OVER-THE-COUNTER LASERS PROVE USEFUL AS NEW FISH MONITORING DEVICE

Over the past eight days, aquatic biologist Bill Walsh and his team of fish trackers have been diving the reefs and lagoons of the Northwestern Hawaiian Islands as part of a month-long expedition to learn more about the underwater inhabitants of these remote islands and atolls. To do their work, Walsh and team are experimenting with a new, yet relatively simple technology to study reef fish -- underwater laser lights.

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These lasers are enabling these scientists to gather more accurate information about the size and calculated biomass of fish found in the northwestern chain.

These lasers are much like the hand-held laser pointers used in boardrooms around the world that can be purchased over-the-counter at office supply stores. How they differ is that they have waterproof housings that enables their use underwater, are more powerful, and the light emitted by them is green, not red.

The way these lasers work is that two of them are mounted (a known distance apart) on video cameras that are recording the fish being sized and counted. The lasers project beams of light that create two dots on the fish which, from any distance, measure exactly 10 centimeters. After their dives, the scientists review the video images taken of the fish and are able to accurately assess the fish's length.

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According to Walsh, these relatively inexpensive lasers are already proving to be very useful to science. "These lasers enable us to get an accurate measurement of fish we see underwater. In establishing baseline information about fish found at the remote reefs of the Northwestern Hawaiian Islands, having accurate information is paramount.

"One of the main things we are looking at are differences in size of fishes between the main and Northwestern Hawaiian Islands," said Walsh. "For example we would like to compare the sizes of species like ulua, omilu, uhu, weke, fishes that have been commercially and heavily exploited in the main Hawaiian Islands for many years. With more accurate sizing techniques, we can more accurately calculate the size and quantity of various fish species and what impacts like fishing are doing to their populations."

When fish are counted and sized, scientists use a conversion factor (using the to determine the weight of fish) to calculate the biomass, or total weight of fish, found at a particular place. This information enables the scientists to compare the difference in fish abundance between populations of species found in the main and Northwestern Hawaiian Islands.

"Typically, fish are counted and measured with the human eye, with their size estimated by each individual diver. Obviously counting this way leaves lots of room for error," explained Walsh. "Science needs a new way to do this more accurately and lasers may be the next step."

According to Walsh, scientists have been experimenting with lasers for use in estimating fish size for a number of years, with varying levels of success. The biggest obstacles in the past had been cost, range and portability. That was until hand held pointers were developed. Recently, several laser companies began developing underwater laser pointers for use by ocean recreation companies to point out fish and other organisms underwater. But while they served their tour purposes, they were still inadequate for scientific study because, due to light absorption underwater, the red colored light beams could only travel a few feet.

As Walsh and his team began to envision a better laser, they began to look at the possibility of using a green laser instead which can transmit light
farther underwater and are more perceptible to the human eye than red. With that concept in mind, Walsh began contacting laser companies to develop such a tool. To his surprise, one company on the mainland had already started to develop one.

In anticipation of this trip to the northwestern islands, when these new green lasers became available eight months ago, Walsh began to test them underwater in Kona, on the Big Island of Hawaii. They worked rather well but they still had limitations underwater in terms of distance. Walsh's team needed the laser to reach 30 feet or more "for use in big predator country," as Walsh described.

"We began working with the company, Miraclebeam Inc. about three months ago to develop a more powerful laser. They said while such a laser was possible, it would cost more and may be difficult to have in time for the expedition," explained Walsh.

The company was able to create the laser but mistakenly sent the new lasers Walsh had ordered to his colleagues on the Townsend Cromwell (T/C), after
Walsh had spent months working with the company to design the new tool. The T/C researchers had also ordered lasers, but the less powerful ones and
by the time the mix up was noticed, they had already left for the northwestern islands the week prior.

As a result, Walsh is using the less powerful, 5 milliwatt lasers which as he puts it, "is certainly better than nothing." Hopefully Walsh will be able to retrieve the higher powered lasers from the T/C crew when the ships rendezvous at Midway on the 30th of September.

Interestingly, the lasers may prove useful to science in other ways. Walsh says that they've already noticed that certain fishes have different reactions to the fish. Some invertebrate eaters think the light beams are prey and chase the light. Using these beams scientists may later be able to determine the feeding territory of certain fish, like hawkfish, that only feed in limited ranges around their coral homes. Potentially even more useful, if these lasers cause a flight response in large fish like sharks, one day there may be a laser 'shark billy' created to make divers feel more secure underwater.

With all Walsh and his team have to do on this expedition, these other scientific inquiries will have to wait.

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