When I visited two years ago, the kelp gulls were not in an exhibit anywhere near as flash is this, it was just a basic pond with low wall I think, and wasn't covered, so they must be injured, as they would presumably have been ex-rehab. Did this enclosure look completely new or just redecorated? I think they were previously near the western grey kangaroos, can't remember exactly.
If you look at another view of these birds on here, one clearly has a large chunk of wing missing, so they are probably non-releasable wild casualties. And how much better to make them into a zoo exhibit than euthanasing them, as is too often done.