Interesting question and I hope our members respond. I know there have been sporadic reports or large numbers of small bat rays at piers but I would need to do some research in our archives to find the specific piers.
It's one reason I put in the following on my write up of bat rays:
For some reason Stearns Wharf in Santa Barbara sees a lot of small, immature bat rays and they're usually called monkey face rays.
Scientists report that bat rays move into inshore waters to breed during the summer then tend to move offshore in the winter (so guess when they are more likely to be caught from a pier). While inshore, they are sometimes found in large concentrations. At times these bat ray gatherings contain several thousand individuals. The sea bottom holding these creatures must look a little weird and would certainly have a somewhat alien feeling; not sure if it would be more like a black-cloaked Darth Vader convention, a Raider Nation convention, or something even more outlandish (and scary), a political convention.