Download FAR 2026/24 Updated harvest control rule for SBW 6B to allow for partial uptake of catch allowance

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 be greater than the initial TAC depending on the proportion of TAC taken in the first gap year and proportion of first gap year catch taken in the second gap year.
• For a three-year gap one combination of proportion of TAC taken in the first gap year and proportion of first gap year catch taken in the second gap year corresponding to the most recent set TAC and subsequent recorded landings was investigated. ‘Safe’ catches in the fourth year could be greater than the initial TAC depending on the proportion of second gap year catch taken in the third gap year.
These results are dependent on the life history and other modelling assumptions that were made for the stock.