Technical Indices Used In Western Lake Survey Reports
< backA 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.
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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.