Holdsworth, J.C. (2025). Recreational harvest of southern bluefin tuna in New Zealand, 2023–24. New Zealand Fisheries Assessment Report 2025/04. 22 p.

We estimate the annual recreational catch of southern bluefin tuna in New Zealand for the 2023–24 October fishing year. This information helps meet the obigation to report all of New Zealand’s catch of this species to the Commission for Conservation of Southern Bluefin Tuna each year.

Tuna numbers and weights are collected from a number of sources including:

sportfishing club weigh station records;
a monthly telephone survey of South Island fishers;
catch records from online reporting on the fishcatch.co.nz web page;
catch records from recreational charter boats;
records of recreational catch taken from commercial vessels for personal use; and
boat ramp interviews at Waihau Bay in the eastern Bay of Plenty (where most of the recreational catch is landed).
The estimated 2024 recreational harvest of southern bluefin tuna is 992 individual fish, which is fewer than in 2023 (1241 fish).

The estimated total landed weight for the recreational fishery is between 65 and 73 tonnes with a mid-point of 69.5 tonnes.

Dunn, A. (2025). Stock assessment of hake (Merluccius australis) off the West Coast South Island (HAK 7) for the 2023–24 fishing year. New Zealand Fisheries Assessment Report 2025/03. 68 p.

This report provides a stock assessment of the west coast South Island stock of hake (HAK 7 off the west coast of New Zealand) up to the end of the 2023–24 fishing year. The index of abundance provided to the model was the west coast South Island Tangaroa trawl survey series and this was combined with fishery and survey age composition data to model the population.

Initial spawning stock biomass (SSB) was estimated at 75 480 t (70 830–81 830) with current SSB 47% B0 (34–67% B0). The model was sensitive to assumptions about recent and future year class strengths. If we assume lower recruitment for years after 2017 (at the 2008–2017 level), the current SSB is estimated as 39% B0 (23–50% B0).

Holmes, S.J.; McGregor, V.L.; Underwood, M.J.; Wieczorek, A.M. (2025). Developments in scampi surveys: 2023–24. New Zealand Fisheries Assessment Report 2025/02. 19 p.

This report describes two separate pieces of work done in 2023–24 to improve the way scampi surveys are included in stock assessment models.

Scampi build and live in burrows made from the sediment in their environment. One of the ways scampi stocks have been assessed historically is with a series of photo surveys where the number of burrow entrances in a series of photos are counted by photo ‘readers’. There can be variability between readers in interpretation of bottom features as burrows. An individual reader’s interpretation can also ‘drift’ over time. A way to test for differences in interpretation between readers and for ‘reader drift’ was developed so that the burrow count indices could be properly calibrated.

In 2019, this calibration methodology was updated but when it was applied to later surveys there were large and unexpected adjustments which undermined confidence in the method. This report outlines the design for a simulation framework that could test whether the calibration method is performing as intended.

When an abundance index is used in a stock assessment model a catchability (labelled q) converts the numbers in the index to numbers in the population. These q values are estimated within the model, but the model uses ‘prior’ information about what values of q are considered reasonable. These prior distributions have historically been estimated by combining survey results with results from acoustic tag experiments. These have been used to estimate what proportion of the time scampi spend outside of their burrows and can therefore be caught by a trawl or seen in a photograph.

It has been found that the assessment results are sensitive to the specification of the q priors. A workshop was held to document how the q-priors had been calculated in the past and to agree on the best practise going forward. This report documents the results of this workshop.

Neubauer, P.; Kim, K.; Amar, T.; Prince, J. (2025). Stock assessment and spawning potential ratio-based management procedures for pāua (Haliotis iris) fisheries in PAU 3A. New Zealand Fisheries Assessment Report 2025/01. 139 p.

Stock assessments support the sustainable management of fisheries resources, such as pāua, throughout New Zealand. This study assessed pāua stocks in the area around Kaikōura, which was affected by the 2016 earthquake (now quota management area PAU 3A). The current project aimed to assess the status and management options for pāua stocks there by developing stock assessment models for pāua. The models were informed by fisheries, biological and survey data, and performed well based on data from the periods before and after the earthquake. Although there were some uncertainties about the representativeness of the survey data and about recreational take of pāua, the modelling estimated that the pāua stock in PAU 3A was at or above target levels in 2023. In addition, this study also evaluated management strategies for supporting sustainable pāua fisheries following the earthquake. This part of the study considered different limitations, known as harvest control rules, for pāua fisheries in this area. Different scenarios of limitations were assessed, associated with reproductive output of pāua. Based on the exploration of different strategies, the harvest control rules proposed here indicated that their implementation would maintain the PAU 3A fishery in a healthy state.