Photo surveys are used to estimate abundance of scampi in New Zealand and provide important information for stock assessments.

Readers identify features in the survey photos as burrows or scampi. A statistical model is applied to produce an estimate of abundance for each survey. The statistical model takes into account differences between readers’ interpretation of features (what looks like a burrow to one reader may not to another) and differences in interpreting features over time (e.g., a reader may become more skilled at interpreting features over time, or technology could improve).

This report provides a review of the statistical model applied to produce an estimate of abundance from scampi photo surveys. The review found no concerns with the model or how it is being applied. Two readers re-read images from recent survey years to test if the adjustment over time has been appropriate. The results of the re-reads supported the model results.

Further work is suggested, including contracting a specialist statistician to provide greater theoretical understanding of the model and assumptions.

The rock lobster fishery is one of New Zealand’s most valuable fisheries.

Understanding larval settlement processes can greatly assist the management of this fishery because they may explain changes in recruitment to the fishery (i.e., reaching legal size), which takes between four and eleven years. This report aims to determine trends in puerulus settlement at selected key sites around New Zealand.

Annual patterns of red rock lobster settlement are described for North Island and South Island coastal areas, based on monthly monitoring of puerulus (the post-larval stage of red rock lobster) settlement collectors.

The monitoring data for 2022–23 are described in this report and used to provide indices of puerulus settlement for 2022–23, and thus extend the time series used to identify annual trends of settlement (since 1979).

Puerulus settlement during the 2022–23 fishing year was above the long-term mean at Gisborne, Castlepoint, and Halfmoon Bay and below the long-term mean at Napier, Kaikōura, Moeraki, and Jackson Bay.

In New Zealand there are significant correlations between the level of settlement and fishery catch per unit effort for most fishery areas.

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.

Ling (Genypterus blacodes) is an important commercial fish species in New Zealand middle depths waters and is caught mainly by bottom trawls, bottom longlines, and increasingly by potting.

This report summarises the 2023 stock assessment of one of the five main ling stocks managed under the Quota Management System: the ling stock off the west coast of the South Island (LIN 7WC).

A stock assessment model was carried out, based on commercial catches, information from the west coast South Island Tangaroa trawl survey biomass series, the commercial longline standardised catch per unit effort (CPUE) from 1991, and the commercial trawl standardised CPUE from 1997.

The initial spawning stock biomass (B0) for both the base case model was estimated to be about 62 200 t and stock status in 2023 was estimated as 51% B0. An investigative model run provided a slightly lower initial biomass and stock status in 2023 of 52%.

Five-year projections were done using the base case model, resampling recruitment from the entire range of the model, and assuming future annual catch equal to the average catch in 2020–2022. Projected stock status in 2028 was expected to be 52% of B0.

The probability that the stock status in 2028 will be above 40% B0 was 97%, and that of being less than 20%, was zero. This assessment was used to inform Fisheries New Zealand’s management of this ling stock.

Catch-at-age data are important for the stock assessment of fish species because they provide information on the strength and progression of age classes in the stock, including juveniles and fish that are large enough to be taken by commercial fishers. These data include information on fish length and age (from otoliths—the ear bones of fish) collected at sea by observers from the commercial catch.

This report provides analyses of catch-at-age from the bottom trawl fisheries for barracouta (Thyrsites atun, BAR) in BAR 5 (Southland) and for gemfish (Rexea solandri, SKI) in SKI 3 (southeast coast) and SKI 7 (Challenger) for the 2021–22 fishing year. These results are the second of a three-year catch-at-age series for these two species.

Data for the 2021–22 season included few barracouta under 60 cm, indicating either less fishing on smaller (and younger) barracouta, or a poor year class should be expected. Most of the barracouta were aged 2–5 years.

Gemfish from SKI 3 in the 2021–22 fishing year showed a range of fish sizes, with most between 45 and 52 cm, which corresponded to age 2 fish, and also at sizes that corresponded to ages 4–6.

Gemfish from SKI 7 were less variable in length and included some fish under 50 cm, mainly females, which corresponded to ages 0–1. Most of the gemfish in SKI 7 around 50 cm in length corresponded to age 2; this was a strong cohort, particularly for males. Females were generally larger (and older) than males in the bottom trawl catch, with a strong mode at ages 5–8 for the females.

A stock assessment survey of Foveaux Strait oysters (OYU 5) in February 2023 found numbers of commercial-sized, recruit, pre-recruit oysters, and small oysters had decreased by between 44.8% and 52.3% from 2022 numbers. Winter-spring disease mortality is the most likely cause. These decreases cannot be fully explained by fishery and survey data. Summer mortality from Bonamia increased from 5% in 2022 to 9% in 2023. Mostly large oysters died; 70% of oysters are below recruit-size. Spat settlement was high.

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.

This report updates and summarises the observational and research data for southern blue whiting from 1990 to 2022. These data include the time series of relative abundance from acoustic surveys, trawl survey indices, and updated time series of length-at-age and catch-at-age from observer sampling of commercial catch.

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.