PRO24-0021

This project used simulation modelling to explore potential bias in snapper SNA 8 stock assessments when there has been a change in stock productivity (i.e., regime-shift), as may be expected under climate change.

Three SNA 8 stock productivity-change scenarios were investigated: the first assumed an upward shift in productivity after 2000; the second assumed a downward productivity shift after 2000; the third had no productivity shift.

Various SNA 8 stock assessment models were run under these productivity shift scenarios including one that explicitly allowed for a post-2000 productivity shift. Assessment bias was investigated specific to two important management metrics: current-stock-biomass; current-stock-status (being the ratio of current-stock-biomass to stock virgin (unexploited) biomass).

All assessment models produced unbiased estimates of current-stock-biomass under the no-regime-shift scenario. Only the post-2000 productivity shift model produced unbiased current-stock-biomass estimates under increasing and decreasing productivity scenarios.

All model current-stock-status estimates were biased under increasing and decreasing productivity scenarios. Although the post-2000 productivity shift model current-stock-status estimates were markedly less biased that those of the other models. An important finding from the study was all models were substantively less biased in their estimates of current-stock-biomass than current-stock-status.

An important conclusion from the simulation work was that we should not be using model predicted stock-status ratios as stock assessment measures when it is suspected that stock productivity is likely to have changed. Instead, we should be placing more ‘faith’ in assessment model predictions of current-stock-biomass and therefore be measuring sustainability solely against these estimates.

The red rock lobster supports the most valuable inshore commercial fishery in New Zealand.

This fishery has been managed with catch quotas in nine Quota Management Areas (QMAs), which are usually treated as independent populations or stocks.

To estimate those quotas, a stock assessment is done for each QMA approximately every five years. These stock assessments include a review of the previous stock assessments and data inputs, the addition of new data, data processing, and development of a new stock assessment model.

This document describes the development of a new stock assessment model for the CRA 6 stock (the Chatham Islands).

The stock assessment estimated that since 1995, the stock size has steadily increased and is projected to increase over the next five years assuming current catches and recent recruitment patterns.

The 2016 Kaikōura earthquake caused significant coastal uplift resulting in high mortality of marine life, including pāua.

The pāua fishery is of high importance to customary, recreational, and commercial fishers in the region.

We undertook dive surveys to measure the recovery of the pāua populations on the affected coastline and have continued surveys since the fishery re-opening in 2021.

This report provides an update of survey results that have now been undertaken annually over 6 years.

Surveys have shown a steady increase of pāua abundance across the fishery and an increasing abundance of smaller pāua suggesting successful post-earthquake recruitment (appearance of juveniles in the population).

Data and outcomes from these surveys were used to inform the decision to re-open the fishery in 2021 and are now critical in informing future management decisions for the Kaikōura pāua fishery.

This report estimates the total recreational catch of southern bluefin tuna in New Zealand for the 2022–23 fishing year.

Tuna numbers and weights are collected using a monthly telephone survey of South Island fishers and a boat ramp survey at Waihau Bay in the eastern Bay of Plenty where most of these fish are landed.

Catch records from fishing clubs, online reporting, and recreational charter boats are also used.

In 2022–23, the Total Allowable Catch of New Zealand southern blue tuna was 1102 tonnes. The Commission for the Conservation of Southern Bluefin Tuna requires member countries to report their total catch.

Overall the number of southern bluefin tuna caught in the rereational fishery was about 1500, which is more than in previous years, but the average weight was lower.

The total landed weight for the recreational fishery was estimated to be between 65 and 73 tonnes with a mid-point of 69.3 tonnes.

The global population of southern bluefin tuna is increasing under the current management system and catch rates in the New Zealand commercial and recreational fishery are also likely to increase in future.

Most fishing methods catch target and non-target (unwanted) species, and unwanted catch may be returned to the sea in some cases.
Fishers and observers record catches of target and non-target species, and the amount of catch returned to the sea (discards).

Total non-target catch and discards for key species and species groups reported in the hoki, hake, ling, silver warehou, and white warehou (HHLSW) fishery from fishing years 2003 to 2022 were estimated with a statistical model.

Hoki and other target species make up most of the catch in this fishery, and key non-target species inluded javenlinfish, rattails, and sharks.
Gemfish showed a significant increasing trend in the amount of non-target catch reported, and sharks and slickheads showed significant decreasing trends.

The amount of catch that is discarded compared with the target catch is lower for this combined fishery than for other fisheries that are monitored.

Monitoring levels of catch and discards is important for understanding the impact of fishing on the environment.