We expect the Inland Fisheries and Wildlife staff to know what species of fish are in what waters, what their approximate age and sex ratio is, and how external activities such as dam building or removal are likely to impact them.
They need to know these things if they are to “manage” the waters so that we fishermen and ladies, and more importantly, our children and grandchildren, have a resource they can use, and that resource stays healthy and sustainable. We pay for these activities through our license fees and the taxes we pay on fishing equipment, boat registrations, milfoil stickers, etc.
But how do they know what the fish biomass is in any particular body of water? One technique that they use is electro-fishing, it is not what you may think. It requires a team effort to do because there are several simultaneous actions that are too much for one individual.I had a chance to participate as a team member when IF&W did a biomass count on a section of the Crooked River, a vital tributary to Sebago Lake and the source of many of its native salmonids such as salmon and brook trout.
The key person, in this case Jim Pellerin, Region A Senior Biologist, assigned tasks to those of us, both IF&W staff and volunteers organized by the Sebago Chapter of Trout Unlimited. The most critical task was assigned to Brian Lewis, an IF&W biologist. He had strapped onto his back a battery carrier, connected to a PVC pipe wand that looked like something a metal detector might use—a loop of metal on the end—which he would pass over a section of the stream.
We would all walk up the streamline abreast with some folks on either side of him. Some of us were netters, others hauled buckets of cold stream water. We all wore rubber hip boots, even though the water was warm, as they protected us from a mild shock. We were tempted at times to reach in barehanded and grab a fish, but you only did that once!
On signal, Brian would turn on the wand and slide it back and forth under the water that was about a foot deep where we were. The resulting electric current in the water would cause small fish to move. You would be amazed how many fish actually live in these waters because without the aid of the electro-wand they would not move, and you would not be able to see them.
Flanking Brian “the Sparkman,” would be volunteers with dip nets that would catch the fleeing fish in nets that looked like pool skimmers. The fish would then be placed into buckets of water and hauled to the shoreline where Jim Pellerin was waiting to survey the fish.
Once the fish arrived at the shore, Jim would administer a mild sedative that would help the fish relax and prevent them from getting too excited and hurting themselves trying to get away from the handlers. He would then examine each fish caught, record their length and weight, determine their species and sex, examine them for any unusual growths or previous damage then deposit them in a holding tank while they recovered from the anesthesia.
After a short waiting period they were returned to the water, none the worse for wear. Most of these fish were in the 3- to 5-inch size range. Larger fish would either depart the area as the entourage approached or were large enough to overcome the light charge and would swim away before they could be netted. It takes a very experienced eye to sort and sex these small fish.
We did this for several hours but because of the density of fish in the stream and its width in the section we were sampling, we only did about a 50 linear yard section of the river. From this sampling IF&W could extrapolate what the density of specific fish were and know how productive the Crooked River is for each species.
This is a manpower and time intensive effort, but it gives a good indication of what is going on in waters where this technique is applicable. In waters such as lakes where the water is too deep for electrofishing, other techniques are used such as sonar sampling and using gill nets suspended at various depths.
Occasionally, the biologists will discover a species they did not know existed in a body of water. These are often classified as “invasive species.”
Some of the invasive fish become forage fish for the native species. Sometimes they take over crowding out native species and forcing declines in species we humans are more interested in such as salmon. <
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