Citation
Summary
The flatfish population in FLA 2 was last characterised using data up to the 2016 fishing year. Since then, the annual Total Allowable Commercial Catch (TACC) was reduced from 750 t to 150 t and annual aggregate flatfish catches dropped from 150 t to 250 t to near or below 50 t. In 2016, a bottom trawl (BT) target flatfish (FLA) catch-per-unit-effort (CPUE) series for combined FLA species in Hawke Bay was adopted as the abundance monitoring series. However, recent catch and effort data indicated that this series was no longer usable because only a single vessel participated in this fishery in 2023–24. A full review of the FLA 2 fishery was commissioned by Fisheries New Zealand for 2025, based on data up to the end of the 2023–24 fishing year, in order to update the understanding of this Quota Management Area (QMA).
This document provides a full characterisation of the FLA 2 commercial fishery on both sides of the North Island, including the spatial distribution of the catch and effort associated with the capture of FLA and an evaluation of the species composition of the catch, taking account of the September 2021 regulatory change that ensured full reporting of the catch by species. The historical species composition of the FLA 2 catch was inferred from the reporting practises of a subset of individual fishers who reported their catch as disaggregated species.
The Inshore Working Group (INSWG) agreed to use a CPUE series which included FLA bycatch in the BT target red gurnard (GUR) fishery, in addition to the target FLA fishery, because the target FLA CPUE series had been compromised through the loss of effort. Furthermore, the INSWG agreed to move from a daily BT series beginning in 1990 to a tow-by-tow, event-based, series beginning in 2007–08 because the shorter series included more complete species catch reporting as well as depth information associated with each event which could be used as an explanatory covariate. Three event-based series were accepted by the INSWG for monitoring FLA 2: combined FLA, NZ sole (ESO), and sand flounder (SFL). Two other species-specific series were not accepted because the data were too sparse for the series to be reliable monitoring tools: lemon sole (LSO), and yellow belly flounder (YBF).
Five near shore water quality series (dissolved oxygen mg-1, nitrogen gm-3, suspended solids gm-3, total phosperous gm-3, and water temperature deg C), monitored from 16 Hawke Bay stations over the period 2005 to early 2025, were matched with the CPUE series developed from this project. Not all stations were monitored over this period, with the most comprehensive coverage beginning in 2013. No significant correlations were found between the accepted FLA 2 CPUE series and any of the five water quality series.
A range of CPUE series were investigated as sensitivity analyses. These included daily resolution models extending back to 1990 with both FLA and FLA/GUR targeting, models that implemented the stepwise inclusion of covariates instead of the full suite of covariates, and series which split the effort of long-term participating vessels in order to test for learning over time. In addition, two trial CPUE series directed at the LSO and SFL fishing in the South Taranaki Bight section of FLA 2 were unsuccessfully attempted.
The three CPUE series accepted by the INSWG for FLA 2 abundance monitoring were evaluated against agreed BMSY-compatible proxies (FLA 2: geometric mean CPUE from 2007–08 to 2023–24; ESO 2: geometric mean CPUE from 2014–15 to 2023–24; SFL 2: geometric mean CPUE from 2011–12 to 2017–18). All three series were evaluated to be ‘About as Likely as Not (40–60%) to be at or above the target’, ‘Unlikely (<40%) to be below the Soft Limit’ and ‘Very Unlikely (<10%) to be below the Hard Limit’. Only the combined species FLA 2 series was evaluated against the overfishing target (at ‘Very Unlikely (<10%) to be Overfished’) because the historical species-specific catches are unknown.
This analysis of species composition was extended to the other NZ FLA QMAs in order to contrast with the FLA 2 results and to provide a baseline for these QMAs. Flatfish catches have reduced in all areas, although the FLA 1 catch has been stable for the last decade.
The FLA 1 fishery is dominated by yellow-bellied flounder, with a minor catch of sand flounder. Other species were reported historically, but are less apparent in the full catch reporting since 2021. New Zealand sole and sand flounder are the main species caught in FLA 2, although all flatfish species are reported to some extent. The proportion of lemon sole in the FLA 2 catch is related to the depths at which the gurnard target fishery operates in Hawke Bay. Lemon sole is the main species caught in FLA 3, with New Zealand sole and sand flounder also important and all species represented in the catch. In FLA 7, sand flounder and New Zealand sole appeared to dominate the FLA 7 catch historically, but the current fishery includes a mix of sand flounder, yellow-bellied flounder, lemon sole, and New Zealand sole, with turbot and brill also caught.
Greenback flounder was recorded in both the shallow flatfish fisheries, and in deepwater fisheries around the Auckland Islands, highlighting the possibility that it may comprise two similar species that are yet to be described separately.