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Commercial Fisheries News
Volume 35 Number 9
May 2008
There’s no season; dogfish produce pups all year long
BIDDEFORD, ME – Most fish species have a distinct spawning season. Cut open a bunch of female cod in June from Georges Bank and chances are that most of those fish will be in just about the same spawning condition.
Not so with spiny dogfish. Researchers from the University of New England here recently cut open 50 randomly selected females harvested in December. And, to their astonishment, all the fish were in different stages of gestation. Some of the pups were tiny – essentially all yolk-sack – while others were just about fully developed. The same was true for females harvested and cut open during previous months.
“I think this is one of the most interesting things that could be going on here with dogfish,” said James Sulikowski, an assistant professor at the university’s Marine Science Center.
During a March 29 forum at the university’s campus in Biddeford, Sulikowski said most sharks – as well as most fish – have distinct reproductive cycles where individuals within the same species mate and spawn at right around the same time.
“Dogfish do not appear to be following that same cycle,” he said. “From what I can tell, they’re asynchronous.”
Dogfish are thought to have a 22-month gestation period. That’s a long time for females to carry pups. But if dogfish were synchronous in their reproduction cycles, they’d all be giving birth at about the same time after carrying those pups for 22 months. Furthermore, all the pups would be relatively the same size.
But apparently that’s not the case at all with dogfish.
“Female spiny dogfish appear to be giving birth and producing pups year round,” said Sulikowski.
Fishermen who deal with dogfish on deck have long sensed this to be the case. Female dogfish have a high tendency to squeeze out pups no matter what time of year they’re caught.
But it usually takes documented science to change traditional mindset, and this latest work, which specifically looked at large females in their reproductive stages, is expected to advance the discussion.
The larger question, however, is: Does this reproductive phenomenon matter in the big picture?
Sulikowski thinks it does – and it might even explain why trawl survey data show the dogfish biomass increasing far faster than what is biologically feasible given the slow-growing nature of the species.
“I think we may be seeing the rebounding of the species much quicker because of this,” Sulikowski said.
Janice M. Plante
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