Project Evaluates Impactsby Barry Espenson
The can't exactly be described as Casper the Friendly Ghost nets, but commercial harvest gear inadvertently left adrift in the Columbia River reservoirs above Bonneville Dam do not appear to be doing much harm to migrating salmon.
A project to evaluate the damage being done by these so-called "ghosts nets," and to remove them from the river, was cited in a recent Federal Caucus mailing as one of the hundreds of steps that have been taken since late 2000 to improve the survival of salmon and steelhead stocks listed under the Endangered Species Act.
It appears that the lost gill nets can be crossed off the list of suspects that cause the "unaccounted loss" of adult salmon and steelhead as they swim upstream.
The project to find, mark and remove the nets was carried out in fiscal years 2001 ($65,000) and 2002 ($15,000) through the Columbia River Inter-Tribal Fish Commission.
Researchers used high resolution side-scan sonar to survey the river bottom in popular fishing areas in the Bonneville Dam pool. The mainstem pools above Bonneville are reserved for tribal commercial fishers, who each year lose some gear as a result of changing water conditions, river traffic and, on occasion, vandalism.
The researchers identified suspected lost nets, then dragged those areas using a 73-foot commercial trawling vessel and crew. Eight nets were recovered.
"They didn't find any salmon bones or carcasses" in the nets, said John Skidmore of the Bonneville Power Administration.
"White sturgeon were the only fish species recovered in the retrieved 'ghost nets'. A total of eight nets were recovered containing 80 carcasses and/or notochords of white sturgeon," according to a CRITFC summary of the effort. "Our findings indicate that the impact of lost nets on salmon species appears to be low to non existent, but the impact on white sturgeon may justify further programs to recover lost gillnets and/or reduce the occurrence of lost nets."
The project won funding in the summer of 2001 through BPA's so-called "action plan" -- a special fish project solicitation intended to mitigate from impacts from emergency hydrosystem operations employed because of a severe drought. Those operations included the curtailment of spill designed to ease dam passage for migrating salmon.
The feasibility study was launched because it was believed that the lost nets could be a substantial threat to salmon that could become entangled as they migrated upstream to spawn. Lost high seas drift nets had become notorious for causing fish mortality as they drifted unattended, and unfurled.
But the lost nets in the Columbia River's current seem to show a tendency to wrap around rocks, and/or ball up, instead of staying in a deployed position, Skidmore said.
"It was not the big impact that we thought," said Mike Matylewich, head of CRITFC's fisheries department. CRITFC's member tribes are the Yakima, Warm Springs, Umatilla and Nez Perce, who harvest salmon, steelhead, sturgeon and other fish species for ceremonial and subsistence, as well as commercial purposes.
Skidmore said further funding for the effort was contingent on the results. So with salmon impact undetected, BPA and NOAA Fisheries no longer find the effort fundable for ESA purposes. But the tribes would like to continue the net removal project.
"People tell us they're down there so we want to try again," Matylewich said. A crew will venture out again within the next few weeks, buoyed by funds from a non-profit foundation.
"Ocean Trust has given us a small amount of money to do some followup," Matylewich said. Ocean Trust is a member-supported, ocean conservation foundation directed by scientists, naturalists, chefs, musicians, and fisherman who share an interest in the ocean and human's dependence on its resources. The Virginia-based organization conducts research, education, and environmental enhancement projects on fishery, ocean wildlife and marine ecosystem issues.
The study was initially designed to 1) determine the presence and extent of lost gill nets and the threat they pose to aquatic species, 2) test the efficacy of locating lost nets using a side scan sonar, and 3) develop recovery methods and test the feasibility of recovering lost gill nets.
The sonor search was conducted in Bonneville Reservoir using a 19-foot Alumaweld with a center davit, and performed near shore transects using a SSS and a fish finder to image suspected targets, and a Global Positioning System (GPS) to run selected transects and mark suspected targets. The search was focused on sites known to be used by commercial fishermen.
Thirteen days were spent searching for and marking nets. The net recovery operations were successful but challenging, according to the CRITFC. Among those challenges were the Columbia River's high current velocity, shallow water hazards, variable substrates and dramatic and varying bottom topography including jagged basalt outcropping.
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