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Commercial Fisheries News
Volume 35 Number 3
November 2007
Assessment: Scallop stock in good shape overall
PLYMOUTH, MA – A new stock assessment for Atlantic sea scallops has concluded that the resource overall is not overfished and overfishing is not occurring.
Landings, which averaged about 26,000 metric tons (mt) of meats – or 57.2 million pounds – from 2002 to 2006, have been at historical peaks. Biomass is high and the Mid-Atlantic has supported some exceptionally good recruitment in recent years.
Jim Weinberg of the National Marine Fisheries Service’s (NMFS) Northeast Fisheries Science Center reported this extremely positive news to the New England Fishery Management Council on Sept. 19.
“This is a real success story,” he said.
Weinberg and others attributed much of the success to the council’s rotational area management program, which is strongly supported by industry.
“Landings have really increased in this fishery,” said Weinberg.
The stock assessment was conducted by independent scientists from North Carolina, Canada, and Australia who agreed to serve on the 45th Stock Assessment Review Committee (SARC) for scallops.
According to Weinberg, the SARC used a new model called CASA to carry out the assessment.
CASA stands for “catch at size analysis,” meaning the model uses size – shell height – from scallops in both commercial and survey catches instead of age, which is often used in other stock assessment models.
Using the CASA model, the team came up with new biological reference points for the stock based on updated growth and size selectivity information. The revised size selectivity information accounted for the shift toward larger scallops in landings.
Biomass
The SARC recommended a new biomass “target” of 108,600 mt of meats and a new “threshold” level – the number you don’t want to drop below – of 54,300 mt of meats. Biomass is calculated using scallops greater than or equal to 40 millimeters (mm) in shell height.
The biomass in 2006, said Weinberg, was estimated to be 166,000 mt of meats – or 365.2 million pounds – well above both reference points.
The assessment models focused on Georges Bank and the Mid-Atlantic. The Gulf of Maine and Southern New England, which the SARC said contribute little to landings or biomass, were not included.
Fishing mortality
As for fishing mortality, the SARC proposed a new overfishing threshold of 0.29, which compares to the current overfishing threshold of 0.24.
During fishing year 2006, the actual overall fishing mortality rate was 0.23, meaning that overfishing was not occurring.
But that’s because fishing mortality, which is based on fully recruited scallops greater than 120 mm shell height, was combined for the entire scallop region.
Independently, fishing mortality on Georges Bank was 0.31 – over both the current and new thresholds – and in the Mid-Atlantic it was 0.17 – well below both thresholds.
The overfishing target – the safer number to be at – is 0.20. SARC scientists did not revise this target, and the New England council is proposing to keep it in place in Framework Adjustment 19.
Much more data
This latest stock assessment incorporated much more data – and different kinds of data – into the calculations than previous assessments.
Besides traditional NMFS survey data, the new CASA model used information from underwater camera video surveys conducted by the School for Marine Science and Technology (SMAST) at the University of Massachusetts Dartmouth, as well as commercial landings data, shell height measurements from landed scallops from port and sea sampling, catch per unit effort data, and growth rate information.
According to Weinberg, SARC scientists supported using the additional data.
“They felt this was a big improvement,” he said.
Recruitment
The news about recruitment was a little mixed.
“Total recruitment has been higher since 1996,” said Weinberg. “The Mid-Atlantic has had very high recruitment events in recent years, but there’s a little concern about recruitment on Georges Bank being a little below its average.”
Sea scallop recruits correspond roughly to two-year-old individuals, said the SARC.
Despite recent lower recruitment on Georges, the bottom there is still presently supporting a good number of scallops.
“About half of the biomass is in the Mid-Atlantic and half is on Georges,” reported Weinberg.
The SARC noted that three-quarters of total landings from 2000 to 2005 came from the Mid-Atlantic Bight, but in 2006, Georges Bank accounted for two-thirds of total landings.
“The shift in 2006 was due to low landings in the Hudson Canyon Access Area in the Mid-Atlantic combined with high landings in the Georges Bank access areas,” explained the SARC.
Years ahead
Given the size of the biomass overall and the recent good recruitment in the Mid-Atlantic, the future looks promising for scallopers.
“The stock is expected to remain pretty stable,” said Weinberg.
In its assessment summary, the SARC added, “Projections with fishing mortality rates of 0.20 and 0.24 per year suggest there will be modest increases in biomass and landings during 2006-2009.”
However, the SARC did caution that “projection results are uncertain.”
Janice M. Plante
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