Researchers studying the decline of commercial shellfish landings between 1980 and 2010 have found that the decline is likely linked to environmental factors, not overfishing.
Warming ocean temperatures associated with a positive shift in the North Atlantic Oscillation (NAO), which led to habitat degradation including increased predation, are the key reasons for the decline of eastern oysters, northern quahogs, softshell clams and northern bay scallops in estuaries and bays from Maine to North Carolina, according to findings which appear in Marine Fisheries Review.
“In the past, declines in bivalve mollusks have often been attributed to overfishing,” said Clyde Mackenzie, 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.”
Pressure fluctuation
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.
Exceptions to these declines have been a sharp increase in the landings of northern quahogs in Connecticut and American lobsters in Maine.
