Increasingly frequent and intense extreme weather events such as Cyclone Gabrielle are likely to impact seafloor marine ecosystems by accelerating soil erosion and sediment transport to the ocean by rivers.

The objective of this project was to understand sediment impacts from the February 2023 Cyclone Gabrielle event on marine environments of the Hawke’s Bay and Gisborne regions to enable rapid fisheries management decisions.

We conducted two vessel surveys in June and October 2023 focusing on offshore seabed environments deeper than 15 metres. As part of these surveys we mapped selected areas of the seafloor, surveyed life on the seabed using a towed underwater camera, and obtained sediment core samples.

An ocean current and sediment transport model was designed and implemented to investigate the transport and deposition of sediments after Cyclone Gabrielle. Concentrations of suspended sediments and other parameters in the surface ocean along the east coast of the North Island were estimated from satellite images. This satellite information was used to inform the sediment transport model and to characterise the spatial extent and longevity of the offshore sediment plumes generated by Cyclone Gabrielle. A Seafloor model was used to explore impacts and recovery of seafloor ecosystems following the cyclone.

The analysis of satellite images suggest that the influence of Cyclone Gabrielle lasted approximately two to three months across the Hawke’s Bay and Gisborne coastal marine areas, with surface ocean parameters largely returning to normal by May. The concentrations of suspended sediment at the ocean surface in February were significantly elevated, but they did not exceed values typical of winter months.
Seabed mapping revealed areas of significant sediment erosion, and deposition up to about one metre in thickness, at Pania Reef, Tangoio Reef and Clive outfall area in Hawke Bay. Elsewhere, sediment core observations suggested the presence of fresh muddy deposits of up to about 15 centimetres. Swell waves were resuspending muddy sediments at shallow locations for several months after the cyclone, as was evident by the low underwater visibility during camera deployments.

The abundance and diversity of the sediment fauna sampled in Hawke’s Bay and Gisborne before (2010) and after Cyclone Gabrielle (June and October 2023) tended to increase away from the shore and into deeper waters. Sediment fauna were less abundant in June 2023 when compared with 2010, but appeared to be recovering by October 2023.

Seafloor animal and plant communities are highly likely to have been impacted by sediments at 11 of the 36 locations we surveyed using the towed underwater camera, as assessed by observations including (1) fresh mud layer on the seafloor, (2) animal/plant life in poor condition, and/or (3) absence of seaweed at shallow depths. However, for most of these locations a direct link to Cyclone Gabrielle cannot be demonstrated because no information on the distribution of seafloor organisms is available from before the cyclone. The likely exception is Wairoa Hard in Hawke Bay, where available information shows that kelp and sponges were present before the cyclone but were almost completely or completely absent after the cyclone. Whether this loss of habitat has led to reductions in associated fish populations is unclear.

Although limited by the availability of data, the ocean current and sediment transport model produced realistic predictions of suspended sediment concentrations and deposition at the seafloor. In the days following the cyclone, sedimentation in Hawke Bay was predicted to occur mainly close to shore in the western and central parts of the bay. In the Gisborne region, there was deposition of up to about 10 centimetres of sediments offshore of Poverty Bay and along a narrow band of the coast to the north near Tokomaru and Tolaga bays. These model predictions are broadly consistent with observations from the sediment core samples.

The Seafloor model showed small declines in structure-forming organisms such as sponges for Hawke’s Bay following Cyclone Gabrielle. These declines were not substantial, most likely because the region is already impacted by decades of fishing and increased sedimentation. The Seafloor model predicted weaker cyclone impacts for Gisborne than Hawke’s Bay and indicated that continued trawling may slow down recovery of seafloor communities following extreme weather events.

The lack of pre-cyclone information was a major obstacle in assessing the potential impacts of the cyclone on seabed ecosystems. Information collected as part of this project now form a valuable baseline that will inform future impact assessments in the region. Another limitation is the inability to use towed cameras to survey inshore habitats for extended periods because of poor underwater visibility. A precautionary approach could be warranted in the period following an extreme weather event until key habitats and ecosystems can be surveyed, and fish stocks and catch levels should be carefully monitored in the years following the event.

Sediment transport modelling is a promising tool for rapidly identifying areas most at risk from sedimentation following extreme weather events. However targeted sampling of sediment and water parameters under normal and flood conditions would help improve the accuracy and reliability of model predictions. The Seafloor model could be used to explore how spatial changes in fishing effort could enhance recovery following extreme weather events and could be improved through better information on the distribution of seafloor sediment and reefs and their associated animal and plant communities, particularly in the Gisborne region.

