The Chesapeake Bay and its watershed seem to be tough places to be a fish.
- The majority of adult striped bass in the Bay are infected with mycobacteriosis, a chronic wasting disease.
- Many menhaden in low-salinity areas are afflicted with ulcerative lesions caused by the fungal pathogen, Aphanomyces invadans, which may be lethal.
- Cancerous tumors have been found in brown bullhead catfish and mummichog. While the cancers have been found primarily in highly contaminated areas, such as the Elizabeth and Anacostia rivers, some have also turned up in the South River, an area not associated with particularly high contaminant levels.
- Unexplained fish kills have plagued parts of the Potomac drainage since 2002, primarily in the Shenandoah watershed. During some events, as many as 80 percent of the adult smallmouth bass and redbreast sunfish have died.
- A high prevalence of intersex (the presence of eggs inside male testes) has turned up in male fish of some species in the Potomac watershed.
- Skin lesions and large numbers of dead smallmouth bass were reported in the Susquehanna and Juniata Rivers in Pennsylvania in 2005, apparently associated with the bacterial agent Flavobacterium columnare.
“When you look at them altogether, I think it does sort of hit you that things aren’t right with the system,” said Beth McGee, senior regional water quality scientist with the Chesapeake Bay Foundation.
What’s less clear is exactly what’s not right with Bay and at least some of its tributaries. In January, scientists, agency representatives, environmentalists and others gathered for a workshop to explore whether any common thread links the myriad fish health issues that have arisen in the Bay region and recommend future research and actions.
The fragments of available information did not lend themselves to solid conclusions. In fact, it’s not even entirely certain whether fish health problems are becoming more widespread—or they are just grabbing more attention. Indeed, many large kills were reported in past decades.
“There certainly is a perception among many of us that things are getting worse, but I don’t know if it’s true,” said Wolfgang Vogelbein, a fish pathologist at the Virginia Institute of Marine Science. “We certainly have been looking harder in the last 10 or so years.”
But there was a strong sense at the workshop that the way in which fish kills take place seems to be changing. In the past, large kills were often linked to a specific discharge, spill or disease. Many of the recent problems have been more chronic, and don’t seem to be related to a single pollutant or problem.
Fish kills in the Shenandoah affecting multiple species of fish have taken place at various places of both the North and South forks, and at different times of the year. “The fish aren’t dying in one instance,” McGee said.
In the Shenandoah, fish in some cases have shown high levels of external lesions and/or internal parasites and bacteria. As a rule of thumb, biologists say fish are more susceptible to infections when they are stressed—which compromises their immune systems—but it’s unclear exactly what those stresses may be.
“The underlying environmental degradation is perhaps a commonality in all of these things,” Vogelbein said, “That is why we think these are indicators of sorts for reduced habitat and water quality.”
Increased nutrients, for instance, contribute to low oxygen levels in both the Bay and freshwater tributaries. Blooms of harmful algae, such as the toxin- producing Karlodinium, which has caused several large fish kills in the Bay, may increase with high nutrient levels. It’s possible that concentrations of some harmful primitive photosynthetic cells, such as cyanobacteria (formerly known as blue-green algae) may be on the rise in freshwater areas.
In the Shenandoah, monitoring observed large daily fluctuations of pH and ammonia during the time of some fish kills—something that can be influenced by large amounts of algae in the water.
Another stress may be rising water temperatures in the region. The Bay’s temperature has increased about 2 degrees in recent years, and some scientists say that the Shenandoah’s has increased about 5 degrees.
That can be a problem for many fish species, from striped bass in the Chesapeake to smallmouth bass in the Shenandoah. Warmer temperatures also increase the oxygen demand for fish and may create conditions conducive to the growth of pathogens.
“I do think we are moving toward environmental conditions that allow for a greater expression of pathogens, at least theoretically, than they would be in the past at lower water temperatures,” said Kevin Sellner, executive director of the Chesapeake Research Consortium, which includes the major research institutions around the Bay.
Added in the mix of traditional chemical pollutants are hormone-altering endocrine disrupters—considered a likely cause of intersex fish in the Potomac—which can come from many sources, including pharmaceuticals in human waste discharges from sewage plants; herbicides and pesticides used in agriculture; natural and synthetic hormones from animal waste; and as byproducts from many chemicals.
“We may be overwhelming the fishes’ capacity to respond as the environment gets warmer,” Sellner said.
But, water quality is not necessarily the root of all fish ills in the system. Many, for instance, believe striped bass are stressed by the low abundance of menhaden in the Bay, which are considered a major food source.
Nonetheless, workshop participants agreed that stepped-up efforts to curb water pollution from farms, urban areas and other sources could reduce stress on fish.
“It is just one more reason why we need to be upgrading our sewage treatment plants and controlling runoff from suburban and agricultural lands,” McGee said. “It’s not just about the dead zone in the Bay.”
Recommendations from the workshop also called for the stepped-up monitoring of contaminants in areas of the watershed that have gone largely unmonitored in the past.
They also called for standardized protocols across the region for collecting samples and responding to fish kills. The lack of water samples taken at the time of kills, and even “fresh” fish from kills has sometimes hampered efforts to find causes.
Another recommendation was that the Bay Program include measures of fish health to help provide a more complete picture of ecosystem health. Right now, for instance, some indicators show that striped bass populations are at high levels without also mentioning the high rate of disease within the population.