Scientists devise sonar
system to help save
bottom fish
By Helen Altonn
Star-Bulletin
A sonar system is being developed to detect and count Hawaii's valuable ehu and other endangered bottom-fish species.
The project is one of several research efforts at the University of Hawaii's Institute of Marine Biology at Coconut Island aimed at preserving the valuable snappers.
Whitlow Au, chief scientist in the Marine Mammal Research Program, and graduate student Kelly Benoit-Bird are working on the sonar system.
Benoit-Bird said they are building equipment for trials to look at individual animals in a floating enclosure in Kaneohe Bay.
"We're trying to look at different species of bottom fish, as well as species we might encounter that we're not really interested in."
She said they are using different frequencies and a broad-band signal -- "essentially the equipment the dolphin uses for eco-location, so we can figure out the best signal to use in the field."
Chris Kelley, a UH biologist who is studying bottom fish and their habitats in a state-funded program, said it is difficult to identify them in the deep ocean. "If there are many species on the bottom, they are blobs on the screen."
Sonar will reflect off fish in a different way, he said. So it may be possible to identify acoustic signatures for various species by bringing fish up alive from the bottom and exposing them to different signals, he explained.
A deep-water camera system also is being developed to use without artificial lighting on submersible dives, Kelley said.
By keeping the sub's lights off and using bait, they can attract fish to study them and get images, he said.
In another approach to improving the critical bottom-fish situation, Kelley is working with research associate Aaron Moriwake to raise species in hatchery conditions at Coconut Island.
"A clear target for release would be the reserves. Then we could try stocking other overfished areas," he said.
Some ehu spawnings occurred, and the researchers were able to document the early life stages of an ehu egg's development -- never seen before.
Kelley said they kept larvae alive five days last year and 11 days this year. "It's a big challenge keeping them alive."
Onaga were not happy in the tanks because they are bigger fish requiring bigger movements, he said. Thus, rearing efforts are focused on ehu and opakapaka.
The opakapaka had "popeye" problems in the hatchery -- bulging eyes because of a gas-bubble disease. But Kelley said a bunch of them were placed in net pens in Kaneohe Bay, and some are more than a year old with no signs of the disease.
The researchers now are trying ehu in shallow-water net pens, which has not been done before, he said.
HIMB scientists also are doing DNA analysis on bottom fish in the Northwestern Hawaiian Islands and the main islands.
They found no difference, so the Western Pacific Fisheries Management Council views the fish as a single stock, Kelley said.
Based on that, the council said the northwestern islands are not being overfished, he said.
Although there is localized stock depletion in the main islands, they are probably getting fish seed from the northwestern islands, he said.
