Guys, I have no formula nor a good SIMPLE way of estimating how many fish are in a pond based on how many are observed. I have never seen a good method or technique to do the estimation based on casual visual observations. If there was a half way reliable way to easily estimate numbers then fishery biologists would probably frequently use the technique. I also don't think Dr Dave's Fishery Techniques textbook contains a simple method either. The companion book Inland Fisheries Management discusses several techniques for estimating fish populations.
Several common techniques are used in fisheries and or wildlife management for making population estimates. Precision and accuracy varies depending on several variables.
The techniques are:
1. Counts on sample plots
2. mark-recapture
3. decline in catch per unit effort
Statistics and models are then used to calculate population estimates from the collected data.
Electroshocking is one means of commonly collecting data for the counts on sample plots technique.
