This SLMACC project followed on from a 25-year study of farm system impacts following land use and management change in the 260-hectare Mangaotama catchment farm (within the former Whatawhata Research Centre). The project has supported an improved understanding of the costs and benefits associated with land use and management change in pastoral hill country, occurring over time scales of multiple decades.

Mormede, S. (2024). Management strategy evaluation of New Zealand ling stocks. New Zealand Fisheries Assessment Report 2024/86. 33 p.

Ling (Genypterus blacodes) is an important commercial fish species in New Zealand middle depths waters and is caught mainly by bottom trawls, bottom longlines, and increasingly by potting.

This report summarises the management strategy evaluation of the three main ling stocks: the Chatham Rise (LIN 3&4), Sub-Antarctic (LIN 5&6 and LIN 6B) and the west coast of the South Island (LIN 7WC).

Results showed that the projected stock status was mostly affected by the assumptions of natural mortality and future recruitment. The different parameterisations of the harvest control rule had little effect. All simulations maintained biomass above the soft limit.

A potential target range was developed for ling, at 33–50% of initial biomass. Under such a target range, only a small subset of simulations would not achieve 50% probability of being above the lower end of target range.

Mormede, S. Dunn, A.; Webber, D. (2024). Longline observer data coverage in ling fisheries and their use in stock assessments. New Zealand Fisheries Assessment Report 2024/85. 30 p.

Ling (Genypterus blacodes) is an important commercial fish species in New Zealand middle depths waters and is caught mainly by bottom trawls, bottom longlines, and increasingly by potting.

On board cameras will be rolled out on all bottom longline vessels in December 2024, which is expected to lead to a reduction in the collection of biological samples that are used in ling stock assessments. This report investigates the observer coverage of the ling fisheries to date and the potential effect of the loss of longline observer data on the stock assessments.

Observer coverage has typically been lower for bottom longline vessels than trawl vessels, and less representative of the fishery. The bottom longline observer data was the most influential for the stock assessment of LIN 3&4 Removing bottom longline data in the assessment model of this stock resulted in a different estimate of biomass and status of the stock, highlighting the importance of these data to inform the stock assessment.

For the other ling stocks, the removal of the bottom longline data from the model did not result in a marked changed, possibly due to a lack of adequate observer coverage of these stocks. An increase in observer coverage may lead to a better-informed stock assessment and potentially different understanding of the status of these stocks.

The Deepwater Working Group recommended that observer coverage should be increased in bottom longline fisheries to inform the stock assessments better and that scientific research programmes using both observers and on-board cameras should be developed to leverage the most benefit from both systems.

The New Zealand Ministry of Fisheries (MFish) convened a review of New Zealand blue cod potting surveys on 16 and 17 April 2009. The review included: presentations by Expert Panel members about potting surveys; presentations by the scientists working on the New Zealand blue cod potting surveys; questions and discussion about the blue cod surveys; and conclusions from the Expert Panel. This report summarises the conclusions of the Expert Panel, relative to the Panel terms of reference.



This review occurred before the Fisheries Science Review series began, so it is being published retrospectively, to make the information (which is still relevant to blue cod science) more easily available.

This report summarises data collected in the third phase of the 15-year project to sample zooplankton and microplastic between New Zealand and the Ross Sea, Antarctica. We also analyse the full international dataset (1991–2023). Samples were collected in the project by towing the Continuous Plankton Recorder (CPR) behind the fishing vessel San Aotea II, during transits between Lyttelton and the Ross Sea.



Key findings:

1. The Ross Sea region is unusual: Consistent with previous work, this project has showed that zooplankton are more abundant in the Ross Sea sector than generally in the rest of the Southern Ocean.



2. Zooplankton are changing: Overall, we found a decreasing trend in total zooplankton abundance in the Ross Sea sector between 2008 and 2023. There are many different species of zooplankton and these did not all change in the same way over time, and some increased in abundance over the last 15 years.



3. Plastics are increasing: Our analysis has shown that average plastic abundance has increased 11-fold in the Ross Sea sector between 2009 and 2023, with 99% of the samples from the last 5 years containing at least one microplastic. Most of the plastics were microfibres.

Mormede, S.; Dunn, A.; Webber, D.N. (2024). The 2024 stock assessment of ling (Genypterus blacodes) in the Sub-Antarctic (LIN 5&6 and LIN 6B). New Zealand Fisheries Assessment Report 2024/84. 28 p.

Ling (Genypterus blacodes) is an important commercial fish species in New Zealand middle depths waters and is caught mainly by bottom trawls, bottom longlines, and increasingly by potting.

This report summarises the 2024 stock assessment of one of the five main ling stocks managed under the Quota Management System: the Sub-Antarctic ling stock, defined as LIN 5&6 and including LIN 6B for the first time.

A stock assessment model was carried out, informed by commercial catches, commercial age compositions, and information from the Sub-Antarctic Tangaroa trawl survey biomass series.

