Oyster losses are not due to climate change alone

A recent article in The Baltimore Sun (“Research links dramatic declines in Chesapeake Bay oyster population to warmer winters — not overfishing,” Oct. 30) described a study concluding that a climate cycle, rather than overharvest and habitat degradation, was the primary cause of the decline of oysters along the East Coast. Unfortunately, the study reflected a selective assessment of the scientific evidence, rendering its conclusion unfounded.

The study focused on a climate cycle — the North Atlantic Oscillation (NAO). The NAO influences temperature and precipitation on the Atlantic coast, which the study attempted to link to disease outbreaks, poor reproduction and increased predation. However, it neglected to discuss the voluminous scientific evidence demonstrating that overharvesting and destruction of oyster reefs over the past 150 years caused the collapse of oyster populations.

Overfishing’s role in the decline of oyster populations is well documented. A 2004 study by the Scripps Institution of Oceanography tracked the collapse of oyster fisheries along the East Coast. Oyster stocks were depleted sequentially from New England through the southeast as fishermen moved to more fertile southern grounds, such as the Chesapeake Bay, after stocks had collapsed in northern locations.

A 2011 University of Maryland Center for Environmental Science study showed that oyster populations in Chesapeake Bay declined by more than 99 percent from the 1880s to 1980. This study also concluded that further declines from 1980 to 2009, when diseases and poor water quality were also threatening oyster populations, were driven by overfishing and habitat loss.

Finally, researchers at the Virginia Institute of Marine Science have convincingly demonstrated that properly constructed oyster reefs protected from fishing persist indefinitely, even whenstressed by environmental factors.

We do not deny that disease, poor water quality, and other factors can negatively impact oysters, but major oyster declines occurred well before the onset of diseases and “dead zones” that now plague many ecosystems. The authors’ contention that warm climate periods cause oyster collapses also fails to acknowledge thriving oyster populations in the southeastern U.S. and Gulf of Mexico where waters are much warmer than in the northeast.

To rebuild oyster populations, we must focus on rebuilding their resilience to environmental change by using all the tools available to us. That means improving water quality, investing in restoration, and properly managing oyster fisheries — not just to maximize harvest, but to help rebuild sanctuary reefs. We must strive for a trajectory toward oyster recovery in spite of environmental change, not resign ourselves to failure because of it.

Allison Colden, Romuald Lipcius and Tom Miller

The writers are, respectively, Maryland fisheries scientist with the Chesapeake Bay Foundation, professor of marine science for the Virginia Institute of Marine Science and Chesapeake Biological Laboratory director and professor of fisheries science for the University of Maryland Center for Environmental Science.