Herring deaths a mystery
Published 6:00 am Saturday, May 22, 2004
Researchers are puzzled by a high mortality rate among egg samples in a spawning ground at Hidden Cove.
Hidden Cove has a real whodunit – herring eggs laid there are dying.
Although signs point to a toxic compound as the cause, embryologists with the state Department of Fish and Wildlife haven’t seen this type of mortality before.
“(We’re) seeing cell death that isn’t consistent with the published literature,” said Jim West, a research scientist with Fish and Wildlife.
Studies show that herring egg mortality in Hidden Cove is unusually high and chronic, yet also unpredictable. While some data suggest toxic compounds from oil – polycyclic aromatic hydrocarbons, or PAHs – found in the water could be the cause, not all the evidence supports that conclusion, and more targeted research is needed, West says.
“Interpreting these mortality ‘estimates’ is tricky,” he said, “because the monitoring efforts that have provided the info are designed to estimate egg densities for herring abundance – not to monitor egg mortality.”
West came across the mystery while helping an oil spill response group measure the potential impact of future spills, by studying baseline conditions for herring and PAHs in Puget Sound.
A “forage fish” eaten by a wide variety of birds and other fish, Pacific herring is considered a “keystone species,” because its health reflects that of the larger ecosystem.
Unlike other fish species, herring are highly affected by human activity because they spawn in shallow waters at the shoreline. Eggs laid on red algae may be as little as a foot below the water at low tide.
A sweep of five spawning grounds by the Puget Sound Ambient Monitoring Program found high herring egg mortality at Hidden Cove on Bainbridge, as well as at Port Gamble on the Kitsap Peninsula and Quartermaster Harbor on Vashon-Maury Island.
The DFW’s forage fish unit, which has monitored herring since the late 1970s, has known about the mortality problem for the last 20 years. But tests conducted in 1985 by the state Department of Ecology, proved inconclusive, unable to link mortality rates to PAH toxins using the detection methods of the time.
Normal herring egg mortality is about 5 percent, but West found chronic mortality of 50 percent to 90 percent in Hidden Cove.
Water quality tests ruled out some causes, while PAH levels were highest at Hidden Cove of the five monitored spawning grounds.
Further tests showed that eggs were absorbing the toxins as they incubated, and that the toxins in shoreline sediment shared the same chemical profile, or “fingerprint,” as those in the eggs.
The puzzle is that the current literature describes embryo death from PAHs as simple degeneration of organs, not the cell death seen in the Hidden Cove eggs. Also, PAH concentrations in Hidden Cove’s “relatively clean sediment…aren’t very high,” West said.
From the viewpoint of maintaining a healthy number of herring in the Puget Sound ecosystem, Hidden Cove is not an immediate concern, since it is just one part of the herring stock that spawns from Port Madison to Fletcher Bay.
Also, the “fingerprint” of PAHs found in Hidden Cove point to their being a by-product of wood burning, rather than having spills as their source, and West theorizes that residual pollution from old sawmills may be the source.
Port Gamble and Quartermaster Harbor share an industrial history with Hidden Cove; in their heyday, sawmills burned tree waste intensely.
PAHs generated over a century ago could still remain. Alaska herring still show effects from the 1989 Exxon Valdez oil spill in Prince William Sound, because of oil gathering in their spawning grounds.
The mystery has piqued the interest of the Bainbridge Island Watershed Council, which is talking with the high school about a research project. New equipment arriving in the fall will enable students using the school’s electron microscope to examine organic matter.
West cautions that, while the mystery could make a good science project and would benefit from volunteer help, he has limited time and few resources to offer. PAH tests alone run upwards of $700.
“The next step is finding a link between mortality and a toxin, if that’s what is doing it,” West said. “Then, I could publish information, have it reviewed and hand it off to the proper agency.”
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The Bainbridge Island Watershed Council sponsors an informational talk by Jim West of the Washington State Department of Fish and Wildlife, about herring and the mystery of herring egg mortality in Hidden Cove at 7 p.m. May 27 at the Bainbridge High School Commons. Information: 780-1246.
