In the Mid-Atlantic Bight—the coastal and estuarine waters from Cape Cod, Massachusetts, to Cape Hatteras, North Carolina—water temperature is increasing at twice the global rate. In the Chesapeake Bay, we are seeing shifts in where some fish species spend time due to climate change. The timing of when some species migrate in and out of the Bay has also been changing.
Changes in which species spend time in the Bay—and when—can affect how the entire food web works. So we need to understand what will happen not to just one species, but to the entire Chesapeake ecosystem. To learn more, the NOAA Chesapeake Bay Office funded research to help scientists explore these topics.
More Structured Habitat, More Summer Flounder and Black Sea Bass?
Researchers at the Virginia Institute of Marine Science wanted to learn more about how different habitats support juvenile summer flounder and black sea bass. Scientists wondered whether the amount of nursery habitat available in the Chesapeake Bay, as well as in oceanside lagoons on Virginia’s Eastern Shore, might affect how many juvenile fish there were in the Chesapeake Bay.
The scientists conducted field research in Virginia’s Piankatank River, which flows into the Chesapeake Bay, and in South Bay, a lagoon on Virginia’s Eastern Shore. They collected data on fish in seagrass areas, oyster reefs (or on-bottom oyster aquaculture), intertidal marshes, and unstructured soft bottom areas in both locations. They then compared the data from the Piankatank River to data from South Bay.
The South Bay location had more areas of structured habitats, especially seagrass. It was also closer to the open ocean, and had slightly saltier water. It also had more fish. Notably, South Bay had about 10 times more juvenile black sea bass than did the Piankatank.
In both locations, there were more juvenile fish in the marsh areas than in the other areas. This finding highlights the importance of marsh habitats as a nursery area for many species of fish. The Chesapeake Bay region has lost a lot of marsh area due to sea level rise. In some areas, marshes have “retreated” upland to compensate for those losses. But rates of sea level rise are accelerating. Unless marshes can migrate at a rate that keeps pace with rising seas, there will be less marsh area. And we don’t know whether newly formed marshes provide the same quality of habitat as do well-established marshes.
Researchers also noted that temperatures above 78.6°F hindered the growth of juvenile summer flounder. The area of the Chesapeake where bottom temperatures were less than 78.6°F has declined around 50 percent since 1996. Temperatures were most likely to become too hot for juvenile summer flounder in August. Summer flounder generally leave the Bay in late summer. But high temperatures in August could convince summer flounder to leave the Bay earlier than they traditionally have. This could explain declining catches of juvenile summer flounder observed in September, October, and November in recent years.
Are Fish Altering Their Geographic Ranges?
Another group of scientists at the Virginia Institute of Marine Science investigated how fish movements around the Mid-Atlantic Bight are changing in response to climate change. Different species of fish thrive in different water temperatures, and they seek out areas that have the right temperatures for them. As waters warm due to climate change, fish are moving north or offshore into deeper, cooler waters.
The researchers identified the temperatures preferred by Atlantic croaker, spot, summer flounder, and weakfish. This helps scientists anticipate how the distribution and habitat use of these species in the Chesapeake Bay will likely change with warming temperatures. The researchers expect the Chesapeake Bay will be used less by many species. Important fisheries species will instead inhabit cooler waters off the coast or more northerly estuaries like Delaware Bay. Some species are already using the Chesapeake Bay less.
Some species are less tolerant of low-oxygen water. Moving to stay in oxygen-rich water is critical for them. The research also emphasized the role that low-oxygen waters may play in delineating the areas of the Chesapeake Bay these fish can live in. As the climate changes, water column habitat will see other effects, including:
- Changes in salinity due to changing precipitation patterns
- Sea level rise
- Increased storm frequency and intensity
- Increased acidity
All of these changes may be felt more in shallower near-coastal and estuarine areas.
Where Do Black Sea Bass Like to Live?
Experts at the Coonamessett Farm Foundation, Inc., took a deeper dive into black sea bass movement patterns. They wanted to learn more about how they use inshore and offshore habitat. Black sea bass generally move closer to shore and into the Bay in spring and summer, and then return to offshore areas in fall and winter. But researchers wanted to learn more about how these fish use different areas of the Bay, and when—and why—they come and go.
Scientists used rod-and-reel surveys and tagged fish to learn more about their movements. They also analyzed where and when the fish spent time relative to water temperature and other water conditions. This information helped them investigate whether water conditions cued the fish to migrate and/or use different habitat areas and types. The researchers concluded that the typical movements of black sea bass throughout the year may be changing due to warming waters.
Researchers found larger black sea bass offshore and smaller ones closer to the mouth of the Chesapeake Bay. They also found them near the structures that make up the Chesapeake Bay Bridge-Tunnel near Norfolk, Virginia. The scientists deployed acoustic telemetry receivers to track tagged fish up the Bay near Annapolis, Maryland near the Bay Bridge. But they did not get any “hits” there. This may mean that the tagged black sea bass preferred to stay near structure-rich habitat near the mouth of the Bay or other offshore areas rather than to move so far up the Chesapeake.
Experts also tried something new: They fitted four black sea bass with tags that transmitted data via satellite. It was the first time black sea bass had been fitted with satellite tags. One satellite-tagged fish spent time in water colder than 50°F—that’s colder water than scientists previously had thought they would tolerate. It is difficult to attach satellite tags to smaller fish, and satellite tags are expensive. But as tag size gets smaller, there may be more opportunities to use them on different sizes and ages of black sea bass.
Findings from this research give scientists and resource managers more information, which helps them make decisions and set policies. The information can also help experts decide where and how to restore and protect habitat in the Chesapeake Bay to benefit fish.
The NOAA Chesapeake Bay Office plans to fund more research on how climate change may affect fisheries. A Notice of Funding Opportunity, which invites proposals for research on this topic, is currently open. Proposals are due by April 17, 2023.