I've said for years that if a fish size limit is imposed it should be a maximum size or a slot. The same thing applies to antler size limits, allowing harvest of only the biggest just means that the runts become the gene pool.
Been told I'm wrong on both counts by "experts".
Not too surprising I suppose. While I can't speak to the shyness component, I did have a professor (about 20 years ago now) that observed similar size trends in Tilapia at a long term study site in Africa. His research was conducted on a relatively small lake with an agrarian community that supplemented their diet with Tilapia collected in gill nets. Over the course of his time working at the study site, the Tilapia population in the lake actually decreased in size significantly. Where the population originally had a median adult size in line with populations found in other lakes in the region, that median adult size had declined to the point where it was slightly smaller than the openings in the gill net by the time I was taking his class.