Fisheries reports and stock statistics

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.

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.

This report presents the results of the updated trawl footprint in New Zealand waters within the Exclusive Economic Zone in waters open to trawling to a maximum depth of 1600 metres (fishable area).
Results are presented for the 1989–90 to 2021–22 fishing years for deepwater fisheries, and for the 2007–08 to 2021–22 fishing years for inshore fisheries, and combined inshore and deepwater (‘All stocks’) fisheries.
Statistics are presented on the measures of seabed contact for these groupings and include the area in square kilometres of the overall trawl footprints and aggregate (cumulative footprint) areas by year and all years combined. Other measures of contact also presented include the number of tows, the number of cells contacted (a 5 × 5 kilometre grid overlaid on the fishable area), and the number of ‘new’ cells contacted each year that had previously not been contacted.
This study also considered the above measures of contact when including midwater trawl used within five metres of the seabed and within ten metres of the sea bed. Methods were also developed to refine the placement of bottom-contacting trawl effort on underwater topographic features.
Results show that overall measures of contact have decreased in recent years for deepwater, inshore, and All stocks fisheries. Measures of contact increase little when including midwater trawl used within five metres and ten metres of the seabed. The development of methods to refine mapping of trawl effort to underwater topographic features shows promise but would benefit from external validation, perhaps through comparison with data held by the fishing industry.

Cyclone Gabrielle (13–14 February 2023) caused widespread severe damage in the Te Matau-a-Māui/Hawke’s Bay and Tairāwhiti/Gisborne regions. Soil erosion caused by intense rainfall deposited sediment and woody debris in river valleys and in the sea. This project measured the proportional contributions of major rivers to the cyclone sediment deposits in the sea, and describes the physical characteristics of these deposits.

River sources accounted for more than 98% of these mud-rich deposits. In northern Tairāwhiti, deposits were dominated by the Waiapu River. In Hawke’s Bay and Poverty Bay, cyclone sediment deposits mainly originated from the Mohaka and Wairoa-Nuhaka Rivers. These findings demonstrate that sediment plumes from Hawke’s Bay rivers were transported north along the coast, all the way around around Mahia Peninsula and deposited in Poverty Bay. The overwhelmingly land-derived origin of the marine deposits highlights the vulnerability of the East Coast to soil erosion and marine sedimentation.

Scallops (Pecten novaezelandiae) play an important role in Aotearoa-New Zealand’s coastal marine ecosystem, and they are highly valued as a taonga and fishery species. However, large declines in scallop numbers have occurred, and the main scallop fisheries are currently closed.

In some areas, seabed habitats appear degraded and no longer suitable for scallops, and poor habitat quality is thought to be the main barrier preventing scallop recovery.

In this study, we reviewed knowledge of scallop habitat preferences, and conducted a field experiment to investigate scallop survival and growth in relation to habitat characteristics. The field experiment was conducted in 2018 at a range of sites in Golden Bay and Tasman Bay, at the north of the South Island. Small juvenile scallops (spat) were marked and released at the sites in May, and the sites were surveyed by divers in June and December. Scallop spat survival was very low in muddy/simple habitats, and much higher in sandy/complex habitats.

The study suggests scallop population recovery may only be expected to occur in areas with suitable habitat.

We looked at the population DNA structure of common dolphins in New Zealand and how connected they are with the common dolphin populations in Eastern Australia and Tasmania.
We also used this information to estimate the effective population sizes.

DNA was extracted from New Zealand and Eastern Australian common dolphin samples collected from stranded, by-caught, and biopsied free-ranging individuals.

Three different populations were identified: 1) east coast of Australia; 2) west coast of New Zealand/Tasmania; and 3) east coast of New Zealand. There was migration from the east coast of New Zealand population into the west coast of New Zealand/Tasmanian population, and low migration into/from the east coast of Australia population.

Estimates of effective population size were higher for the east coast of New Zealand population, compared with the west coast of New Zealand/Tasmanian population.

