It seems appropriate to be writing about water as the rain falls yet again. I imagine all the 30-plus streams on Hauturu will be flowing freely at this time of year. Hauturu provides a virtually unmodified example of native forest stream habitats and possibly some of the cleanest stream water in the country.
The numerous streams on the island are largely ephemeral, meaning they only flow during and immediately after local rainfall, transforming, it seems, from raging torrents to isolated pools almost overnight. They mostly flow from the high central peaks over numerous waterfalls, where the hard, volcanic rock erodes much more slowly than the soft overlaying volcanic breccia (broken, fragmented rocks of volcanic origin), then travel on to the sea through picturesque narrow gorges covered in drooping ferns and plants. Most streams consist of various sized boulders and pebbles, and steep stream-sides with overhanging native vegetation. The vegetation helps to keep the stream temperature more even.
Debris from leaf fall, rotten logs and flooding forms an important component of the streams too, providing food for some stream creatures and a haven for others. Several of the streams on the southern, less rugged, side of the island open out to wider boulder streambeds. Their form changes with each heavy rainfall.
The majority of streams find their way into the sea travelling beneath the boulder beach that surrounds much of the island. In dry weather, parts of the streams seem to disappear beneath the boulders and pebbles of the streambeds, though often the trickle of water can be heard. In these conditions the only visible water are pools of varying sizes.
Despite the extreme variation in water flow there are many creatures that are adapted to this existence. There are banded kokopu (a native fish species) and longfin eel in a number of the streams, as well as a large variety of invertebrates (insects). There are known to be some 33 species of invertebrates that spend at least some of their life cycle in the Hauturu streams, mayfly and caddisfly larvae being the most common. The adults of these species briefly become winged creatures for the purpose of mating. Their young hatching in the streams as larvae and the cycle continues.
Many of the other island residents (birds and reptiles and the odd human) use the streams for drinking and bathing, some for feeding such as the kingfisher, and some like the moist stream bed to live near, such as the rare chevron skink that is found only on Hauturu and Aotea (Great Barrier). The vegetation in the river valleys is often more varied and lusher than that on the drier ridges.
The streams on Hauturu are an integral part of the island tapestry and part of what makes it such a special refuge for New Zealand’s unique plant and animal species.
The Little Barrier Island (Hauturu) Supporters’ Trust through Natural History New Zealand has produced a short video showcasing the incredible biodiversity of the island. “Hauturu: New Zealand’s Ark”. This can be viewed here: youtu.be/_oNir75_l4U
The Trust is grateful to the Becroft Foundation for funding this project.