Download FAR 2024/72 Characterisation, standardised CPUE, and assessment input data for scampi (Metanephrops challengeri) at the Auckland Islands (SCI 6A) for 1989–90 to 2022–23

Holmes, S.J.; McGregor, V.L. (2024). Characterisation, standardised CPUE, and assessment input data for scampi (Metanephrops challengeri) at the Auckland Islands (SCI 6A) for 1989–90 to 2022–23. New Zealand Fisheries Assessment Report 2024/72. 61 p.

Fisheries characterisations allow fisheries managers to understand if changes have taken place in the way a stock is being fished or if any other factors suggest a need for research or management attention.

A standardised Catch-Per-Unit-Effort (CPUE) index is a time series of catch per unit of fishing effort, modified or ‘standardised’ to account for changes in ‘fishing power’ or other factors; e.g., because of changes in fishing vessels, or the type of fishing gear deployed, or the seasonal timing of the fishery. Standardised CPUE can provide a proxy for the relative abundance of the stock, and this can be a valuable source of information for quantitative assessments that provide estimates of the stock’s size and status.

This report presents a characterisation for the scampi stock located near the Auckland Islands (SCI 6A) and a standardised CPUE index for that stock. It also details biological and other inputs necessary for a quantitative assessment of the stock.

The SCI 6A fishery developed in the early 1990s. Up to the early 2000s fishing was focused between January and May, but with some activity throughout the year. Since the introduction of scampi into the quota management system (QMS) in October 2004 the focus shifted more towards June to September with very little trawling between December and February, which is the period during which there is a higher incidence of post moult (soft shell) animals.

Catch data show most scampi live at depths between 350 m and 550 m. Most fishing activity is encompassed within the boundaries of a survey that uses trawl tows and photographs from a towed underwater sled to form fisheries independent indices of abundance.

Males and females are caught in different ratios depending on the time of year. Previous characterisations suggested the stock assessment model should account for this by splitting the fishing year into three time periods. Re-analysis of data presented here concluded only two time periods are necessary.

The commercial CPUE was standardised by the time of day of fishing (dawn, day, dusk, night), length of fishing tows, the type of gear deployed by a given vessel, and which of the time periods within a fishing year vessels operated, but changes to the unstandardised CPUE were small. CPUE appears cyclical over a time scale of six to ten years but with an underlying long-term decline to 2014 followed by a modest long-term increase thereafter.

Scampi assessments are length-based (because there is no reliable way to age scampi) and length distributions (proportions of animals at different lengths) are presented from sampling of commercial catches (‘observer sampling’), trawl survey data and photographic survey images. Length distributions from photographic survey images were not used in the latest assessment.