Jenny and Tony Enderby: Scuttling for fun, profit and to make fish happy

The decommissioned frigate HMNZS Canterbury comes up for tender this month and will either be cut up for scrap or sunk as an artificial reef.

In November last year, another frigate, the Wellington, was sunk in little more than 20m of water off the capital's south coast with the support of Tourism Wellington and regional and local councils. The sinking was accompanied by fireworks and watched by huge crowds.

The first big Cook Strait storm this year broke the Wellington into three and debris was strewn along Titahi and Owhiro Bays. But it is still a diveable wreck and locals and visitors are still flocking. Tourism benefits to Wellington outweigh any negatives.

Europe's first artificial reef was created in 2004 when the environmentalist Dr David Bellamy pushed the plunger, setting off explosive charges on the ex-Royal Navy frigate Scylla, near Plymouth.

Marine scientists, backed by Britain's National Marine Aquarium, will monitor the growth of marine organisms on the ship. Local and visiting divers will have a new wreck to explore in addition to a World War II wreck a mere 500m away.

Former naval vessels have been sunk off Queensland, South Australia and Western Australia. The most recent, the destroyer Brisbane, sunk off Mooloolaba on Queensland's Sunshine Coast in July last year, attracted thousands of divers in its first summer.

Intentional sinking of ships in New Zealand is not new. From the 1920s old ships were towed to the entrance of Otago Harbour and sunk beside the Aramoana Mole breakwater to help strengthen it. Some of those hulks still provide a haven for invertebrate life and fish schools as well as a site for scuba divers.

In the Hauraki Gulf, most boaties are aware of the hull of the sailing ship Rewa, scuttled as a breakwater in the lee of Moturekareka Island. Hulks on Rangitoto and other islands have all but vanished.

There was no thought of providing a haven for marine life with these ships. They were just dumped somewhere out of sight. Unlike the purpose-sunk wrecks of today, they met no safety requirements.

Now all oils, heavy metals, asbestos and other contaminants must be removed to get resource consent. But the problem of them breaking up too fast remains.

New Zealand has had more than 2000 recorded shipwrecks. Those in exposed areas less than 30m deep break up and vanish quite quickly. In sheltered situations and in water deeper than 30m, they often last more than 100 years.

The Greenpeace ship Rainbow Warrior was the first of the modern purpose-sunk wrecks. It was raised from Auckland Harbour and resunk in Matauri Bay in Northland in 1987. The wreck quickly became covered in bright sponges, anemones and other invertebrate life. This in turn attracted fish schools which fed over and around it. Divers from all over the world visit, mainly due to the wreck's history and reputation as a colourful dive site. After nearly 20 years underwater the hull is still largely intact, due to the protection from Pacific Ocean swells afforded by the Cavalli Islands.

The research vessel Tui, sunk north of Tutukaka Harbour in 1999, was followed in 2001 by the frigate Waikato a few kilometres south. Both were sunk in more than 30m of water but Pacific swells pounding the exposed Northland coast have begun to break up both ships. Yet divers still flock to them, enjoying the marine life and fish schools around them.

A World War II tugboat, the Taioma, sunk in the Bay of Plenty in 2000, is still almost intact. It is covered in life and supports schools of resident fish. It has the protection of Motiti Island, which deflects the worst of the Pacific Ocean swells.

The Canterbury's potential tourism and economic benefits have attracted the interest of syndicates from around New Zealand.

Which leaves the question of where the frigate should be sunk. Obviously the province it is named after should have first choice but no suitable site exists along the Canterbury coast.

Auckland has the largest number of scuba divers in New Zealand but no safe, accessible shipwreck. Most of the inner Hauraki Gulf lacks the visibility to be a safe wreck site because of silt running off the land and discolouring the water.

Omaha Bay is the ideal site for the Canterbury, being more than 30m deep and protected from the worst Pacific Ocean swells by Little and Great Barrier Islands and the Coromandel Peninsula. The increasing price of petrol means divers' budgets are reduced and a dive site little more than an hour from Auckland is appealing.

A survey of the Omaha Bay site by marine biologist and long-time scuba diver Dr Roger Grace showed there would be minimal impact on existing marine life.

Dr Grace's view was that within a short time large schools of fish would appear over the wreck and the hull would become densely carpeted with marine life. The ship would have a useful life as an artificial reef for future generations of scuba divers.

Benefits to the Rodney and Auckland areas from the Canterbury as a dive site would be enormous. Omaha Bay is a natural marine amphitheatre with vantage points around the coast on both sides providing suitable areas for watching the ship sinking.

Seeing a large ship vanish beneath the waves accompanied by a pyrotechnic display is a once-in-a lifetime event for most people.

It just needs the positive support from Auckland and Rodney people and councils that was given to the Wellington project, to make it happen.

* Jenny and Tony Enderby are authors and photographers specialising in the marine world.