Known widely as the Kelp Gull, and to those in NZ as the Southern Black-backed Gull.
This is the largest species of gull in New Zealand.

The Kelp gull is a rather wide spread species, found throughout much of the southern hemisphere.
In NZ they have become so successful, they're actually only 1 of 2 native species that have no protection under the wildlife act.
This is because their population has boomed since human settlement, and being a predatory species they are causing issues for other threatened and endangered species of shorebirds (such as Black-billed Gulls and various plover species).

Kelp Gulls will scavenge just about anything, from washed up sea stars to pigeon roadkill.
They're essentially apart of nature's clean up crew.

However they do prey on live animals and are known to eat chicks of other shorebirds.