For months, scientists have debated — with little consensus — what is behind the apparent increase in the number of sick and seemingly malnourished striped bass in the Chesapeake Bay.
An effort to find defensible answers may soon be under way.
After meeting with scientists from government agencies and universities in September, Rep. Wayne Gilchrest, R-MD, said he planned to meet with the governors of Maryland and Virginia, as well as members of Congress, to push for a coordinated research program to examine the problem.
“I think pfiesteria set a pretty interesting precedent in that you had all these federal, state and local government people and agencies, along with university scientists, and they pulled together a really quick emergency response team to deal with pfiesteria,” Gilchrest said. “Now, pfiesteria is a pencil point compared to this other thing.”
While not everyone agrees with that, many scientists do say something appears seriously wrong with striped bass. But most say there is no conclusive evidence as to what factor — or combination of factors — is at the root of the problem.
Last fall, more than 10 percent of adult striped bass taken during Maryland Department of Natural Resources surveys had lesions. In Virginia, the percent may have been even higher in some places.
The number declined this spring but was on the rise again this summer. “It may be approaching 10 percent to 20 percent right now in the Potomac,” said Wolfgang Vogelbein, a fish pathologist with the Virginia Institute of Marine Science.
Robert Bachman, director of resource management in the DNR’s Fisheries Service, said late summer surveys were finding that about 10 percent of the striped bass had lesions or some kind of marks on them.
So far, Vogelbein has identified four types of bacteria belonging to the genus Mycobacterium, which appear to have caused the lesions. Mycobacterium may also infect humans if they are handled by someone with open cuts or abrasions on their hands, especially if they have a disease that compromises their immune systems.
What’s less clear is whether Mycobacterium is, for some reason, sweeping through the striped bass population on its own, or whether the fish are suffering from some other stress that make them more susceptible to this bacterial infection.
Possible stressors could include poor water quality, having too many fish crowded into restricted habitats, or other factors. A likely suspect, though, is that the fish are not getting enough to eat.
“There’s a lot of circumstantial evidence and anecdotal evidence on that question, but not anything we can hang our hats on,” said Steve Jordan, director of the Cooperative Oxford Laboratory, a joint DNR-National Marine Fisheries Service facility.
For example, menhaden — a major food for striped bass — are at low numbers in the Bay. Besides menhaden, other fish that striped bass eat, such as bay anchovies, appear to be in short supply. At the same time, the number of striped bass in the Bay, and the number of large striped bass — which require more food — is higher than it has been in decades.
Jordan and others say that many fish that have been examined are thin, with no evidence of food in their stomachs.
Some have also raised concern that the food menhaden eat, zooplankton, have undergone population shifts in the Bay, with less desirable species of the fish food becoming dominant in some areas.
The issues have been discussed for months among scientists, and the Bay Program’s Scientific and Technical Advisory Committee held a workshop on the issue this summer, but there was no clear consensus on what is going on.
But with suspicion running high that the problem relates to an imbalance between the striped bass and menhaden populations, some blame management agencies for failing to account for how management of one fish species affects another.
Because of such concerns, the Atlantic States Marine Fisheries Commission — a multistate panel responsible for managing migratory species — earlier this year called for a review of menhaden harvests to see whether there are enough fish to support both commercial fish catches, and supply food for predatory fish such as striped bass, weakfish and bluefish.
“We are not managing menhaden for anything other than maximizing that harvest,” said Bill Goldsborough, senior scientist with the Chesapeake Bay Foundation. “We are not incorporating the important ecological roles that menhaden play in the system.”
Not only are those interconnections not considered, he said, but management has been completely different for striped bass and menhaden. The emphasis for striped bass has been to reduce catches to allow the population to rebuild, while menhaden management has sought to maintain high commercial harvests.
“We are not applying the same level of conservatism across the board,” Goldsborough said. “We’ve been extremely conservative with striped bass. We haven’t been conservative at all with menhaden.”
Bolstering the notion of a striped bass-menhaden connection is that smaller striped bass appear to be afflicted this year, said Jim Price, president of the Chesapeake Bay Acid Rain Foundation. Small striped bass eat small menhaden, which are in particularly short supply because of several years of poor reproduction.
“It gets down to 12-inch fish that are starving,” hesaid. Last year, Price said he rarely saw the problem in fish less than 18 inches. Vogelbein, though, said he found the condition in both small and larger fish this year and last.
But convincing the ASMFC that either more striped bass should be harvested or fewer menhaden caught would require “compelling evidence,” Bachman said. Right now, he said, that evidence doesn’t exist. One problem in explaining the connection, he said, is that striped bass in some areas are healthier than those in others. And it may be that there is no connection between the lesions and the thin fish. “Just because something makes sense doesn’t necessarily mean that it is true.”
The proposed study, Jordan said, would allow scientists to gather more detailed information about the number of sick fish, what they are eating, where they are found, and whether different sizes of fish are disproportionately affected.
Laboratory tests may examine whether — and how — Mycobacterium is spread among fish, whether the infected fish die, or whether they recover.
Emaciation is also a symptom of Mycobacterium infections, so scientists say it is important to examine fish without sores to see if they have early stages .of Mycobacterium infections. In Virginia, Vogelbein has begun looking at these issues, but no results are yet available.