A review is provided of the available literature on ling, primarily to provide synopses on the biology and life history of the species from New Zealand and elsewhere, but also to describe the history and development of the New Zealand fisheries for ling and summarise the assessment and management of ling in New Zealand waters.

Catch and effort data from 1 October 1989 to 30 September 2018 (1989–90 to 2017–18 fishing years) for blue cod (Parapercis colias) in BCO 4 (Chatham Rise) was summarised and an index of biomass using standardised catch per unit effort (CPUE) estimated. The standardised CPUE series was based on positive catch record data from Statistical Areas 049, 050, 051, or 052 and because of significant fishing fleet changes in the 1990s only data from the 1997–98 fishing year onward were considered.

Catch and effort data from 1 October 1989 to 30 September 2018 (1989–90 to 2017–18 fishing years) for blue cod (Parapercis colias) in stock area BCO 3 (east coast South Island of New Zealand) was summarised and an index of biomass using standardised catch per unit effort (CPUE) estimated. The standardised CPUE series was based on positive catch record data from Statistical Areas 024 and 026 because of few catch records from the cod potting fishing method from other statistical areas.

Random age frequency sampling in 2019–20 gave catch-at-age estimates for SNA 1 longline and SNA 2 North trawl fisheries and a length frequency and age-length key approach allowed estimates of catch-at-length and -age for SNA 1 catches. Mostly, target sample sizes for numbers of landings were achieved and spatio-temporal comparisons revealed good sample representativeness. Catch-at-age distributions remain relatively broad with good representation across all recruited age classes up to 20 years.

A bottom trawl survey of the east coast South Island (ECSI) at 10–400 m depths was carried out using R.V. Kaharoa (trip code KAH2104) from 28 April to 12 June 2021. The core (30–400 m) survey was the thirteenth in the winter ECSI inshore time series (1991–1994, 1996, 2007–2009, 2012, 2014, 2016, 2018, and 2021). Four shallow strata (10–30 m), included in 2007, 2012, 2014, 2016, and 2018, were again surveyed in 2021 to monitor elephantfish and red gurnard over their full depth range.

A stock assessment was developed for GUR 7 integrating annual catches and Kaharoa WCSI trawl survey biomass indices and associated length and age compositions. The assessment model estimated that stock abundance increased considerably from 2010 following higher levels of recruitment during 2008–2019. For all model options, current (2021) stock status was estimated to be at about the equilibrium, unexploited biomass level (i.e., SB0). A range of potential management procedures were evaluated.

Recent trends in the GUR 3 fishery are summarised and standardised CPUE indices are derived for the main trawl fisheries. A stock assessment model was developed for GUR 3 incorporating trawl survey biomass indices and composition data and the CPUE indices. The assessment model estimated that stock abundance increased considerably from the late 2000s. Current (2021) stock status was estimated to be 51–68% SB0, well above the interim target biomass level.