A Rash of Mysterious Fish Kills

By NRNS Correspondent Maggie Master

When large numbers of dead fish turned up in the nation’s waterways, the reason was usually obvious.

If 10 million silvery-backed menhaden were floating belly up on North Carolina’s Neuse River, it was a safe bet there had been a manure spill at one of the nearby hog farms.

When 30,000 fall Chinook salmon littered the shores of California’s Klamath River in 2002, the cause was obvious: not enough water in the riverbed after farmers diverted it for agriculture.

Historically, massive fish die-offs might have been disturbing, but they were generally not mysterious.

So when a rash of fish kills began leaving a wake of lesioned fish corpses but no smoking gun, scientists took notice. In the last four years, millions of fish have died in kills from Florida to Connecticut, with no obvious culprit besides their crippled immune systems.

This lack of a known cause has prompted a growing number of scientists to develop a new – and troubling– hypothesis: the die offs aren’t the result of any one pollutant or stressor; rather, they are the product of a “perfect storm” of multiple factors.

The consensus now developing is that the cumulative effect of these stressors is bringing streams, rivers and bays across the country to a tipping point beyond which there will be nothing humans can do to reverse the inevitable. The multitude of contributing factors and uncertainty over the relative importance of each already makes corrective action difficult to agree on.

National Public Radio's Elizabeth Shogren explored this issue for All Things Considered in a report that aired January 18, 2006. Her story features interviews with sources quoted here and can be downloaded at this link.

Taken individually, the factors plaguing U,S. waterways are old news. Urban and agricultural runoff, booming populations, and pharmaceuticals flushed down toilets have long placed stress on aquatic ecosystems. But a growing number of scientists believe that the combination of these factors – exacerbated by warmer water temperatures – is taxing fish populations, resulting in large numbers of deaths. Scientists point to more than a dozen states across the Eastern United States and parts of the Midwest that have experienced unexplained fish kills in the past three years as evidence of the multiple-stressors phenomenon.

“That [perfect storm] thought is out there on the table,” said Don Kain with the Virginia Department of Environmental Quality. The theory has weight, he notes, because scientists are unable to pinpoint any one cause for mass fish deaths such as the one that nearly decimated the small mouth bass population on Virginia’s Shenandoah River last spring.

An estimated 80 percent of the Shenandoah’s adult smallmouth bass and sunfish died last spring and summer. Most were covered in bacterial lesions, a hallmark of many recent kills. Considered a secondary effect, these sores arise because aquatic bacteria take advantage of a fish’s weakened immune system. The cause of this immune-suppression is what has left most scientists scratching their heads.

Steven Smith, a fish pathologist at Virginia Tech who participated in an investigation of the Shenandoah kill, predicts similar incidents will become more and more frequent. The Shenandoah provides fodder for such grim forecasts: it is the third in a string of unexplained smallmouth bass kills in that watershed in just four years. Bacterial lesions were also involved in a bass kill on the Potomac River in 2002 and the North Fork Shenandoah River in 2004.

“Too many times we’re looking for one answer,” Smith said, noting that scientists should be looking at all the factors at play in a river, including fishing, agricultural and industrial runoff, and warming temperatures.

Similar sentiments have been voiced by scientists and environmentalists in other watersheds, but part of the difficulty in understanding the problem may be a lack of interstate dialogue and information sharing. “The focus has been myopic,” said Chesapeake Bay Foundation scientist advocate Harry Campbell of kills such as last summer’s die-off of thousands of lesioned bass on the Susquehanna River in Pennsylvania. Information sharing would help determine whether these mass deaths are the “canary in the coalmine or just an anomaly,” Campbell says.

Vicki Blazer, a fish pathologist with the National Fish Health Laboratory in Leetown, WV, who studies the Shenandoah, agrees that the problem requires a big-picture, regional approach. “You get little pieces here and there,” Blazer said. “Let’s put something together where we’re looking at the Shenandoah, the Susquehanna and the Potomac, all of which dump into the Chesapeake.” Yet many state officials seem reluctant to do much information sharing, simply because there isn’t much information to offer. “We’re not ready to share an answer,” said Andy Shields of the Pennsylvania Fishing and Boating Commission. “We’re still trying to get our hands around what’s happening here.”

