By Paul Caiger.
Imagine a piece of New Zealand coastal paradise where the native bush and all its terrestrial inhabitants are left to regenerate without the pressure of exotic predators. Where the marine realm is allowed to flourish without the pressures of fishing and harvesting.
And all of this less than an hour from the country’s largest city. This is the case at Tawharanui Peninsula on Auckland’s northern coastline.
The site of Maori settlement for around 800 years, Tawharanui provided a bounty of forest and marine resources, and is celebrated in the saying “He wha tawhara ki uta; he kiko tamure ki tai” – “The flowering bracts of the kiekie on the land, the flesh of the snapper in the sea”. For many, the chance to see kiekie is limited, as possums have an insatiable taste for this fruit. Likewise, outside of our marine reserves, not many New Zealanders would get to see large resident snapper or a cave bristling with crayfish antennae.
Approximately 12km south from the better-known Goat Island (Cape Rodney-Okakari Point Marine Reserve) to the north, Tawharanui Marine Reserve protects a similar slice of our coastal oceans. A marine park since 1981, it was granted full marine reserve status in late-2011, becoming the country’s 34th. One of the most conspicuous advantages to the marine reserve is the major increase in spiny rock lobster or crayfish numbers since the area was declared a marine park in 1981. Long-term monitoring from Dr Roger Grace since the 1960s has charted the steep rise in numbers to the current decade, from around one cray per 500m2 to over 35 per 500m2 now.
Furthermore, crayfish monitoring programmes show there to be more crayfish per square metre in the Tawharanui Reserve than at Goat Island, the older and more eminent cousin further up the coast. The 2009 surveys estimate that just 3.5km of reserve would be equivalent in crayfish numbers to 40km of non-reserve coast! There is a caveat, however, with results from the most recent survey showing a marked decline in numbers, coinciding with anecdotal evidence from the local commercial crayfish fishermen that numbers are well down in recent seasons.
Perhaps the sustained fishing pressure on the nearby surrounding areas, both commercial and recreational, are beginning to take their toll, even within the protected coast. Moreover, crayfish are highly gregarious; that is, they like to hang out together. If adults are thin on the ground, then perhaps the juveniles are less inclined to settle in suitable habitat. The reality is, there is much we have yet to learn about the recruitment processes of crayfish (and in fact most marine animals), especially given their larvae drift on oceanic currents for up to two years!
Through the constant presence of scientists at Goat Island, much has been learnt around the response of the reef to protection over time, with a shift in the ecosystem through what is known as a ‘trophic cascade’. Not being an overnight occurrence, the early stages of protection leads to increases in conspicuous animals such as snapper and crayfish. These check populations of prey such as urchins, and in turn the urchin’s food source, algae, is released from being grazed to barren habitats. In the case of Goat Island and now at Tawharanui, there has been the shift of large barren areas to kelp forest. The forests provide structure for a plethora of invertebrates and both juvenile and smaller cryptic fishes.
What sets Tawharanui apart from most other marine reserves is the extension of protection onto the land, seamlessly merging conservation efforts from sea to sky. With the construction of a 2.4km long predator fence isolating the peninsula, and along with the tremendous support of a largely-volunteer army, the park has bounced back spectacularly. Translocations of several birds and reptiles, many species such as North Island brown kiwi, saddlebacks and forest and green geckos are now breeding here successfully. Other birds such as kaka, bellbirds and grey-faced petrels have recolonised on their own. The mass planting of native plants, in particular around streams and valleys, has seen the natural balance returning even in company of modestly stocked sheep and cattle; the link between the ocean and the forest hardly more evident than the numbers of amphidromous galaxiids seen in the streams of the park. Recent additions to the park include one of the world’s rarest birds, the takahe, and a fake gannet colony, with the hope of attracting the real thing – seabirds also providing a conduit of oceanic energy onto the land. In time, hopefully these native animals will spread to the surrounding areas on their own accord.
Balancing the management of resources along with conservation and ecosystem health is always a difficult task. However, a network of marine reserves spaced apart to capture the movements of the more mobile animals and also larvae, whilst keeping gene flow high, has often been proposed as the sound decision. If this country is set on keeping to its goal of protecting at least 10% of New Zealand’s waters, then setting aside 10km out of every 100km of coastline seems a good place to start! For now however, Tawharanui is a jewel in New Zealand’s crown, and a place where all can go to see some of our natural marvels in all their splendour.