The ‘petrel project’ continued the use of on-board cameras to monitor seabird captures in the small-vessel bottom longline fishery off the north-east of New Zealand. Results demonstrated the value of the video observation data in providing data that were representative of the fishery, and the importance of assessing the variation between reviewers in their ability to make observations from the footage. Footage was reviewed to May 2022 and, for the first time, included reviewing footage from the winter months (June– October) in addition to the November–May period when black petrels and flesh-footed shearwaters are breeding in the area. Models using the video observation data estimated 40 black petrel captures, and 159 flesh-footed shearwater captures, in all bottom longline fishing in Fisheries Management Area 1 during the 2021–22 fishing year. The estimated captures of black petrels were lower than previous estimates, which were based on observed data only, but estimated captures of flesh-footed shearwaters were similar. Additional blind reviews were carried out of footage where captures occurred to allow estimation of reviewer skill. Of the five reviewers involved in the project, two reviewers detected over 90% of the seabird captures, but one reviewer detected fewer than 50% of the captures.

Nga Hapu o Te Uru o Tainui Fisheries Forum raised concerns with Fisheries New Zealand over mass mortality of some shellfish, especially tītiko or pupu (mud snails), observed by iwi members around the margins of the Kawhia and Aotea Harbours, in northwestern New Zealand.
The mass mortality of the shellfish appeared to have coincided with the spraying of herbicide around the margins of the harbour to control an invasive marsh plant Spartina, raising the possibility of collateral effects from chemical contamination.
Surveys of shellfish size and abundance, as well as analyses for a wide range pesticide residues in samples from the two harbours could find no indication of possible effects due to chemical contamination.
Tītiko from these two harbours should be safe for human consumption based on the consistent absence of chemical pesticide residues of concern in the analyses of sediment and tītiko tissues.

Middleton, D.A.J.; Gibbs, N.; Tuck, I.D.; Tunley, K.L. (2024). A review of fishery classifications for
reporting of environmental and ecosystem considerations.
New Zealand Aquatic Environment and Biodiversity Report No. 338. 63 p.
The environmental and ecosystem information needs of fisheries managers and other stakeholders were
assessed through a workshop and survey. We concluded that reporting the environmental impacts of
fishing by fishery, rather than species, was the best approach.
Similar approaches to defining fisheries are used in New Zealand and internationally. However, when
projects do not use the same definition for a fishery this complicates compiling results at the fishery level.
A well-defined, and comprehensive, classification is recommended for future reporting. It should be
hierarchical, allowing groups to be merged or split as required.
Existing resources can be built upon to efficiently implement a new framework for annual, fishery-level
reporting.

Scallop populations have declined across Aotearoa New Zealand and have failed to recover even after fisheries closures. It has been suggested that seafloor habitat health, rather than the number of larval recruits arriving to the seafloor, is the critical factor impeding scallop recovery in formerly abundant beds. The aim of this research was to identify optimal habitat characteristics for scallops and to determine why sites that once supported scallops no longer do. We reviewed models and data on stressors to understand how multiple stressors may have degraded scallop habitats in the Marlborough Sounds. We used field surveys of 230 sites across Aotearoa New Zealand (Northland, Auckland, Coromandel Peninsula, and Marlborough Sounds) to assess seafloor environmental characteristics in relation to scallop abundance. Our reviews revealed how human activities both on land (land clearance and forestry) and in adjacent coastal zones (bottom contact fishing) have likely impacted scallops in the Marlborough Sounds, although a lack of information on stressors at the times and places of scallop population declines precluded a clear demonstration of cause and effect. Our field data highlighted relationships between scallops and their environment, including sets of conditions where scallop densities were at their maximum, enabling us to better define what constitutes ‘good’ scallop habitat. Without this understanding, scallop restoration efforts may be less successful.

The impacts of bottom trawling and dredging on seabed habitats and species is recognised as one of the top pressures on New Zealand’s marine ecosystems.

