A brief explanation of catch per unit effort (CPUE), proportional stock density (PSD), relative stock density (RSD), and relative weight (Wr).

Catch Per Unit Effort (CPUE) is the catch of animals in numbers or in weight taken by a defined period of effort. Can refer to trap-net nights of effort, gill-net nights of effort, catch per hour of electrofishing, etc.

Proportional Stock Density (PSD) is calculated by the following formula:

PSD = Number of fish > quality length x 100

Number of fish > stock length

Relative Stock Density (RSD-P) is calculated by the following formula:

RSD-P = Number of fish > preferred length x 100

Number of fish > stock length

PSD and RSD-P are unitless and usually calculated to the nearest whole digit.

Size categories for selected species found in Region 3 lake surveys, in centimeters.

Walleye 25 38 51 63 76

Sauger 20 30 38 51 63

Yellow perch 13 20 25 30 38

Black crappie 13 20 25 30 38

White crappie 13 20 25 30 38

Bluegill 8 15 20 25 30

Largemouth bass 20 30 38 51 63

Smallmouth bass 18 28 35 43 51

Northern pike 35 53 71 86 112

Channel catfish 28 41 61 71 91

Black bullhead 15 23 30 38 46

Common carp 28 41 53 66 84

Bigmouth buffalo 28 41 53 66 84

Smallmouth buffalo 28 41 53 66 84

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PSD values within the target range indicate a balanced population. Values less than the target range indicate a population dominated by small fish and values greater than the target range indicate a population comprised mainly of large fish.

Relative weight (Wr) is a condition index that quantifies fish condition (i.e., how much does a fish weigh for its length). When mean Wr values are well below 100 for a size group, problems exist in food and feeding relationships. When mean Wr values are well above 100 for a size group, fish may not be making the best use of available prey.