Even without solid answers, there may be a compelling reason for Eastern states to collaborate in their investigations: the Chesapeake Bay. The bay has been no stranger to environmental woes, most significantly agricultural runoff from area poultry farms. But recently, bay-area scientists have begun to suspect a possible connection between die-offs in the bay’s tributaries and a rapidly spreading sickness among the bay’s rockfish. Mycobacteria, a slow-wasting disease known as “fish tuberculosis,” now plagues as many as 80 percent of striped bass, the bay’s famed and most lucrative catch.

Almost three-quarters of resident rockfish have the disease internally, according to Virginia Institute of Marine Sciences’ Wolfgang Vogelbein, a rate of infection that has nearly tripled in seven years. Many of the fish have outward lesions and fishermen have complained of the declining quality and size of Bay rockfish. Vogelbein fears the disease is chronic and not receiving adequate attention.

Vogelbein, who noted that the mortality rate of rockfish has dramatically increased within that time frame, said the bay epidemic is a clear example of multiple stressors. He fears the worst is yet to come. “We are very concerned about this disease and the future of the striped bass in Chesapeake Bay,” he said. “We believe that the striped bass reflects a broader problem and that it may serve as a model for other types of fish kills and disease outbreaks in regions throughout the country.” Virginia Tech’s Smith said one reason the mid-Eastern United States has experienced the brunt of fish kills is because the region has the greatest fluctuation in water temperature ranges. As warming temperatures become a reality elsewhere, regions in the Northern and Southeastern United States, as well as the Great Lakes, will likely follow the fish kill trend, Smith said.

Most fish have an “ideal” temperature and rapid changes in that temperature can spell disaster, according to Cornell University fish pathologist Paul Bowser. There are many potentially harmful organisms waiting to prey on fish that are weakened or stressed, according to Bowser. And when water temperature spikes 10 degrees in a matter of days, that is just what happens. When a section of a river becomes “hypoxic” there is not enough oxygen in the water to support fish. The Chesapeake Bay has long been notorious for such “dead zones,” but Bowser and others are now trying to discern whether other stressors make fish more likely to succumb to hypoxia.

How warming patterns relate to fish kills is an issue scientists are beginning to monitor, including Stony Brook University professor, Alistair Dove. According to Dove, changes in the Long Island Sound’s water temperatures have been the driving force behind a decade-long lobster die off, with low oxygen levels and pollution exacerbating the situation. “There is very little doubt in my mind [kills] will increase in number and severity,” Dove said.

If indeed a host of bad actors are having a synergistic and deadly effect on fish, the implications are far more daunting than a spike in fish kills: Scientists are only beginning to understand the effects of individual stressors on aquatic life. The idea of discerning what magic combination of varying levels of hormones, nutrients, bacteria and changing water temperatures will result in a fish kill would be practically impossible.

In the meantime, the funding required to monitor fish kills is drying up. Blazer, whose team has also been studying the Mycobacteria epidemic in the Chesapeake, said it is unlikely the team will be funded for the project next year, due to competing interests and priorities in the bay. Dick Harris, director of Connecticut’s Harbor Watch Program for the Norwalk River, said the state’s fisheries department used to monitor the river—which experienced a major fish kill last fall—but no longer. The reason is dollars and cents, according to Harris: “Budget cuts. Budget cuts. Budget cuts.”

Ernie Pizzuto, a water quality supervisor for the Connecticut Department of Environmental Protection agrees that in most states, the water monitoring budgets are “pitiful.” Pizzuto has a staff of six to monitor water quality for the entire state, which includes bathing beaches as well as 5,800 miles of streams – or the length of the Canadian/U.S. and Mexican/U.S. border combined. Pizzuto likened the process to “continuously chasing your tail.” Virginia, at least, appears to be learning a lesson from recent kills. Don Kain of the Virginia Department of Environmental Quality said the state environmental agency plans extensive water quality monitoring for next spring, including detection of short-term water quality changes and daily water temperature monitoring. But with an ecosystem that is constantly in motion, Kain noted: “You can’t totally recreate the crime scene.”

Look out for Maggie Master's next story which will explore the perfect storm unfolding in the Chesapeake Bay, where a majority of the bay's Rockfish have contracted "fish tuberculosis" thanks to weakened, over-stressed immune systems.


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