Friday, December 1, 2023

River survey will reveal cyclone’s toll

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Divers will drift down NZ rivers to assess trout population and health of water ways.
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Rivers that were extensively damaged by Cyclone Gabrielle will be closely monitored as part of a nationwide study by Fish & Game aimed at assessing trout populations and river health.

Divers will be used to explore more than 250km of waterways, covering about 100 different rivers throughout New Zealand.

Fish & Game New Zealand chief executive Corina Jordan said staff will drift and glide down rivers, recording water clarity and temperature and assessing fish habitat, the number of native fish, algal growth and the various insects present.

The information from the trout population surveys will be used to help set catch limits for anglers.

On the back of Cyclone Gabrielle, Jordan said the organisation is most concerned about rivers and streams in the Hawke’s Bay and Gisborne areas and will be monitoring these closely.

“We’ve been meeting with our managers to consider the implications on our species, freshwater and wetland habitats, and the potential impact on recreational users.”

She said the priority is to support those impacted by the cyclone “in any way we can”.  Once things have settled down Fish & Game staff will “look at what the ecological damage is to those river systems and species in them”. 

“If we have impacted rivers – the Tukituki and lower reaches of the Ngaruroro come to mind – then we will be providing information about where they (fishers) can go, where the populations may be intact.”

There have been recent sightings of orca feeding off the coast of Hawke’s Bay, which suggests fish have been washed out to sea, she said.

“If populations in those rivers are impacted, it’s likely to be in the middle and lower reaches. It takes a river about three years before they come back, so it’s quite a quick recovery but that depends on ongoing disturbance during spawning.”

Jordan said the river health programme highlights the important environmental monitoring role of the organisation.

“Drift diving enables us to give rivers a close-up health check. Combined with our assessment of the trout population –  the species that has the highest water quality requirement of any of New Zealand’s fish – these observations will give us a good gauge on how healthy our rivers are.”

Many regions have information dating back more than 30 years, the longest running dataset of its kind, she said.

The drift dive programme is expected to run until April.