Characterisation and CPUE analyses for the gemfish fishery in SKI 3 and SKI 7 to 2020

South Island gemfish (Rexea solandri, SKI), found in Quota Management Areas (QMAs) 3 and 7 (Figure 1), are considered to be a single stock. South Island gemfish were heavily fished, beginning in the late 1970s and extending into the early 1990s, with catch rates and catches rapidly diminishing from a peak in 1986 to low levels after 1991. This report presents detailed data from 1990 up to the end of the 2020 fishing year4 and characterises the fisheries which capture gemfish in SKI 3 and SKI 7, including gemfish landings by capture method, gemfish catch locations and depth range of capture, plus associated captured species.

This report presents detailed analyses of all available catch-effort data for SKI 3 and SKI 7 from 1990 up to the end of the 2020 fishing year, extending a preliminary catch-per-unit-effort (CPUE) analysis which included data to 2018. Three southern gemfish fisheries were identified: (1) SKI 7 target hoki; (2) SKI 3 Stewart-Snares shelf; (3) SKI 3 East coast South Island. Four CPUE series, based on different data sources (commercial tow-by-tow, daily processing, observer, and commercial daily “rollup”), were analysed for each fishery, except for the SKI 3 East coast South Island fishery where there were insufficient observer data to generate a series.

The Deepwater Working Group (DWWG) accepted that all eleven series indicated that there had been a considerable increase in apparent relative biomass in the late 2010s compared with the low levels of gemfish observed during the period 1990 to the mid-2010s. The DWWG preferred the daily processing series because these series would have been less affected by the limitations of the species reporting requirements of the TCEPR forms during the period of low abundance and that these series covered more years than the observer CPUE series. The DWWG also accepted the SKI 7 target hoki (Macruronus novaezelandiae, HOK) daily processing series as the primary abundance indicator for southern gemfish because it operates during the spawning period in the location where this stock is presumed to spawn. The SKI 3 Stewart-Snares shelf series was viewed as a corroborative series which operates in the feeding and migratory region for this stock. The DWWG noted that the gemfish index from the 2018 Tangaroa survey showed an increase that was consistent with the SKI 7 target HOK series. This observation corroborated the SKI 7 target HOK CPUE series, despite the short period covered by the west coast Sout