In trying to untangle a herring crash from the aftermath of the 1989 Exxon Valdez oil spill, scientists in Prince William Sound are revealing just how resilient – and unpredictable – marine ecosystems can be.
October 13, 2017 — ON A COLD day in June, Scott Pegau leans toward the passenger window of a Cessna floatplane and peers out at the teal waters of Prince William Sound. The glacier-rimmed pocket of seawater on the southern coast of Alaska is protected from the open ocean by a string of rugged islands. It is both moody and alluring. Clouds dally on the snowy peaks and fray against the forested hillsides. The sea is flat and frigid, except for a single row of waves lapping at the rocky shore.
Pegau aims his gaze at the shallow waters behind the breakers. After a few minutes of searching, above a deep bay on one of the outer islands, he finally spots what he’s looking for: a school of juvenile herring. Pegau can distinguish them from other schooling species by the unique way they sparkle – an effect produced by sunlight playing off their silver flanks as the fish bank and roll. Try as I might, I can’t make out any twinkling, just the inky splotch of a few tons of small fish swarming below the surface.
“Small H1,” Pegau says into the headset microphone, tucked snugly under his thick, gray mustache. That’s code for a small school of one-year-old herring. He enters the location on his computer; huddled in the back seat, I make a tick mark on the backup tally. It’s the first of dozens of schools we’ll see on our flight.
Pegau conducts these surveys every year in hopes of understanding what’s in store for the herring population in Prince William Sound. The fish mature and begin to join the spawning stock at the age of three, so the counts give scientists and managers a clue about how many adults may be coming up the pipeline. Researchers and fishers alike always hope the answer will be many. But every year for the past quarter century, they have been disappointed.
The herring population in Prince William Sound crashed in 1993, just four years after the Exxon Valdez oil spill released 11 million gallons of crude into these waters. The collapse put an end to an $8-million-dollar-a-year fishery, and left a hole in the middle of the marine food web. Scientists have spent years trying to understand if and how the spill played a role in the herring’s demise here, and the results have been hotly contested. All of the legal proceedings finally closed in 2015, with herring listed as an impacted species but with most herring fishers feeling poorly compensated.
Even more concerning is the fact that, unlike most species hit by the spill, the herring haven’t bounced back over the decades since. Populations of forage fish are known to boom and bust, so most scientists thought it was only a matter of time before they rebounded. But 25 years later, there’s still no sign of recovery on the horizon.
“There’s definitely a possibility that the ecosystem went through a tipping point,” says Pegau, who coordinates the herring program at the Prince William Sound Science Center, an independent research institute whose work is funded in part by money from the spill settlement. A host of factors, which scientists are still trying to untangle, could be to blame, from hungry whales to virulent disease. “There’s no one thing that’s keeping them down,” Pegau says. “I think pretty much everyone is convinced of that.”