I am learning that when the DNR does lake surveys, we rely heavily on age and growth calculations. Biologists take a look at the fish scales on a machine that allows them to trace the growth rings or "annuli". These growth rings show the age of the fish as well as the growth in a given year. With a digitizing pad, the biologist can trace the growth rings and have a program calculate the percentage growth from the area between the rings. Another way to calculate this is to measure similar rings on a bony structure called the Otolith found in the fish's head. Using this method, biologists can check how fish born in a certain year are progressing. Not only do they find out how many of them there are, but they can find out if a fish born in 1998 is growing steadily or if it didn't grow well in 2001 due to lack of food. Then they can alter the bag and slot limits on a given lake so that the fishery is not depleted. For example, if there isn't enough Tulibee for the Walleye population on a given lake, then the DNR can take steps to cut down on the numbers of other predators that might eat the Tulibee. If the fish are growing well, but there aren't that many of them, the DNR can limit the numbers and sizes of fish you can take out of the lake to ensure that in 2005, there will be some large Walleye in the lake.
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