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Commercial Fisheries News
Volume 36 Number 4
December 2008
Dogfish stock rebuilt; pup concerns linger
REHOBOTH BEACH, DE – A new scientific update on the status of spiny dogfish has concluded that the stock is fully rebuilt and overfishing is not occurring.
Technical experts reached this welcome finding after reviewing data from the Northeast Fisheries Science Center’s 2008 spring bottom trawl survey, as well as 2007 catch and bycatch information.
However, scientists continued to express concern about future biomass levels because very few small dogfish – the spawners of the future – were found in the current population.
The Atlantic States Marine Fisheries Commission’s (ASMFC) Spiny Dogfish and Coastal Shark Management Board was briefed about these findings during its Oct. 22 meeting in Rehoboth Beach. ASMFC dogfish technical committee member Jim Armstrong, who is also the Mid-Atlantic Fishery Management Council’s dogfish plan coordinator, presented the update.
Armstrong explained that the status of spiny dogfish is estimated in terms of mature females, referred to as the female spawning stock biomass (SSB).
To determine the SSB, scientists ran a calculation, known in technical jargon as a “stochastic estimate,” using the last three years of data on mature female dogfish.
The results put the SSB at 194,616 metric tons (mt), which is safely above ASMFC’s target of 167,800 mt – the level needed to classify the stock as rebuilt under ASMFC standards.
Furthermore, fishing mortality on dogfish was extremely low, coming in at 0.11, well below ASMFC’s threshold level of 0.39, which would trigger an “overfishing” designation.
Armstrong said, “There is virtually a zero probability that overfishing is occurring.”
Fed target higher
The New England and Mid-Atlantic councils, which jointly manage dogfish in federal waters, don’t have a biomass target approved by the National Marine Fisheries Service (NMFS). The councils originally submitted 180,000 mt as the SSB target, but NMFS disapproved that figure, deeming it too low and stating that 200,000 mt was more scientifically appropriate.
But many at the ASMFC meeting concluded the stock had met even this tougher 200,000 mt standard.
For one, 200,000 mt is pretty close to 194,616 mt, some said. And, prior to running the “stochastic estimate” of SSB, which “takes into account many sources of uncertainty,” scientists ran a much simpler equation, explained Armstrong.
This involved a straightforward three-year “moving average” of the female spawning stock based on the last three years worth of bottom trawl surveys. The calculation resulted in an SSB estimate of 218,000 mt.
“Just by looking at the survey catches, one could conclude that the stock is rebuilt,” said Armstrong.
Recruitment
Armstrong, however, tempered the good news. He stressed that scientists’ most significant concern about dogfish was the void of small fish in the population.
According to a draft report produced by the Northeast Fisheries Science Center’s Paul Rago and Kathy Sosebee, “The size frequency of the female population is concentrated between 75 centimeters (cm) and 95 cm with very few fish above 100 cm or below 70 cm.”
Assessment scientists see a particularly big dearth in the 40-to-60 cm size range, which is 16" to 24" in length, for both males and females.
As a result, they predicted there will be a drop in spawning stock biomass once again in a few years – even at the extremely low fishing mortality level of 0.11 – before the population takes another upturn.
“There’s not a lot to recruit into the spawning stock biomass in the future years,” said Chris Vonderweidt, ASMFC’s dogfish plan coordinator, who provided an overview of the dogfish technical committee’s position.
Pups an issue
Furthermore, said Armstrong, while biomass estimates of pups – dogfish less than one year old and less than 36 cm or 14-1/2" in length – have “definitely improved” from the stunning low levels witnessed between 1997 and 2004, they’re still “quite a bit” lower than historical levels.
“At the current level of spawning stock biomass we have now, you would expect the number of pups to be higher, so something else is going on,” he said. “Maybe the pup survival rate is not as high as it used to be.”
Part of the problem might be that mature females are smaller in size these days and may not be producing as many pups or ones that are as hardy.
According to Rago and Sosebee’s report, improved pup survival is key to achieving a biomass increase in the future following the expected downturn.
Massachusetts reacts
The Massachusetts delegation to ASMFC expressed frustration over the tone of the latest stock update.
David Pierce of the Massachusetts Division of Marine Fisheries said the report matched the “spooky” aura of Halloween, which was fast approaching at the time of the meeting. He called the report “full of fear” and “very precautionary.”
“The news of a fully rebuilt stock should bring great joy to everyone,” Pierce said.
Fellow board member Vito Calomo, who serves as proxy for ASMFC Commissioner and Massachusetts state Rep. Tony Verga, also stressed that “trumpets should be blowing” and people should be rewarded for the sacrifices made to fully rebuild the stock.
Following these comments, the board immediately moved to increase next year’s spiny dogfish commercial quota from 8 million pounds to 12 million pounds. See story page 6B for details.
Janice M. Plante
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