This report uses prioritisation software to explore spatial management options that can reduce the impacts of bottom trawling on seabed habitats and species.

The project focussed on protected species such as deep seas corals, and other rare, threatened, endemic or fragile species that are vulnerable to bottom trawling.

A diverse stakeholder group, including industry, environmental organisations, central government and regional government, attended five stakeholder workshops and informed the selection and parameterisation of hypothetical scenarios to reduce the impacts of bottom trawling.

More than 50 scenarios of different spatial management options were performed, showcasing how the software could be used to identify options that maximise benefits to benthic biodiversity and minimise costs to the fishing industry.

The analyses also assessed the current levels of protection provided by Benthic Protected Areas and seamount closures to protected seabed habitats and species.

MPI has responded to concerns raised by Te Tau Ihu Fisheries Forum about the possibility of ongoing environmental pollution impacts on kaimoana in the Waimea Estuary.
This research report was aimed at assessing the risks posed by past and present land-based chemical pollutants led by mātauranga Māori of kaimoana in in the estuary in combination with a review of western knowledge about the toxicology of synthetic chemical compounds.
Historically, the Waimea Estuary has been the receiving environment for a wide range of persistent pesticide chemicals, including DDT and its breakdown products (DDX), and also dieldrin and lindane, associated with the operation of the Fruitgrowers Chemical Company in Māpua from 1931 to 1988.
Samples of seafloor sediments, tītiko (mud-snails), tuangi (cockles), kūtai (mussels), and pātiki (flounder) were analysed for a wide range of heavy metals and organochlorine pesticides and residues (OCPs).
Results showed DDX levels in tītiko collected from closest to the former FCC site to be the highest, and at levels that are unsafe for human consumption, however, concentrations in tītiko further away had safe levels.
All tuangi, kūtai and pātiki samples had safe or undetectable levels of DDX.
Overall, the results of this study indicate that OCP residues persist at relatively low levels in some marine organisms and sediments in the immediate vicinity of the chemical plant in Mapua but are not of major concern for human consumption.
The low levels of pesticide residues are unlikely to explain localised mortality events in tuangi beds in the Waimea Estuary.

This single-volume guide describes over 400 of the more common marine fishes caught by bottom, midwater, and surface fishing methods in New Zealand seas. The guide is intended for field use particularly by fisheries observers and researchers who may or may not have specialist knowledge about the taxonomy of fishes. Accurate and rapid identification of catches at sea is important for obtaining good quality data about fish catches, for monitoring changes in fish abundance and enabling fisheries managers to make informed decisions about fishstock sustainability.

This guide was produced in 2024 and is a modified republication of the single-volume guide published in 2019 which replaced the three-volume set of guides published in 2011. A second version for fishers is identical except it does not include the research codes.

This single-volume guide describes over 400 of the more common marine fishes caught by bottom, midwater, and surface fishing methods in New Zealand seas. This “Fisher version” is intended for field use by fishers who may or may not have specialist knowledge about the taxonomy of fishes. The guide has been produced to support inshore fishers with their electronic reporting requirements.

This guide was produced in 2024 and is a modified republication of the single-volume guide published in 2019. A second version was produced in 2024 for scientific users and is identical except it includes codes specifically for research use.

Antipodean albatross breed at Antipodes Islands, to the south of New Zealand. Its population has been declining since 2005. Data collected since 1994 were used to make a model of the albatross population. The model showed that the number of albatrosses, their survival rates (especially for females), and their breeding rates have all decreased. This study looked at whether fishing, climate change, plastic pollution, and diseases could be causing the population decline. To find out, the study looked at where the albatrosses go when they are away from Antipodes Island. Female albatrosses spend more time in the Tasman Sea and north-east of New Zealand than males do. The study didn’t find one clear reason for the albatross decline. But, it suggested that an increase in tuna fishing in the Tasman Sea, after 2006, might be a factor. The study suggested that we need more information on albatross captures by tuna fishing vessels in the Tasman Sea.