Weather hampers seabed post-cyclone research

A109 Light Utility Helicopter flight with mayor Gisborne City from the air in November 2023.

Scientific research into Cyclone Gabrielle’s effects on the seabed around the Gisborne coast has been largely thwarted by more bad weather.

The National Institute of Water and Atmospheric Research (Niwa) is studying the ocean off Tairāwhiti and Hawke’s Bay to see how Cyclone Gabrielle has impacted the health of fisheries habitats and seabed ecosystems, through the influx of silt from the land via rivers, increased ocean mixing, and re-suspension of sediments from the sea-floor.

However, project leader Dr Daniel Leduc yesterday told The Gisborne Herald  weather and sea conditions had been so bad survey equipment had not been able to see anything at shallow depths.

“Assessing the impacts of the cyclone on the seabed ecosystems off the Gisborne region has been challenging,” Dr Leduc said.

“The weather was pretty bad when the Niwa team was there back in June, which meant they could not see anything on the video transects conducted closer inshore ( at about 15 to 30m water depth) because of too much suspended sediment.

“Further offshore (30-80m water depth), the seabed ecosystems looked OK.

“At this stage, we don’t have enough information to assess potential impacts of the cyclone on the inshore seabed ecosystems in the Gisborne region. This is also made difficult by the lack of pre-cyclone data, which prevents us from making comparisons.

“We are hoping that the weather conditions will be better during our next voyage later this month.”

A key output of this work is to develop models which will help determine where this sediment has ended up. This involves analysis of sediment using tools like satellite imagery, but also through several sea voyages throughout the year to collect samples of the sediment, obtain video footage of the sea-floor, and map it using sound-waves.

To the south, around Hawke’s Bay Dr Leduc said the crew observed encouraging signs of life in the sea floor sediment cores, such as sand dollars, hermit crabs, juvenile shellfish, and sea cucumbers.

“These are important parts of the food web, and their presence could either mean that they were able to survive the increased sediment or that the sediment did not collect in these areas,” Dr Leduc said.

Fisheries New Zealand commissioned Niwa to conduct the research and will use the information to help understand implications of the cyclone for local fisheries.

Niwa is also about to begin another project on cyclone impacts focusing on coastal ecosystems at less than 15m water depth, funded by the Ministry of Business, Innovation and Employment.