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Image of fisheries biologists at work.

Hundreds and Thousands and Millions of Fish

Young Naturalists learn how biologists

measure fish populations in lakes and rivers.

by Roland Sigurdson

Minnesota is home to millions of fish. From a darter the size of your pinky finger to a lake sturgeon as big as a high-school linebacker, every fish in the water is part of a food chain. Small fish eat plants and bugs in the lake or river, and then bigger fish eat smaller fish. Anglers cast their bait to catch a fish. The lake or river where you fish is called a fishery.

Scientists called fisheries biologists work for the Department of Natural Resources. They study how all the fish in the food chain connect to one another. They try to figure out which fish species live in a lake or river and how many fish make up the population there.

To count how many people live in the United States, the government conducts a census, or survey, every 10 years. To estimate how many fish are in a lake, DNR fisheries biologists do a fish survey about every five years. Surveys can also show how fast the fish are growing, how many new fish survive after hatching, and how many fish anglers are catching. All of this information, or data, helps fisheries biologists decide how many fish anglers can catch without harm to a fishery.

Biologists look for answers to other questions such as these: Should anglers be allowed to keep fish of only a certain size? When is the best time, or season, to keep fish?

The rules for catching a fish on a lake are called regulations. This story tells how biologists decide what kind of regulations fit best for different lakes or rivers.

To read this entire Young Naturalists story, download the PDF below.

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