From a recreational fishing perspective, nobody wants to see WSB gill-netted, but there has to be some perspective applied to this situation. Without adequate information on WSB stocks the DFG would not be able to properly manage this fishery. Like it or not, the use of gill nets provides researchers with a standardized method of measuring WSB populations. Diver observations and commercial/recreational catch reports provide some anecdotal information but it is not as precise as using nets. The use of nets for sampling is, obviously, not a perfect method, but it is more accurate than other methods. They aren't just throwing nets out to kill everything that swims by. The nets used have specific mesh size, overall size and are laid at known locations in a specific orientation. This allows the researchers to compare results of samplings taken over several years. This is the most accurate means of obtaining VALID population data. Also realize that this is not the only data collection method that is being used.
Take some time to look through some studies of WSB populations. You will understand that there is a reason for the data collection methods. They have been using these sampling techniques for years and they have documented that the WSB stocks are recovering. It is obvious that the sampling is not killing off the species.
http://www.dfg.ca.gov/mlpa/response/white_seabass.pdf
http://departments.oxy.edu/vrg/publications/pdfs/Craig%20et%20al%202004%20CMJ.pdf 
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http://departments.oxy.edu/vrg/publications/pdfs/pondella%20and%20allen%202000.pdf