The sea birds are feasting on the swimming crabs at Southshore beach. They are also an important food for whales and other sea life.
Otago University marine science professor Steve King said the summer stranding is nothing to be alarmed about.
"It's a natural cycle of the pelagic food where climate change is happening but it is mostly manifested in the warm water conditions we are seeing right now.
"There's a raft of red-pink animals on the wave wash on the beach, that's a very typical thing to happen in the summer time in these sub-antarctic waters."
King said the red crabs have a pigment which reflects the pink colour.