Snapper is the predominant fish species in the Hauraki Gulf and it is also one of the most widely studied fish species in New Zealand. Snapper are slow growing and long lived, potentially reaching up to 60 years of age and 17 kilograms in weight.
The adult fish are extremely productive. They spawn many times over the warm summer months, with smaller fish producing tens of thousands of eggs and larger fish producing several million eggs, each season. The older fish are therefore important for their spawning potential. As well as producing many more eggs, their eggs are larger, which likely improves the survival and growth of their offspring.
Recent research has identified a significant difference between snapper that live around shallow rocky reefs and those that live further afield. The reef-based snapper appear to be largely residential and therefore they are susceptible to being fished out of local areas. In contrast, snapper that live over soft areas of seabed range much larger distances and are therefore more resilient to localised depletion. This suggests that fishing off reefs should be undertaken with care.
One of the most direct threats to a healthy snapper population in the Gulf is overfishing. It is thought that harvesting reduced the snapper population to as little as 10 per cent of its original size in 1988, before it increased to around 24 per cent in 2010, and then again went into decline.
Habitat degradation from sedimentation and bottom disturbing fishing practices such as trawling have also likely affected the ability of the snapper population to rebound. This is due to the loss of habitats such as sea grass, shellfish beds and sponge and coral gardens which enable juvenile fish to survive into adulthood.