The paradox of the Hauraki Gulf snapper population: Testing the nursery habitat concept

Juvenile nursery habitats are a critical requirement for the maintenance of some fish populations. Snapper in northern New Zealand is hypothesised to fit this nursery habitat model; however, nursery habitat association and dependency are poorly understood for New Zealand's largest snapper population in the Hauraki Gulf. To better understand habitat usage by post-settlement snapper and identify potential nursery habitats, we surveyed fish communities across a range of structured benthic habitats using fixed-position seabed cameras in Kawau Bay, in the northwestern Hauraki Gulf. Results indicated a low overall abundance of post-settlement snapper, relative to previous surveys at a nearby harbour outside of the Hauraki Gulf. There were also amongst-habitat differences in Kawau Bay, with post-settlement snapper and fish diversity higher in association with horse mussels relative to bare sediment. We anticipated high abundance of post-settlement snapper at restored green-lipped mussel bed sites, but abundance was again low relative to previous surveys outside of the Gulf. While Hauraki Gulf locations other than Kawau Bay may serve as nursery habitats with abundant populations of post-settlement snapper, another possibility is that post-settlement snapper habitat may not be as limiting within the expansive semi-sheltered Hauraki Gulf (potentially following an Effective Juvenile Habitat model). This hypothesis requires further investigation, as the answer could alter the emphasis of habitat conservation and restoration efforts in the area.