https://phys.org/news/2018-10-commercial-shellfish-decline-linked-environmental.html

The NAO is an irregular fluctuation of atmospheric pressure over the North Atlantic Ocean that impacts both weather and climate, especially in the winter and early spring in eastern North America and Europe. Shifts in the NAO affect the timing of species' reproduction, growth and availability of phytoplankton for food, and predator-prey relationships, all of which contribute to species abundance. The findings appear in Marine Fisheries Review.

"In the past, declines in bivalve mollusks have often been attributed to overfishing," said Clyde Mackenzie, a shellfish researcher at NOAA Fisheries' James J. Howard Marine Sciences Laboratory in Sandy Hook, NJ and lead author of the study. "We tried to understand the true causes of the decline, and after a lot of research and interviews with shellfishermen, shellfish constables, and others, we suggest that habitat degradation from a variety of environmental factors, not overfishing, is the primary reason."