Since Gotham is a city directly on the Atlantic Ocean, they occasionally get some marine visitors. It's not a daily occurrence, perse, but once in a while you can find any number of aquatic mammals along Gotham's coast. More specifically? Seals.
However, because this is Gotham, and nothing is ever just normal and fun here, this can occasionally be a problem.
On the rare occasion that a seal ends up coming onto land from the Gotham Harbor-- usually Harbor seals coming to haul-out on land after their swim south from Canada in the late fall, or even to have their pups during the Spring-- there usually aren't the resources to make sure they're safe. Gotham animal control is usually busy with any number of rogue related creature problems (Penguin's trained birds, Harley letting her hyenas out again, etc), so a seal or two who wanders into an urban area and maybe puts themself in danger of cars/humans/etc isn't a major concern.
Well-- it's not a major concern to most. And Bruce Wayne is not, by any means, most.
Bruce couldn't help himself, really-- as Batman, it's his responsibility to help all of Gotham's residents, and if that happens to include a pinniped on any particular night, then so be it. He trained with a number of different Marine Biologists across the planet, and eventually collected the skills to safely and efficiently handle a seal.
So now, every once in a while, a call will come in that a seal of some kind has made itself at home on the docks, and Batman always makes sure to swing by the area and ensure that the creature is comfortable and safe-- and he puts up warning tape to keep civilians away, just in case.
(Bonus: All of the Robins and Batgirls were also, at some point, trained in seal handling, and Bruce eventually found that it's actually very effective to deal with a cranky teenager by sending them to go "monitor the seal activity", aka sit in silence by the water for an hour or two until they stop throwing a tantrum about whatever they're mad at him about.)
