ANCHORAGE - New imaging technology shows that Pacific herring rise to the surface of Prince William Sound at night to gulp down air.
Scientists say the discovery could be the missing link between the 1989 Exxon Valdez oil spill and the population crash of the once-plentiful fish. Herring are caught by commercial fishermen and eaten by larger fish and marine mammals.
The six-year study, led by Gary Thomas and Dick Thorne of the nonprofit Prince William Sound Science Center, was part of a $3 million federally funded project to assess the Sound's herring populations. Money came from the Prince William Sound Oil Spill Recovery Institute, created by Congress in 1990 to study long-range effects of the 11-million-gallon spill.
Researchers still have not established a direct connection between an unprecedented herring population crash in 1993, historic lows today and the spill. The studies reopen the question of what, if any, connection exists.
Until now, scientists have argued that herring stayed underwater, out of reach of the oil at the surface. The new study suggests that herring could have come into direct contact with crude.
"There's a new mechanism for potentially very, very high exposure to oil," Thomas said. "Whether we can actually go back and prove something that happened 10 years ago, I have some doubts on. We may never come up with absolute proof."
The center's researchers used sonar observations to prove something they have suspected since 1990: Beginning at dusk, schools of herring rise from as deep as 300 feet, surfacing to gulp air.
The spill oiled a significant portion of the intertidal and underwater grounds where herring spawn. Up to 6 inches of oil also covered the surface of the Sound.
Research by the Exxon Valdez Oil Spill Trustee Council - formed to oversee restoration with Exxon's $900 million civil settlement - showed that most of the oil dissipated by 1991. Studies underway last summer found, however, oil still lingers on hundreds of beaches.
Herring populations in the Sound crashed in the 1970s and built back up to a peak year in 1989. The herring population took a nose dive in 1993, recovered in the mid-1990s, peaked in 1997, then dropped again to about 5 percent of pre-spill levels.
The state has not allowed a commercial herring fishery since 1999 because spawning populations are at historic lows, said Steve Moffitt, an Alaska Department of Fish and Game biologist.
Today, fishermen continue to point fingers at the 1989 spill.
"Herring are the base of the food chain. If it hammered the herring, it ripples out to everything else," John Renner, a longtime Cordova fisherman, told the Anchorage Daily News. "The effects, I don't even like to think about it."
But the latest findings haven't swayed scientists.
The likelihood that the oil played a role in the herring crash is "very unlikely," said Gary Marty, a fish pathologist at the University of California at Davis studying the effect of disease on herring in the Sound.
Researchers found hydrocarbons in herring tissues in 1989; by 1990 the chemicals had returned to levels found naturally, Marty said.