served on the assessment subcommittee. Lapointe said he intended to ask the question, “What would you challenge us to consider to move this fishery ahead?”
The board charged its technical committee with developing additional guidance and recommendations for consideration in August. Then, the board will decide whether it wants to adopt new reference points and/or take action for one or more stocks based on the 2009 assessment findings.
Janice M. Plante
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