South, P.M.; Delorme, N.J.; Ragg, N.L.C.; Taylor, D.I. (2024). A quantitative assessment of mussel nursery site performance. New Zealand Aquatic Environment and Biodiversity Report No. 346. 10 p.
Individual batches of mussel spat were split among eight marine farms to assess whether any appear to be better for spat retention and growth.
By splitting single batches of spat we reduced some of variability in spat condition and seeding practices that can make it difficult to determine good farms for growing spat.
We found that one farm was better for spat retention than all the others and one farm produced bigger spat.
Prior to the spat deployment, each of the eight farms had been graded by mussel farmers as being good, average or poor for spat retention. We found that spat on farms that were predicted to be poor for their retention and growth performed similarly to the good sites. This suggests that it might be possible to grow spat successfully at previously overlooked farms. Further deployments of spat will be used to verify these findings.
Finucci, B.; Dunn, M. R. (2024). Post-release survival for leatherback turtles caught in New Zealand surface longline fisheries. New Zealand Aquatic Environment and Biodiversity Report No. 345. 36 p.
The Critically Endangered and declining population status of the Western Pacific leatherback turtle population makes it important to quantify the post-release survival for leatherback turtles caught in surface longline fisheries in New Zealand.
This report summarises information on at-vessel and post-release survival for leatherbacks globally.
Two workshops were conducted during this project, to better understand the New Zealand surface longline fishery and to agree to a scoring scheme for estimating leatherback post-release mortality.
Post-release survival for leatherbacks caught in the New Zealand surface longline fishing fleet was estimated to be about 78%. This estimate was based upon 23 interactions.
The objective was to compare leaching losses of N and P from diverse pastures, consisting of 5-8 species, with losses from traditional ryegrass-white clover at two sites, near Lincoln, Canterbury and Tihoi, Waikato. Large-scale lysimeters were employed to directly measure leaching for a range of management intensities and across different soil types over four years. The results did not show a consistent difference in leaching between the two pasture types. However, pasture establishment was variable across the sites, with high losses recorded during drainage events that occurred when pasture establishment was incomplete. These results suggest timing of management activities, such as cultivation and irrigation, is likely more important than pasture species composition for reducing leaching losses.
This project sought to provide new information on how catch crops could be established earlier, better managed and shown to reduce the risk of nitrogen leaching and runoff and provide production benefits. The research examined crop choice; sowing method, timing and rate; lysimeter measurements; modelling and farmer uptake of the results. An engaging and collaborative approach was taken throughout the project, from trial establishment on working farms to linking with other researchers and Overseer Ltd as findings emerged.
This project explored management options to maximise the ability of radiata pine to transfer nitrogen from nutrient-rich soils into tree biomass. The project collected data from 12 existing afforestation sites and 3 newly installed pastoral afforestation trials, enabling projections of nutrient movement and storage over the life of a rotation. These predictions demonstrated a substantial opportunity exists to rapidly reduce soil nitrogen loads to manageable levels, but the 3 new afforestation trials need to run another 4 to 5 years to provide sufficient evidence to enable confidence in wider adoption. The trial sites, on Pamu Farms properties, are a unique resource, and could be utilised for silvopastoral systems research on biostimulants, residue management and biofuel generation alongside pastoral farming.
McGregor, V.L.; Holmes, S.J. (2024). Assessment modelling of scampi (Metanephrops challengeri) at the Auckland Islands (SCI 6A) in 2024. New Zealand Fisheries Assessment Report 2024/76. 66 p.
Integrated stock assessments provide estimates of stock status based on all available data and information. Stock status is the current biomass of the stock as a percentage of the biomass before the stock was fished. This report presents an integrated stock assessment model for scampi in the Auckland Islands (SCI 6A) that was not accepted by the Fisheries New Zealand Deepwater Working Group for the assessment of this stock. It includes information on the biology of scampi and data from commercial fisheries and research surveys. The model used two annual time-steps to reflect changes in vulnerability of males and females as moulting occurs at different times. Key concerns with the model were on the input data and suggest more work is required to understand inconsistencies within and between the datasets.
Holmes, S.J.; McGregor, V.L. (2024). Characterisation, standardised CPUE, and assessment input data for scampi (Metanephrops challengeri) at the Auckland Islands (SCI 6A) for 1989–90 to 2022–23. New Zealand Fisheries Assessment Report 2024/72. 61 p.
Fisheries characterisations allow fisheries managers to understand if changes have taken place in the way a stock is being fished or if any other factors suggest a need for research or management attention.
A standardised Catch-Per-Unit-Effort (CPUE) index is a time series of catch per unit of fishing effort, modified or ‘standardised’ to account for changes in ‘fishing power’ or other factors; e.g., because of changes in fishing vessels, or the type of fishing gear deployed, or the seasonal timing of the fishery. Standardised CPUE can provide a proxy for the relative abundance of the stock, and this can be a valuable source of information for quantitative assessments that provide estimates of the stock’s size and status.
This report presents a characterisation for the scampi stock located near the Auckland Islands (SCI 6A) and a standardised CPUE index for that stock. It also details biological and other inputs necessary for a quantitative assessment of the stock.
The SCI 6A fishery developed in the early 1990s. Up to the early 2000s fishing was focused between January and May, but with some activity throughout the year. Since the introduction of scampi into the quota management system (QMS) in October 2004 the focus shifted more towards June to September with very little trawling between December and February, which is the period during which there is a higher incidence of post moult (soft shell) animals.
Catch data show most scampi live at depths between 350 m and 550 m. Most fishing activity is encompassed within the boundaries of a survey that uses trawl tows and photographs from a towed underwater sled to form fisheries independent indices of abundance.
Males and females are caught in different ratios depending on the time of year. Previous characterisations suggested the stock assessment model should account for this by splitting the fishing year into three time periods. Re-analysis of data presented here concluded only two time periods are necessary.
The commercial CPUE was standardised by the time of day of fishing (dawn, day, dusk, night), length of fishing tows, the type of gear deployed by a given vessel, and which of the time periods within a fishing year vessels operated, but changes to the unstandardised CPUE were small. CPUE appears cyclical over a time scale of six to ten years but with an underlying long-term decline to 2014 followed by a modest long-term increase thereafter.
Scampi assessments are length-based (because there is no reliable way to age scampi) and length distributions (proportions of animals at different lengths) are presented from sampling of commercial catches (‘observer sampling’), trawl survey data and photographic survey images. Length distributions from photographic survey images were not used in the latest assessment.