South Island recreational blue cod fisheries are monitored by Fisheries New Zealand using potting surveys to assess the status of the stocks. The results of the Foveaux Strait surveys are important inputs for full quantitative stock assessments conducted for BCO 5 every five years.

This report describes the results of the random-site blue cod (Parapercis colias) potting survey carried out in Foveaux Strait in February 2023—as well as for three previous surveys (2010, 2014, and 2018). Estimates are provided for population abundance, size structure from fish length, and age structure from otoliths (ear bones collected for ageing), as well as population sex ratio, total mortality, and fishing mortality.

The overall weighted mean length of blue cod in 2023 was 32.0 cm for males and 28.5 cm for females, and mean age was 5.9 years (1–11 years) for males and 6.2 years for females (1–16 years). There were no clear age class modes in 2023 and little evidence of spawning activity during the survey.

The scaled length frequency distributions and mean length of all blue cod were similar for all four surveys, although, in 2023, the proportion of small males was less than in previous years.

Survey abundance (total blue cod mean catch rate) from the four surveys significantly increased between 2010 and 2014, with no change in 2018, followed by a significant decline of 57% in 2023.

The proportion of pots with no catch was similar for the first three surveys (25 to 32%), but in 2023 this increased to 49%. There were no trends in sex ratio over the time series which was around 50% male.

The age structure was similar among the four surveys with most fish between 4 and 8 years of age and relatively few fish over 10 years, particularly males. The fishing pressure is concentrated on just a few older cohorts, some of which are poorly represented.

Relative to the target reference fishing mortality of F=0.15 for blue cod, the estimated mortality in 2023 was nearly seven times higher, indicating that overfishing is occurring. Fishing mortality was also considerably higher than the target for all three previous surveys.

The aim of this project is to provide a pathway that enables New Zealand to implement the 2013 WS

methodology for drained Organic Soils. The objectives were to:

1 review spatial data to inform the current and 1990 extent of Organic Soils, and review classification

approaches and their implications

2 review approaches to estimating current and 1990 activity data for Organic Soil areas, including

nutrient status, drainage depth, and land-use class

3 review IPCC emission factors and existing greenhouse gas measurement studies from Organic Soils

in New Zealand, and examine the ability to derive New Zealand / region-specific emission factors

based on these data

4 provide recommendations to implement the 2013 WS at a minimum level and make recommendations

for where future research should be prioritised to improve emission estimates for drained Organic

Soils in New Zealand on the basis of the highest sources of emissions and/or the highest sources of

uncertainty

This Sustainable Land Management and Climate Change (SLMACC) project “Quantifying climate change adaptation plans” uses kiwifruit and avocado as exemplars of high-value crops. It aims to predict the performance of horticultural crops under climate change, to quantify growers’ exposure to climate change, and to model how this exposure is affected by adaptations designed to ameliorate climate impacts.

The impact of floods on the primary sector was first assessed nationally and then for the Awanui River Catchment in Northland. The analyses focused on the impacts of flooding on the primary sector, including changes in land uses as an adaption response to floods with climate change and subsequent changes in economic and environmental indicators. The specific objectives of the analysis are to:

1 quantify New Zealand’s primary sector exposure to flood hazards.

2 quantify the primary sector’s exposure and financial losses from floods in one catchment – the Awanui catchment.

3 analyse the impacts of flooding on land-use change and economic and environmental indicators.

4 evaluate economic and social welfare changes from floods-induced land-use change.

This study explores the impact of climate change on biological control of the Woolly apple aphid (Eriosoma lanigerum, WAA) by its parasitoid Aphelinus mali. Changes in temperature affect the survival and development of A. mali, potentially influencing its effectiveness in controlling WAA populations. The study shows that temperature variations impact the survival and development of A. mali. While warmer conditions enhance parasitism rates, factors like extreme heat events and host population changes may counteract the positive effects. Highlighting the complex dynamics of climate change on insect pest control and emphasizing the need for a nuanced understanding of how climate change affects pest management strategies.

Faecal source tracking, water management, Norovirus, shellfish

Shellfish may become contaminated by potential human pathogens when they come into contact with water containing human sewage or agricultural runoff. MPI contracted ESR to identify and evaluate available chemical and microbial source tracking methods and technologies that could be used as indicators of human or animal faecal contamination, particularly in NZ shellfish growing areas, thereby offering opportunity to better manage these areas minimising commercial and public health impacts.

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.

Sea urchin barrens are sea urchin dominated areas of rocky reef that would normally support healthy kelp forest, but have little or no kelp due to overgrazing by sea urchins.

This review updates our understanding of sea urchin barrens in New Zealand and the role fishing plays in their establishment to date. It also identifies key work required to support management decisions, including collating data on the distribution of urchin barrens, reviewing information required to set catch limits for sea urchin predators, and developing regional management approaches.

We review published scientific literature on sea urchin barrens in New Zealand and the role of fishing in their development.

We also summarise results of a national workshop to support management of sea urchin barrens.

Research based on observations from marine protected areas suggests fishing of sea urchin predators is causing and/or maintaining sea urchin barrens in north-east New Zealand.

The extent of sea urchin barrens and contributing factors in other parts of New Zealand appear to vary, but there are few published studies on this.

Workshop discussions indicated an urgent need to develop a suite of management options to address sea urchin barrens at regional scales in collaboration with tangata whenua and stakeholders.