Keeper size and quantities are easy, just go to the California Fish and Wildlife website.
As for the safety of eating fish in the Imperial Beach area today, given the fairly massive runoffs of sewage and repeated warning, I would say skip any bottom eating species (croakers, perch, flatfish, etc.) and while the pelagics such as mackerel may be safe it might just be best to leave them all alone at this time. If you do decide to eat some please follow the advice in my book on preserving, cleaning and cooking the fish, it will lessen the dangers.