Since rescues will always be readily available from the wild and little blue penguins aren't particularly endangered, perhaps another good function for captive penguin colonies could be to incubate eggs from abandoned nests in the wild and raise their chicks? This isn't to say that any and all captive breeding of little blue penguins in New Zealand should be halted, just that zoos should be thinking a little more widely about the conservation possibilities.
Unfortunately the issue with unreleasable captive penguins is that they have disabilities which hinder their ability to hatch and rear their own chicks. Auckland Zoo noted this as their reason for hand-raising what remains their sole surviving chick to date. Few birds from their colony progressed to pairing up and laying eggs; and previous chicks had failed to survive in their parent’s care, so staff took a proactive approach and removed the eggs.
Disabilities included anything from vision issues to missing flippers and the latter in particular has been attributed to the reluctance of Auckland’s flock to enter the pool. Their struggle to swim with one flipper makes them reluctant to attempt swimming; and therefore they’re unable to build up the waterproof feathers.
While parents don’t directly teach their offspring how to swim, they play a key role by leading them down to the water etc. which is one of many roles rescued penguins may fail to fulfill, which would ultimately leave their fostered offspring ill-equipped for life in the wild.