Forage fish key to food chain
Date: November 3,1999
FAIRBANKS, Alaska -- Natives, fishermen, and scientists have long believed Prince William Sound is an important feeding zone for commercially caught fish, seabirds and marine mammals. Now, researchers have the photographs and videotape to prove it.
University of Alaska Fairbanks scientists today released aerial and underwater photographs taken during a three-year study to better understand the importance of herring, sand lance and other forage fish to the sound's ecosystem.
"Many of the photos are interesting from a scientific perspective, but also the general public will like them too," said Evelyn Brown, the study's lead scientist and research associate at the UAF School of Fisheries and Ocean Sciences.
The photographs show shimmering schools of juvenile herring and sand lance being attacked by auklets, kittiwakes and other diving seabirds. One image shows a large salmon, mouth agape, plowing through a school of young herring. Aerial video footage shows humpback whales, sea lions, and seals feeding on forage fish.
"Forage fish are the underdogs out there, everything eats them," said Brown. "But we've never been able to observe firsthand just how salmon prey on herring, or how herring react to diving seabirds. These photos give us a perspective we've never had before."
Researchers used a spotter planed equipped with a digital camera to photograph forage fish at the surface. Down on the water researchers aboard the Cordova-based fishing vessel Lucky, equipped with an underwater camera mounted on an aluminum pole, would idle up to the school.
"If the fish school was feeding, we could see that they spread out a bit," said Brown. "But when they were being chased by salmon or dived on by seabirds, the school got more compact."
The images also revealed new information about how diving seabirds inadvertently helped non-diving seabirds.
"When the schools are being fed on by diving birds--the kittiwakes and the auklets--they drive the herring up to the surface where the gulls and the other birds that can't dive are able to get them. They kind of work together," said Brown.
All this activity is triggered each spring as tiny crustaceans, called zooplankton, bloom near the water's surface. Schools of forage fish, sometimes thousands of tons each, swarm to the surface where they are easily spotted from the air. Large, nearly perfect circles that shimmer in the sun are likely to be schools of herring, while irregular-shaped schools close to shore are likely to be sand lance.
And while she can't prove it, Brown says seabirds seem to recognize the school shapes and usually target the best fish--the herring.
"It appears that even though the sand lance are there in the hundreds--probably thousands--of tons, the seabirds still seem to prefer the herring," said Brown. "We think it's a nutritional thing. The sand lance in the sound are young of the year and don't have as much fat as herring. So the quality of feed, from the seabird's perspective, is important."
"There is something special about these spots," said Brown. "You'd want to know, for example, where these nursery sites are if there was ever another oil spill. Before this study we really didn't know where these areas were or anything about these juvenile fish."
Brown's study was a continuation of studies begun following dramatic declines in herring numbers in Prince William Sound after the 1989 Exxon Valdez oil spill. Support for the study was provided by the Exxon Valdez Oil Spill Trustee Council.
This study would not have been possible without the help of the following: Tim Veenstra, private pilot and spotter, and Cordova Air Service; Stephanie Mooreland, UAF/SFOS; ADF&G; Torie Baker, Cordova fisherman; other Cordova area commercial and sport charter fishermen.
The Alaska Sea Grant College Program is a marine research, education and outreach service headquartered at the University of Alaska Fairbanks, School of Fisheries and Ocean Sciences. Sea Grant is funded by the National Oceanic and Atmospheric Administration in partnership with the State of Alaska and private industry.
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