LASERS GAUGE GROWTH OF FISH.

Byline: Judie Telfer Monterey County Herald

Twin red laser beams dance across the ocean floor, coming to rest as two dots, 50 millimeters apart, on a fish.

The new laser technology is allowing scientists to measure fish without catching or even touching them, in a study of adult rockfish in the Big Creek Marine Ecological Reserve.

Measuring the fish is an important step in determining whether the reserve, 50 miles south of Monterey, can help repopulate other areas where rockfish are becoming scarce because of overfishing.

``This is a pristine area,'' said David VenTresca, an associate marine biologist for the Resources Agency of the state Department of Fish and Game. ``Few people come down here to fish it.''

VenTresca is one of several scientists studying the two-square-mile reserve and he uses the new laser technology to do it.

The Big Creek reserve was set aside for research in 1994 as the result of Proposition 132, the initiative passed by voters in 1990 which prohibits fishermen from using gill nets.

John Smiley, manager of the Landels-Hill Big Creek Reserve owned by the University of California, Santa Cruz, said not only is fishing not allowed in the Big Creek reserve, but kayaking, recreational scuba diving and swimming also are outlawed.

``You're not allowed to be in it except for research purposes,'' Smiley said.

While he kayaks out to chase intruders, VenTresca and other researchers dive beneath the surface to count and measure the rockfish. The varieties they study are known as vermilion, copper, gopher, black-and-yellow, kelp, black, olive and china rockfish, as well as ling cod, cabezon and kelp greenling.

The state Department of Fish and Game estimates 95 percent of all fish caught on party boats from Monterey and Santa Cruz harbors in 1994 were species of rockfish, for a total of about 455,725 fish.

While sport fishermen prefer to catch salmon when available, party-boat owners consider rockfish their bread and butter.

Rockfish are live-bearers, VenTresca said, and an adult female releases an estimated 1 million larvae each December. The larvae travel at the whim of the currents for four or five months before the juvenile fish settle near the bottom in a kelp forest, where they stay for the rest of their long lives.

Rockfish off California can live for up to 60 years, though one species off Alaska has been known to live 100 years.

To show the value of the reserve, he said, ``we have to be able to show that the eggs and larvae go somewhere and enhance a fishery somewhere else.''

Evidence of that was found in 1988, when hundreds of two-inch-long vermilion rockfish were found along Cannery Row, where no adult fish of that species have been seen in recent years.

``That was a good year,'' VenTresca said. ``Those larvae had to come from somewhere else.''

It is impossible to track the tiny larvae to learn where they end up, so all that can be done is to measure and count the adult fish to see if the protection of the reserve means bigger fish or more fish within the reserve than in adjacent, nonprotected areas.

Before the new laser system was developed, VenTresca said, divers simply looked at a fish and counted it as an adult or sub-adult.

But to get the precise measurement the system is capable of, a diver takes a video image of the fish while sending out twin laser beams from the top of the waterproof housing.

At the Department of Fish and Game office in Monterey, researchers study the video, freezing the frame when they find a good, full-length side view of a fish with the laser tracks trained on it.

Using specially developed software, they tell the computer the distance between the two red dots is 50 millimeters and that they want to measure the fish from nose to tail. The computer does the rest.

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Photo

Photo: Twin lasers are trained on a rockfish to measure its length at the Big Creek Marine Ecological Reserve, south of Monterey.

Associated Press