BAR HARBOR — Maine’s shrimp fishery has been closed for nearly a decade after the stock’s collapse in 2013. Scientists are now saying a species of squid that came in with a historic ocean heatwave the year before may have been a “major player” in the shrimp’s downturn.
In 2012, the Gulf of Maine experienced some of the warmest ocean temperatures for the region in decades. Within a couple years, the cold-water-loving northern shrimp had a rapid decline and the fishery, a small but valued source of income for fishermen in the offseason, closed.
Anne Richards, a biologist at the Northeast Fisheries Science Center in Woods Hole, and Margaret Hunter, a biologist with the Maine Department of Marine Resources, studied the collapse and found that it coincided with a fluctuation of longfin squid, a major shrimp predator.
The squid is a “voracious and opportunistic” predator that Richards and Hunter believe expanded its distribution in the gulf during the heatwave and unexpectedly overlapped with the shrimp population’s movements to devastating results.
“It certainly could explain why shrimp declined so rapidly,” said Hunter last week.
Shrimp were under duress heading into 2012. The survival of baby shrimp depends on a large number of shrimp reproducing and cold ocean temperatures. In 2012, the waters in the region were two degrees Celsius above the 1982 to 2011 average and remained above average in all months of the year.
But those warm temperatures don’t seem to be enough to cause the collapse of the fishery in one year, Richards and Hunter reasoned. They looked at data from commercial fishing, ecosystem monitoring and surveys in the Gulf of Maine and found that the shrimp hadn’t simply moved to other parts of the gulf nor did commercial fishing wipe them out.
Of 11 predator species that had a population peak in one or more seasons in 2012, longfin squid were the only ones that clearly increased, and increased in the areas where shrimp are present. The early onset of spring in the gulf that year also meant that female shrimp were still inshore at a time when they normally would have left in cooler years. This change in patterns allowed for a rare overlap with when the longfin squid arrived and increased the chances for the squid to feed on the shrimp.
“They haven’t overlapped a great deal until that year,” said Hunter.
The biologists don’t have an exact idea on how large the increase of longfin squid was, nor do they have evidence from the stomachs of squid to make the hypothesis ironclad.
“It’s a theory,” Hunter said. “We can’t ever really prove it.”
The shrimp population has never really recovered, and researchers are still trying to figure out what factors are blocking the rebound of the species.
“That’s a big mystery,” Hunter said. “We’re pretty sure it has to do with temperature.”
But the finding does highlight that climate change is much more complicated than water temperatures rising. It is causing food webs to shift and creates new interactions between species that can be catastrophic, the researchers wrote in the study.
“It just highlights how unpredictable the effects of climate change may be,” Hunter said.
The current moratorium on shrimping is scheduled to end this year. Fishery regulators are expected to decide whether to continue it this winter.
Shrimpers have urged officials to open the fishery back up again to see what’s out there. If there aren’t enough shrimp, they won’t bother with the effort of rigging up and going out.
James West, a fisherman from Sorrento, went shrimping for years until the fishery closed. He didn’t remember catching any squid back then but hoped that regulators would let him go fishing again, even if it was on a super limited basis.
“I still think there are shrimp out there,” he said.
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