The initial spawning stock biomass (B0) for both the base case model was estimated to be about 204 630 t and stock status in 2024 was estimated at 66% B0.

Five-year projections were done using the base case model, assuming various future recruitment and annual catch options. Projected stock status in 2029 was expected to be above the target of 40% B0 in all instances, however the exploitation rate in LIN 5 was expected to exceed the target exploitation rate if the catch in LIN 5 was increased by more than 20%.

Mormede, S. Dunn, A.; Webber, D.N. (2024). Stock hypotheses for ling in the Sub-Antarctic (LIN 5&6 and LIN 6B). New Zealand Fisheries Assessment Report 2024/83. 13 p.

Ling (Genypterus blacodes) is an important commercial fish species in New Zealand middle depths waters and is caught mainly by bottom trawls, bottom longlines, and increasingly by potting.

This report investigates various stock hypotheses for in the Sub-Antarctic ling. Differences in growth suggested that LIN 3&4, LIN 5&6, and LIN 7WC were likely to be different stocks and that the current boundaries between those stocks were likely to be adequate. Catch rates, age structure, and growth data suggested that LIN 6B was unlikely to be part of LIN 3&4, with weak evidence that it was part of LIN 5&6.

Because of the paucity of data available to assess LIN 6B as a separate stock, and the similarities in the information between LIN 5&6 and LIN 6B, the Fisheries New Zealand Deepwater Working Group decided to include LIN 6B with LIN 5&6 as a single Sub-Antarctic ling stock (LIN 5&6 and LIN 6B) for the 2024 stock assessment of Sub-Antarctic ling.

Mormede, S.; Dunn, A.; Webber, D.N. (2024). Descriptive analysis of ling in the Sub-Antarctic (LIN 5&6 and LIN 6B) up to 2023 and inputs for the 2024 stock assessment. New Zealand Fisheries Assessment Report 2024/82. 94 p.

Ling (Genypterus blacodes) is an important commercial fish species in New Zealand middle depths waters and is caught mainly by bottom trawls, bottom longlines, and increasingly by potting.

This report summarises the 2024 characterisation of one of the five main ling stocks managed under the Quota Management System: Sub-Antarctic ling (LIN 5&6 and LIN 6B). The Total Allowable Commercial Catch (TACC) in LIN 5&6 is generally caught whilst that in LIN 6B has not been caught since 2005.

The bottom longline standardised catch per unit effort (CPUE) was updated for LIN 5&6 and for LIN 6B. Spatio-temporal CPUE indices were also developed and were in general agreement with the non-spatially explicit CPUE indices.

Length-weight relationships, von Bertalanffy growth curves, and maturity curves were updated for LIN 5&6. The maturity ogive for LIN 5&6 indicated some level of inter-annual variability. Only von Bertalanffy growth curves were updated for LIN 6B due to the paucity of data.

Inputs to the 2024 stock assessment of Sub-Antarctic ling are summarised.

Johnson, K.S.; Jordan, L.K.; McKenzie, J.R.; Bian, R.; Williams, J.R.; Underwood, M.J.; Morrison, M.A. (2024). Estimation of shellfish release survival from New Zealand commercial fisheries. New Zealand Fisheries Assessment Report 2024/81. 87 p.

This study estimated the survival of four shellfish species (scallops, queen scallops, paddle crabs, and sea cucumbers), when returned to the sea after being caught in New Zealand commercial fisheries. For species such as scallops with a minimum legal size (MLS), those below the MLS must be returned dead or alive, while for others such as sea cucumbers, their release is dependent not on size but on being alive and considered likely to survive (destination type code X). Estimates are based on previous local research, or studies with similar species overseas, along with responses to a questionnaire from fishers and fisheries managers with direct observations of immediate or at-release survival, and researchers with knowledge on post-release or longer-term survival. This information was analysed along with reported fishery data on how the shellfish returned to the sea were caught (such as dredge tow duration, speed, and catch size), to provide a range of likely survival estimates for each species and gear combination (differences between target and non-target fisheries are mainly due to differences in durations, speeds, catch sizes and/or seasons):

For New Zealand scallops, the survival estimates were “medium-high” (between 25% and 100% expected survival) for both box dredge and ring bag dredge.

For queen scallops, the survival estimate was “uncertain” (from 0–100% expected survival) for both target and non-target fisheries mainly due to the depth of this species and fishery compared to other scallop species that have been studied.

Paddle crabs below the minimum legal size had survival estimates that were “high” (over 50% expected survival) for potting and “low-medium” (0–75% expected survival) for trawl. For crabs released and considered likely to survive (destination type code X), the survival estimate from potting was also “high” and from trawling was “medium” (between 25% and 75% survival).

Sea cucumbers had a “medium-high” expected survival for the target trawl fishery, but “low-medium” for the non-target trawl fisheries and for dredge fisheries. For sea cucumbers released and considered likely to survive (destination type code X), survival estimates were “high” for the target trawl fishery, “medium-high” for the non-target trawl fisheries, and “medium” when caught by dredge.