Well as for what I would have done, let's just say I would not have jumped in freezing cold water for a rescue My husband and my in-laws would have done what you did and dove right in. However, I know my mom would not have, and 50-50 on whether my dad would have. But that is besides the point
Legally I have no clue (funny thing about attorneys, we are not like doctors who have to know a little bit of everything, our knowledge is very limited ) BUT......my thoughts are the same as Muriel. I would think it is stealing not to give them back.
I would recommend calling animal control and even filing a nuisance complaint. Here are links on how to do that in Orange County, I think you are San Bernardino County but I bet OC can lead you in the right direction.
http://www.ocpetinfo.com/animfaqs.htm
http://www.ocpetinfo.com/barking_dog_info.htm