I could be wrong, but they do it to gauge the health, average size and numbers of fish in the lake. There are several reasons they do it, those are just a few. Kwin....? Care to chime in?
Not trying to hijack. But why do they Elctroshock?
A) That instagram post was from last April
B) Electrofishing is used to collect fish for research purposes. In the case of the above, it was for a multiple mark-recapture study to estimate the "catchable" LMB population at Perris.