Swim Up And Be Counted!

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Published on: Oct. 2, 2002

Last revision: Nov. 12, 2010

When I was in high school, my classmates and I often discussed our future careers. Most had hopes of becoming engineers, lawyers, doctors and physical therapists. When I announced that I would be a fisheries biologist, they asked, "What do they do?"

I didn't know enough to answer them very well then, but soon after I had acquired a degree in fisheries biology, I learned that the most fun part of being a fish biologist is counting fish.

Fisheries managers count fish the same way the government counts people during the national census, except that fish can't fill out forms and drop them in the mailbox. Instead, we have to go out and find the fish. This doesn't mean tallying every fish in a body of water. We just take representative samples, and from these we can come up with good information about the whole population. The fish from our samples are released unharmed.

Censusing fish is not just a matter of counting them. Before conducting a fish census, we have to evaluate the targeted species of fish, decide on the size of fish we'd like to sample and learn the habitats they occupy. Timing is essential because different fish species occupy unique habitats throughout the year. Time of year, age, sex, water level, cycles of the sun and moon all influence where a fish may be.

The Shocking Truth

We sample fish populations using a variety of gear and techniques. Since the 1950s, the most widely used method of capturing fish to count them has been electrofishing. We introduce electric current into the water that stuns any nearby fish. They float to the surface and we capture them in dip nets.

Usually, the first question people ask about electrofishing is, "Aren't you afraid of getting shocked?"

Although water and electricity usually prove a dangerous combination, electrofishing is safe - both for us and for the fish - if we take proper precautions. We electrofish using backpack units powered by a battery or from a specially equipped boat that has a generator for power. Current flows between electrodes that are placed in the water. A safety shut-off switch eliminates any risk to the operator, and a control box regulates the electric field to make sure it only stuns nearby fish and doesn't kill them.

After only three weeks as a fisheries biologist, I was going on fish-collecting expeditions. We used a 14-foot johnboat rigged with electrical equipment. Within the

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