This InfoSheet is number: 1038
Summary: Game Wardens use a $30K fishfinder to determine health of various fish species in Maine Lakes
‘They Drive By Night’ by Linda Price (Maine Fish and Wildlife) Winter 2001
I’m revealing my age, but “They Drive By Night” is an old Humphrey Bogart movie about truckers fighting lack of sleep and lack of good headlights to stay on course. Personnel from Maine’s Department of Inland Fisheries and Wildlife who are operating new hydroacoustic equipment have those things in common with the old-time truckers. Most of the work must be done during normal sleeping time and the course can’t be seen well.
The new equipment is one of the best tools available for measuring populations of smelt and other fish. Ultimately, in the years to come, the data gathered by the high-tech sonar equipment may change the way salmon are stocked and managed in Maine waters.
Measuring smelt populations is best done on summer nights when the fish break out of their schools on the bottom of the lake or pond and swim as individuals through the water. Fisheries biologist Rick Jordan, who’s headquartered in the Division’s Machias office, is responsible for the Department’s smelt species plan, which he wrote more then 20 years ago. Jordon, who started out as a pre-med student at Wheaton College in Illinois, switched to biology at the University of Maine at Orono. Fisheries courses he took there have determined his career path, and he’s been with the Maine department since 1973. “Each of the individual fisheries biologists is responsible for one species,” he explained. “One of the parts of the plan is identifying problems in management, and another is that smelt are a cyclical fish...they will be abundant for a while and then the population will crash”.
“But, we had no way to measure the smelt populations, only indirectly by getting samples of salmon. If they were long and heavy we figured there was good forage...plenty of smelt,” he continued. ”By the time you get skinny, short salmon, the problem with the smelt is already advanced.”
In the early 1980s, he learned that hydro-acoustic [literally, water sound] equipment was available, but with a $100.000 plus price tag. Advances in technology began to bring the price down, and three years ago he wrote a grant proposal for Maine to acquire the equipment, which is manufactured in Seattle, Washington, and now costs about $30.000. “The technology originated from the west coast where commercial fisheries created a big need for accurate, high quality equipment especially in counting salmon runs,” Jordan explained. The money came from Maine’s Outdoor Heritage Fund.
A main component of the equipment is the transducer, which is seven inches high and about 10 inches in diameter. It is mounted, pointed downward under a four-foot-long steel sled-like devise called a “biofin” which has runners or skids on the bottom to progect the transducer if it should be towed over a rock or a shallow bottom. The transducer, attached to the four foot sled, is suspended and towed in the water at about three feet deep from a davit arm attached to the side of the cabin of the outboard boat...it’s like a crane with a pulley to raise and lower the biofin which looks like an ocean sized planer with fins in the back to make it track properly without banging into the side of the boat.
“I believe the Warden Service was using the smallish former lobster boat to check coastal duck hunters,” Jordan said. “But I think the all-white boat was a little too obvious to use to check duck hunters, and it became available for our use on the lakes.”
Jordan and a summer assistant, Dan Bowker, did the work attaching the equipment to the boat. Bowker, who had a just graduated from Unity College, helped “more than he knows because of his positive attitude,” Jordan said. “The davit arm for the transducer was challenging to rig, but Bowker was steadfastly confident that it could be done.”
The transducer is cabled to a laptop computer, and the whole outfit functions much like a supersensitive fishfinder. The transducer generates sound at 200 kilohertz, which Jordan described as “a pulse, 200/1000ths of a second long.” Interestingly, the speed of sound in water is from 1400 to 1500 meters per second. The computer has a data analysis program that accepts the information the transducer receives during the trip of the sound pulse, down and back. “The sound pulse is reflected off what it hits and comes back to the transducer. If there are no fish, it goes all the way to the bottom and back,” Jordan explained. “Each fish is measured by the volume of its echo” [that actually comes from its swim bladder, an air sac inside the fish that helps it adjust it’s depth in the water column]. Big fish, big swim bladder, big echo.
“Each echo is measured in fractions of a decibel [a volume of sound], which accordingly tells the computer the size of the reflecting fish and the computer decides what color to display on the monitor. The depth is measured by the time the sound pulse takes to go down and back,” he continued. “It’s all displayed in color according to the size of the fish, as it all feeds back into the laptop and onto the monitor.” For example, red colors indicate the biggest fish - no one has seen a red one yet. The next biggest size, some blue and green, were spotted on the West Grand Lake [probably togue]. Smelts show in violet color. The Department has used the equipment on Maranacook, Sebago, Thompson, Tunk, Cathance, Rangeley, Schoodic and East Grand Lakes so far.
“It’s really challenging, kind of like instrument flying in a simulation booth,” said fisheries biology specialist Greg Burr, who has logged about 90 hours in the boat after dark. “You’re in a dark booth with just a gauge, bobbing in a lake in the dark.”
Jordan agreed the work was challenging but emphasized that everyone who’s tried it has found it fun and rewarding too. “The challenge is to be out there at night, going around islands and boulder shoals, trying to follow our course along transect lines,” Jordan said. ”We use a Global Positioning Satellite system and maps to draw our transect [course] lines and to plot locations of various waypoint numbers.”
The work must be done at night...in the summer, smelts school up close to the bottom during the day. Such a school would give off a huge echo to the transducer if we used it during the day...and it would be impossible for the machine to use that echo to determine how many fish were in the school. At night, the smelt break out of their schools to feed individually on plankton.
“It was so interesting on West Grand Lake. Just about nothing showing during the day,” Jordan recalled. ”Then, by 9:15 p.m. they were scattered all through the upper 30 to 40 feet. It’s interesting to see the pattern of how they move. They move like that because plankton and insects do the same thing,” Jordan said. “It’s a whole different world out there.”
It wasn’t always smooth sailing. Jordan remembers calling the manufacturer in Seattle on a cell phone from the middle of Cathance Lake on an exploratory mission. But, in an hour things were working perfectly.
Several things, in addition to great tech support from the manufacturer, have contributed to the successful use of the equipment. Jordan has held training sessions for at least 10 other fisheries biologists. They practice using the transect lines in the daytime to develop confidence and skill. Jordan also realized that users would need a written set of instructions, which he has since developed. The text is 10 pages long and includes information on every detail that could arise, from the launch of the heavy boat to the set up of the transducer and laptop.
“ I used a little tape recorder, which I took everywhere and when thoughts came about instruction I spoke into the recorder,” he said. “I wanted everyone to be able to use the equipment on their own after training, without me looking over their shoulders.” The only disadvantage to the equipment is that it doesn’t differentiate between smelts and other species of small fish.
This can perhaps be overcome by comparing lake data to small sample of known fish. Smelts usually account for about 80 percent of the small fish in our lakes, Jordan explained. “I hope that the angling public is patient and realizes that it will take time to develop a string of data from various lakes, long enough to show a trend,” he said. “In Maine, smelts are the most important food to landlocked salmon. We need to do everything we can to manage their populations. This new equipment is the best tool we have.”
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