Holmes, S.J. (2026). Updated harvest control rule for SBW 6B to allow for partial uptake of catch allowance. New Zealand Fisheries Assessment Report 2026/24. 9 p.
 

Southern blue whiting (SBW) on the New Zealand Bounty Plateau (SBW 6B) is managed by using a harvest control rule (HCR) to set the Total Allowable Catch (TAC). The HCR as first developed depended on an industry acoustic spawning biomass survey conducted in the year before its use. It was later adapted to account for years with missing surveys (gap years). It was found, through simulation studies, that for each successive gap year the initial TAC should be reduced by a scalar, which was estimated to be between 0.87 and 0.83. The scalar reduced the catch to ensure that the stock remained above the limit reference point (20% of unfished spawning stock biomass) with an acceptable probability. The revised HCR assumed that the allowed TACs were fully caught, but this has not been the case in recent years. The current report investigated the effect of part utilised TACs. It found that:

• For a one-year gap there was a linear relationship between the proportion of TAC taken in the gap year and the level of ‘safe’ catch possible in the second year. This safe catch could be greater than the initial TAC set for the gap year if catch in the gap year had been less than 90% of the initial TAC.
• For a two-year gap ‘safe’ catches in the third year could

Using fisher-reported start and end points, and a method that assumes trawl paths follow straight lines between those points, the study analyses trends in different measures of seabed contact for these groupings. The measures include the area in square kilometres of the overall trawl footprints and aggregate (cumulative footprint) areas by year and all years combined, the number of tows, the number of cells contacted (a 5 km × 5 km grid overlaid on the fishable area), and the number of ‘new’ cells contacted each year that had previously not been contacted.

Key findings include:

• All Stocks (2008–2023): The area of seabed contacted each year declined over time, with the lowest footprint recorded in 2023. Each year, trawling activity affected between 1.7% and 2.3% of the total EEZ + TS seafloor, and between 5.0% and 6.8% of the fishable area (areas open to trawling down to 1600 m). The number of

• Ling is a commercially important fish species. An important ling fishery takes place on Chatham Rise.
• Fish and fisheries are affected by environmental conditions. Environmental conditions in Aotearoa New Zealand are affected by climate variability and change.
• We used information from drifting buoys, satellites and computer modelling to describe the oceanographic conditions experienced by ling on Chatham Rise over the last 40 years.
• Chatham Rise is an underwater feature that extends eastwards for about 800 km off the east coast of the South Island, with the Chatham Islands at the far end. The ocean is particularly productive here because it is where ocean currents meet, leading to good conditions for phytoplankton; the tiny plants living in the upper ocean. This in turn supports a rich food web, including ling and other deepwater fish.
• Environmental observations show that the oceans around New Zealand are getting warmer, and the pace of warming has accelerated over the last 20 years. Chatham Rise is warming particularly quickly, and the warming extends from the sea-surface to the seabed though warming at the seabed is slower than at the surface.

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).
• ISSN: 1179-5352;
  ISBN: 978-1-991407-58-0;
  AUTHOR: Holdsworth, J.C.;
  FAR: 2025/52;
  

Neubauer, P.; Kim, K.; Middleton, D.A.J.; Cook, D.; A’mar, T. (2025). Investigating length-based management procedures for Trachurus novaezelandiae in the Bay of Plenty purse-seine fishery. New Zealand Fisheries Assessment Report 2025/49. 78 p.

This study evaluated using fish length to adjust catch limits for a jack mackerel species in New Zealand waters, with a view to developing simple length metrics to help manage this species. The effectiveness of length-based management depended greatly on biological factors like recruitment, growth, and natural mortality. Current uncertainties about these factors make length-based rules less reliable than expected. Alternative approaches using age data might provide a better way to support sustainable management of this species.