June 13th, 2024

Detailed NIWA study reveals impact of Cyclone Gabrielle on New Zealand's marine ecosystems

NIWA's research sheds light on the aftermath of Cyclone Gabrielle, revealing crucial data to support future fisheries management and environmental resilience in New Zealand.

Black coral on Tokomaru shelf reef seen during the October RV Tangaroa voyage and captured by NIWA's underwater camera system. (Photo: NIWA)
Black coral on Tokomaru shelf reef seen during the October RV Tangaroa voyage and captured by NIWA's underwater camera system. (Photo: NIWA)

A comprehensive study conducted by the National Institute of Water and Atmospheric Research (NIWA) for Fisheries New Zealand has mapped the extensive impacts of Cyclone Gabrielle on marine environments in the Hawke’s Bay and Gisborne regions. The research, focusing on the aftermath of the February 2023 cyclone, underscores the challenges posed by increasingly severe weather events on marine ecosystems.

Investigating the aftermath of Cyclone Gabrielle: Utilising sophisticated hydrodynamic models and sediment transport simulations, NIWA assessed the transport and deposition of sediments resulting from the cyclone. This scientific effort was supported by remote sensing data and two research vessel surveys, which mapped changes to the seafloor and collected samples of marine life.

"The findings illustrate significant sedimentation impacts and subsequent ecological disruptions," the report says. These disruptions are likely to affect fisheries productivity and conservation efforts, emphasising the need for effective marine policies and management.

Key findings and regional differences: The study showed that sediment plumes significantly affected the marine areas for about two to three months, with substantial sediment deposition in both Hawke’s Bay and Gisborne. Notably, Hawke’s Bay experienced more pronounced immediate impacts due to its shallower and more sheltered bays, which retained fine sediments longer.

According to the report, while some areas showed signs of ecological recovery by October 2023, the abundance and diversity of sediment-dwelling fauna generally remained lower than pre-cyclone levels.

Challenges and implications for fisheries management: A key challenge highlighted in the study was the absence of comprehensive pre-cyclone baseline data, complicating the assessment of the cyclone's impacts. The report recommends a precautionary approach to fisheries management and continuous monitoring to fully understand the long-term effects of such extreme weather events.

Impact on water quality: Dr Daniel Leduc, a benthic ecologist at NIWA, reported that of the 36 locations surveyed using an underwater camera, 11 showed evidence of sediment impact. "Analysis of satellite images suggest that the influence of Cyclone Gabrielle on water quality lasted approximately two to three months across the two regions," Dr Leduc was quoted as saying in a NIWA media release on Wednesday.

The research included extensive surveys conducted in June and October 2023 across Hawke’s Bay and Tairāwhiti, utilising satellite imagery, seafloor mapping, and underwater cameras to assess the cyclone's effects.

Further insights were gained through a seafloor model adapted by NIWA, which incorporated data on pre-cyclone bottom trawling, sedimentation, and biological characteristics of seafloor organisms.

Dr Leduc said, "the model suggested that habitat-forming organisms have been impacted by pre-cyclone fishing and sedimentation, and only limited additional declines in habitat-forming organisms, such as sponges, were predicted from the cyclone."

Future directions and management strategies: The NIWA report advocates for the use of sediment transport modelling as a valuable tool for identifying areas at highest risk from future sedimentation events. It also calls for integrated management strategies that address both immediate recovery and long-term environmental resilience.

Fisheries New Zealand intends to incorporate the findings from this NIWA study into updated management strategies and policies to enhance marine biodiversity protection and ensure the sustainability of the region's fisheries, in light of the increasing frequency and intensity of extreme weather events due to climate change.