Scientists have identified an ‘ecological bottleneck’ in the ability of juvenile snapper to survive into adulthood. Research has shown that young snapper prefer three-dimensional habitats on the seafloor, particularly seagrass meadows but also horse mussel and sponge beds. It is not known why these areas are preferred, but it is thought that they provide a good source of food, protection from predators and shelter from seawater currents (reducing the need to expend energy to swim against them).
If there is not sufficient area of these habitats available, particularly in places close to important spawning areas, then this creates an ‘ecological bottleneck’ and the survival rate of juvenile snapper is likely to be lower. This has a flow on effect for fish stocks as it reduces the number of snapper that are recruited into the fishable adult population.
In the Hauraki Gulf, the majority of these habitats have been lost over the past 170 years, through a combination of increased levels of sediment and other pollutants entering the marine area from land, and direct damage from reclamation, harbour works, trawling and dredging. Habitat loss is still occurring in important fish nursery areas such as the Mahurangi Harbour.
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.
It was not until crayfish became scare around the shores of the Hauraki Gulf that they obtained any real commercial value. Before World War Two crayfish were everywhere and could be easily harvested amongst the rocky reefs close to Auckland.
“Initially there were sacks coming off Waiheke and North Head. Fishermen didn’t need to travel to get crayfish … the problem wasn’t lack of crayfish. They were everywhere … After the war, crayfish were worth very little, something like thruppence a pound.”
Then things changed. New equipment, such as echo sounders, enabled crayfishermen to locate new reefs to target. Improved gear such as winches enabled fishermen to lift many more pots a day and larger boats enabled them to travel further afield. Once the export market opened up for live crayfish in Japan very high prices could be obtained, reaching over $80 a kilo. This incentivised continued crayfishing even when catch rates plummeted. Recreational divers also target crayfish increasing pressure on the stocks.
“Now catch rates are so poor, at only around a third of a kilo per pot, that crayfishermen are reliant on high prices to survive.”
Scientific models suggest that, prior to human arrival, crayfish were the third most ecologically important benthic invertebrate group in the Hauraki Gulf. However, the impact of fishing activity since then has been so great that they are now considered to be ecologically extinct. Stocks are probably less than a quarter of their original levels.
There has been poor recruitment of crayfish into the Hauraki Gulf over the past 6 or so years, and this has exacerbated stock depletion, as a high level of fishing activity has continued during this period.
This has had flow on effects throughout the food web, as crayfish prey on sea urchins which in turn graze on kelp. When the number of crayfish in a system is reduced, the sea urchin numbers rapidly increase due to a lack of predation and they end up stripping the kelp off the rocks. This results in ‘kina barrens’ which are depauperate of reef life. This is why it is important that crayfish stocks are rebuilt to ensure healthy reef systems throughout the Hauraki Gulf.
Read a Dialogue piece in today’s NZ Herald by Sue, Rod and Zoe Neureuter, the family who acts as guardians of the Noises Islands. Sue Neureuter’s personal Story of the Gulf features in The Story of the Hauraki Gulf.
“Creating a fishing park in a region in such alarming decline brings division where the opposite is required write Sue, Rod and Zoe Neureuter.”
Longlining was introduced into the Hauraki Gulf as a method of commercial fishing in 1912. It replaced the use of single baited hooks and immediately increased catches. Longling involves setting a main line, with numerous branches lines or snoods connected to it, each containing a baited hook. Each line can hold thousands of hooks. The method was quickly adopted and is still widely used in the Hauraki Gulf. It is a labour intensive, hands-on commercial fishing method, which is targeted and can produce very high quality fish.
In the early 1980s a lucrative market for fresh ‘iki jime’ snapper opened up in Japan. This involved spiking the fish in the brain after capture to kill it instantly, and then putting the fish into an ice slurry to rapidly cool its temperature. This resulted in a high quality fish which fetched premium prices. Longline fishermen in the Gulf rapidly adopted the new methods, initially pioneered by Leigh Fisheries.
The fish are transported back to port on the same day, sent to the factory for packing and then quickly flown out to high value markets around the world including Australia, the USA and Europe.
“Thanks to Dave Moore from Wildfish and the skipper and crew of Coral V for taking me out on a great long lining trip. I was very impressed by how hard you guys worked.”
The Hauraki Gulf has an extraordinary wealth of seabirds, supported by its productive marine area, diverse habitats and numerous predator free islands. Over 80 species have been seen in the region which comprises 20 per cent of the world’s total species. Of these at least 27 species breed in the wider Hauraki Gulf region.
Seabirds spend most of their lives at sea; they only come to land to breed. Although many of the birds travel enormous distances, some to the north and eastern Pacific – to waters off Japan, Hawaii, California and Ecuador – others venturing down to the Polar Front, they return each year to breed in burrows on the Gulf’s islands.
Historically, seabirds would have also bred on New Zealand’s mainland, but the destruction of habitats and predation by introduced animals have left the remnant populations mostly on islands. Where once seabirds brought fertility to soils, adding nutrients through the decomposition of guano and dead eggs, chicks and adults, farmers now spread fertiliser, much of it derived from seabird islands elsewhere in the Pacific.
The Hauraki Gulf’s rich seabird population attracts birders from all over the world. Threats to the seabirds include longline fishing hooks (the birds dive on the bait and get caught on the hooks), predators at breeding sites and lack of food through overfishing and depletion of fish stocks, especially bait fish.
Commercial fishers are adopting seabird friendly fishing methods to avoid seabird bycatch which include setting their lines at night, weighting the lines so they sink quickly and running tori lines over the top of the long line.
Thousands of Aucklanders, and people living in other coastal settlements around the Hauraki Gulf go fishing each year. Many people enjoy catching fish from mussel farms located around the Gulf. The farms attract snapper which feed on the growing mussels. The large Wilsons Bay mussel farms in the Firth of Thames now support a growing charter boat industry.
Mussel Barge Snapper Safaris is a small family owned business which operates fishing charters out of Coromandel. The images on this page were taken on one of their excellent trips.
A Celebration of Our Association with this Remarkable Place