The impact of extreme weather events is made worse by decades of increased sedimentation in New Zealand’s marine environments. Addressing the long-term issue of sedimentation in marine ecosystems and the impacts of extreme weather events will require addressing the factors that have made New Zealand’s catchments more prone to erosion.

Limited information is available on the understanding and preferences of the young, old, pregnant, and immunocompromised consumers on food safety matters. As such the outcomes of this report will be used to inform NZFS risk management/risk communication activities i.e., the development and implementation of strategies/food safety messaging/campaigns used to engage with YOPI.

New Zealand’s Hector’s dolphins are an endangered species. A key threat to their survival is entanglement in fishing gear, including trawl nets. In this study, we report on a field trial where underwater microphones (hydrophones) were fitted to trawling equipment and the echolocation clicks naturally produced by Hector’s dolphins were localised to determine how the dolphins interacted with the trawling equipment as it moved through the water. The hydrophones were protected within custom-built cages to withstand the physical stress associated with being attached to fishing equipment that is dragged along the seabed. The field trial was conducted off the coast of Timaru, New Zealand, in September and October 2022. While the hydrophones recorded dolphin sound underwater, a Fisheries New Zealand observer on the boat also looked out for dolphins.

The protective cages around the hydrophones proved effective and we were able to successfully localise dolphins. Dolphins were localised moving towards the mouth of the fishing net from various approach angles, and, on several occasions, we were able to successfully distinguish multiple dolphins each moving along different paths. Even though we only analysed a subset of the acoustic data from each trawl, dolphin clicks were detected acoustically during trawls on more occasions than the observer on the fishing boat was able to see dolphins. Unfortunately silt from the seabed entered some of the connections between the hydrophones and the acoustic recorder, which resulted in corrupted data on some days, but overall the field trial was successful.

This study showed that listening for the presence of dolphins can be more effective than looking for dolphins from a boat. We suggest that a combination of listening and looking for dolphins would be the most effective way to detect dolphins that might be near the fishing net. In the long term, the listening system described here could be developed into a real-time warning system that alerts the fishing vessel master when dolphins are close to the fishing net. If the vessel master is aware of the dolphins, they could avoid activities that result in high-risk of entanglement, such as sharp turns or drawing in the net at the end of the trawl. Dolphin detection could also help with targeted use of devices that encourage the dolphins to move away from the high-risk areas—such devices emit noise and should be used as little as possible to minimise noise pollution and disturbance to the dolphins.

The study investigates cryptic mortality (i.e., deaths that are not observed) of seabirds in New Zealand’s trawl fisheries, separately for net captures and warp cable strikes. For net capture-related mortality, the results suggest that, on average, mortality was 2.5 times higher than when only based on observed captures. For warp strikes, estimates varied based on data sources, highlighting the need for tailored data collection due to uncertainties and sparseness in the current dataset.

The Spatially Explicit Fisheries Risk Assessment framework has recently been updated and applied to assess the fisheries risk to seabird populations within the New Zealand EEZ. In the current report, the approach is applied to seabirds globally in the southern hemisphere. Catchabilities were estimated from New Zealand captures. Then global fishing effort and species distributions were collated and used to assess the risk to seabirds from predicted fisheries captures throughout their range.

A novel spatial risk assessment framework is proposed, based on the Spatially Explicit Fisheries Risk Assessment (SEFRA) and the Sustainability Assessment for Fishing Effects (SAFE). Risk is the probability that exploitation exceeds the Impact Sustainability Threshold (IST). Exploitation is estimated from the catchability and effort, using prior information on either the catchability or the population size. It is applied to shark and turtle species with different data characteristics.

This report provides a comprehensive overview of fishery data inputs for assessment of the risk of New Zealand commercial fisheries to New Zealand seabird populations. The risk assessment uses the Spatially Explicit Fisheries Risk Assessment (SEFRA) framework, which requires spatially resolved fishing effort and capture data. These data inputs were extracted from the Protected Species Capture database (version 6; up to and including the 2019/20 fishing year) and prepared for analysis.

This report details an implementation of the Spatially Explicit Fisheries Risk Assessment (SEFRA) framework to seabirds in the New Zealand Exclusive Economic Zone, attempting to quantify the impact of New Zealand commercial fisheries on New Zealand populations of seventy-one seabird species. As part of the project both the biological and fishery input data have been updated, as well as the structure of the model itself.