Researching what fairy tern eat – what fish will they find in Mangawhai Harbour?

Ian Southey’s fish study was undertaken on behalf of the New Zealand Fairy Tern Charitable Trust. It involved taking samples of fish at four fixed locations in the harbour at monthly intervals, with a view to establishing what fish were there and how they varied over the seasons.

What’s in the net?

Once every month the same four sites in Mangawhai Harbour were visited around low tide. At each site three drags of the net were done and the contents collected, identified, counted and measured. The catch was then returned to the water to continue growing.

The study started in October 2017 and finished in January 2020.  There were 28 monthly sampling sessions covering three breeding seasons.

Gobie – magnified

Most of the fish caught were gobies, which have been confirmed as making up roughly 80% of fairy tern diet (Ismar et al 2014). 48,603 gobies were caught in the course of the study.  Next most numerous were flounder (643). Others identified were tiny mullet, estuarine stargazers, whitebait, snapper and parore larvae, a tiny red gurnard, a spotty and clingfish. All fish caught were identified and counted and, where possible, their total lengths were measured as quickly as possible prior to release. Samples of unidentified species were retained and taken to Auckland museum for identification by Dr Tom Trnski.

Counting, measuring and recording the catch