Adult whitebait kōaro spotted in Pākuratahi Catchment, Napier

The at-risk adult whitebait kōaro has been spotted “in good numbers” outside its preferred native-forest habitat in Hawke’s Bay.

Results from recent environmental DNA (eDNA) sampling in the Pākuratahi Catchment, about 20km north of Napier, which compared instream life from neighbouring native forest, pine forest and pasture catchments, found that the pine forest stream harboured fish and bug species “comparable with the native forest stream”.

The native fish species kōaro was found in good numbers in the native and pine streams, but were not detected in the pasture stream.

Kōaro, one of the five species whose juveniles are known as whitebait, is rare on the East Coast as it prefers forest cover, typically found more inland.

Pan Pac environmental advisor Dan Fake said lowland native forests are a very rare ecosystem type on the East Coast of New Zealand, south of the East Cape.

Consequently, fish like kōaro which prefer cool, clean streams with forest cover are mostly found in the inland ranges.

“Lowland radiata pine forests can provide similar aquatic habitat conditions to that of native forests – they filter nutrients and sediment, provide habitat complexity and generally have cool clean water – all conditions that many sensitive native aquatic species prefer,” Fake said.

The samples were the first round for the Pākuratahi Land Use Study Part Two – a joint project involving Pan Pac, New Zealand Forest Owners’ Association, Hawke’s Bay Forest Growers, Scion, Ministry for the Environment, MPI and Hawke’s Bay Regional Council.

A Department of Conservation spokesperson told Hawke’s Bay Today that while the optimal habitat for kōaro is native forest, they do occur in pine forest.

“In pine forest they are more vulnerable to increases in sediment and slash when harvesting occurs. These adverse effects can be reduced with native riparian setbacks within pine forest and conditions to reduce sediment and slash inputs to the stream.”

The spokesperson said the occurrence of kōaro in pine forest does not necessarily mean they are being “pushed” into these habitats.

“In some regions they may have native and pine forest available; in other regions there may only be one or the other forest type. Much of the lowland native forest has been removed, for example, from around Hawkes Bay.

“If there is only pine forest available, a human-induced change to the habitat, kōaro no longer have a ‘choice’ of which habitat to occupy.”

The first Pākuratahi Land Use study, published in 2006 analysed water samples, hydrology, stream morphology and stream ecology from two neighbouring catchments ― the Pākuratahi and Tamingimingi ― over a 12-year period.

These two catchments had differing land uses with the Pākuratahi being radiata pine, and the Tamingimingi being sheep and beef.

Fake said the study found that forestry had the lowest overall yield of sediment even when the sediment discharge during harvest was taken into account.

He said part two of the study will monitor the two catchments captured in the 2006 study, as well as a nearby native forest catchment owned by Pan Pac. It will also capture the second rotation harvest of trees in the Pākuratahi catchment, using new techniques like LIDAR and eDNA to measure sediment yield and changes in stream biodiversity.

Last year a whitebaiting rāhui [restriction] was placed on a large chunk of Hawke’s Bay after Cyclone Gabrielle damaged much of the habitat.