New Study Reveals Chesapeake Bay Dead Zone Hits Fish Hard

The dead zones that characterize Chesapeake Bay during the summer may be having a major impact on fish. A 10-year study has recently revealed that these low-oxygen areas are impacting the distribution and abundance of fish that live and feed near the Bay bottom, which could be a major issue for fisheries in the area.

Dead zones usually form when excessive loads of nitrogen from fertilizers, sewage and other sources are dumped into the water. These nutrients then "feed" algal blooms. While the algae produce oxygen when they're alive, though, they soon die off.  They then sink to the bottom, providing a rich food source for bacteria. Unfortunately, these bacteria take up dissolved oxygen from nearby waters and create a condition called hypoxia, which are extremely low-oxygen conditions.

In order to study how these conditions might affect fish, researchers examined the distribution and abundance of late juvenile and adult fish caught and released in trawl nets during 48 sampling trips. The largest quantitative assessment of its kind, it allowed researchers to understand exactly how these summer-time dead zones were affecting Chesapeake Bay fish.

"The drastic decline we saw in species richness, species diversity and catch rate under low-oxygen conditions is consistent with work from other systems," said Andrew Buchheister, a student at William & Mary's School of Marine Science at VIMS, in a news release. "It suggests that demersal fishes begin to avoid an area when levels of dissolved oxygen drop below about 4 milligrams per liter, as they start to suffer from physiological stress."

So which species were affected? Scientists found that Atlantic croaker, white perch, spot, striped bass and summer flounder were all greatly influenced by dead zones. All of these fish are key to the Chesapeake Bay ecosystem and support important commercial and recreational fisheries.

The study highlights the importance of monitoring how these hypoxic conditions can affect fish. In addition, it could help fisheries better manage the species that are being targeted.

"Continued monitoring will be critical for detecting how the Bay ecosystem responds to continued stresses from fishing, development and climate change," said Rob Latour, one of the researchers, in a news release. "It's an essential component to a successful management strategy for the marine resources of Chesapeake Bay and the coastal Atlantic.

The findings are published in the journal Marine Ecology Progress Series.