This results in quite excited surges of feeding from large flocks of shags ably supported by dive-bombing terns whenever there is a concentration of food (as above); generally out in the main channel and so it's a bit difficult to get close-up shots without a *really* big lens.
These are mostly spotted shags in eclipse plumage and the smaller white-fronted terns.
It's most likely small crustaceans (krill) that they're feeding on.
These (above and below) were feeding in Sawyers Bay.
It gives me a lift every time I see them.