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TECHNICAL INDICES USED IN GFP LAKE SURVEY REPORTS

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.

Species Stock Quality Preferred Memorable Trophy

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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.

Protect our Waters

You can do your part for the health and productivity of South Dakota's waters by being proactive in preventing the spread of invasive plant, fish and animal species that threaten to crowd out native species.