Introduction – May Plenary Report 2021 Volume 1

This report updates the stock assessment of Sub-Antarctic hake (HAK 1 south of 46° S) for the 2020–21 fishing year. The main index of abundance were the Sub-Antarctic trawl surveys. Initial spawning stock biomass was estimated as 59 000 t (95% credible intervals 43 220–93 600) with current status of 62% B0 (95% credible intervals 49–75% B0). Projections at the level of the current catch showed that the status would continue to remain at about the same level over the next five years.

This report summarises the Sub-Antarctic hake (HAK 1 south of 46° S) fishery with spatial structure of the stock, biological parameters, and standardised catch per unit effort (CPUE). The CPUE indices were similar for the tow-by-tow data and the daily summary data and showed a similar trend to the Sub-Antarctic trawl surveys. In general, the CPUE indices had declined over the period of fishing but had levelled off in recent years as the total catch declined.

This report presents population estimates for cockles Austrovenus stutchburyi and pipi Paphies australis at 8 sites in northern North Island for the 2020–21 fishing year. Also provided are sediment grain size and organic content data for Aotea Harbour, Kawakawa Bay (West), Ōhiwa Harbour, Okoromai Bay, Otūmoetai (Tauranga Harbour), Te Mata and Waipatukahu, Whangapoua Harbour, and Whangamatā Harbour.

Estimates of the fishing efficiency (Q) for 13 species for the R.V. Kaharoa South Island survey trawl gear were made by eliciting expert opinion. Estimates of areal availability taken from generalised additive model (GAM) analyses of the survey data were multiplied to the Q values to estimate overall catchability for seven key species. In five cases (elephant fish, red gurnard, snapper, stargazer, and tarakihi), catchability values were compared with estimates from integrated stock assessments.

Trends in the catch from the tarakihi fisheries within TAR 1, TAR 2, TAR 3, TAR 5, TAR 7, and TAR 8 are described for 1989/90–2019/20 fishing years. Standardised CPUE indices are derived for the main fisheries in each fishstock, including separate analyses for three areas of TAR 1 (Bay of Plenty, east Northland, and west coast North Island). Trends in the CPUE indices are compared amongst fisheries.

This project updated the fishery characterisation and CPUE standardisations for school shark in New Zealand, including size-frequency information. Trends in standardised CPUE differed across regions and sometimes across gears in the same region. New bottom trawl indices did not resolve the ongoing conflict in set-net and bottom-longline CPUE in SCH 2 & top of SCH 3. Trawl survey indices were accepted as index of abundance for SCH 7, SCH 8 & lower SCH 1W given declining set net effort.

A literature review revealed a wide variety of ocean acidification (OA) effects on fish. Tank experiments revealed both positive (growth and survival) and negative effects (metabolic performance and hearing) of OA and elevated temperature on snapper. A snapper population model that adjusted parameters to account for OA and elevated temperature suggested positive and negative outcomes were possible. Given this, further data collection and frequent monitoring to inform management would be prudent.

More than 170 groups nationwide are now receiving on-the-ground support to improve land management practices.

This literature review synthesizes the current state of knowledge of marine non-indigenous species treatments, to help address biosecurity risks evident in two focal areas of relevance to marine biosecurity management in New Zealand. These two areas are:
1. the proactive treatment of shellfish aquaculture stock to facilitate biosecure stock transfers; and,
2. the reactive treatment of non-indigenous marine species to enable eradication at the landscape-scale.
The review summarises ~280 published papers in the global literature, outlining a number of chemical, physical and biological treatment options that have been tested to varying degrees. Each identified treatment type was assessed for several attributes in the review, including application regimes, efficacy, safety, the ability to monitor during deployment, biosecurity risks, and the regulatory environment that may influence acceptance and use in New Zealand. A number of these treatments are believed to be effective at small scales. Scaling-up one, or a combination of these identified treatments is likely the most efficient development route. Co-development and collaboration with the aquaculture, marine construction and commercial diving industries is likely to be critical to developing safe, effective and efficient implementation-ready treatment protocols..