Snapper are the most important recreational fish species in New Zealand and are often released back to the sea after capture.
Little is known about the survival of fish after they are released.
NIWA conducted a study using volunteer fishers to catch 960 snapper at different depths and with different hook placements.
The captured snapper were kept in holding nets and monitored by NIWA divers over several days.
Fish hooked in the lip had a low chance of dying if caught at shallow depths, but the chance of dying increased as depth increased.
Fish hooked elsewhere on the body had a higher chance of dying, with those hooked deep in the gut having the highest chance of dying.
This study suggests that fishing practices can impact fish survival, but there are ways to potentially reduce post-release mortality.
Understanding how fishing affects fish survival is therefore an important consideration for catch and release fisheries and when setting catch limit regulations.

This report summarises commercial catch and effort statistics for rock lobsters, which are also known in New Zealand as “crayfish” or “kōura”.

The summaries presented in this document cover the rock lobster legal fishing years (1 April–31 March) for April 1979 to March 2023.

There are nine Quota Management Areas (QMAs) that cover all inshore waters of the North Island, the South Island, and the Chatham Islands. There are 43 smaller statistical areas that lie within these nine QMAs. The summaries are ordered by QMA, with each QMA identified by a three-letter code and a number. The rock lobster code is CRA, so the nine QMAs are labelled CRA 1 to CRA 9.

The first three tables for each CRA QMA summarise, by statistical area and fishing year, (1) number of vessels, (2) catch, and (3) effort. The last category is defined as the total number of rock lobster pots lifted within each fishing year and statistical area. The fourth table summarises catch by month and fishing year for the entire QMA, and a fifth table gives the monthly catch by statistical area for just the final fishing year, which is 2022–23 in this document.

The sixth table for each QMA summarises catch-per-unit-effort (CPUE) by statistical area and fishing year. CPUE in this table is defined as the catch (in kilograms) from the second table divided by the number of potlifts in the third table. There is a seventh table providing CPUE that has gone through a mathematical procedure called “standardisation” which attempts to factor out aspects of the CPUE which might change over time. The standardisation procedure has been suspended beginning with 2019–20 because there are comparability issues associated with the changeover from paper forms to electronic reporting.

This study estimated the post-release survival of inshore finfish with current commercial minimum legal sizes—blue cod, blue moki, butterfish, kingfish, red moki, red cod, sand flounder, snapper, tarakihi, trevally, and yellowbelly flounder—and those currently allowed to be returned under disposal code X— kingfish, rig, sand flounder, school shark, rough skate, smooth skate, and spiny dogfish.

A questionnaire was developed and circulated to fishers, fishery observers, and scientists with knowledge of each species to obtain their estimates of at-release survival (i.e., the probability the fish/shark was alive when put back into water) and post-release survival (the probability an individual was both alive at release and survived following release). Estimates were obtained for each gear type as well as fishing categories within each gear type, e.g., duration, depth, and bag size. For some species, estimates of post- release survival were informed by literature on the survival of same or similar species.

These data were used with fishery characterisations to model the survival for each species. For species with a minimum legal size, both at-release and post-release survival estimates were used, whereas for those species released under disposal code X, which may only be released if alive and likely to survive, only the post-release survival estimates were used.

The post-release survival from longlines for snapper, kingfish, and rough skate (assuming they are released alive) was “medium-high”, i.e., the lower bootstrapped 90% confidence range was lower than 0.50, but greater than 0.25, and upper 90% confidence range exceeded 0.75. The same survival range was estimated for snapper caught in pots. For snapper, this result was based on expert knowledge and incorporated literature-based mean values based on empirical studies for this species in New Zealand.

However, for rough skate, the result was based on the informed opinion of 2 science experts only (at-vessel survival was assumed to be 100%) and without the benefit of literature-based empirical estimates as none exist for this species. If at-release survival estimates are included for kingfish, the range decreases to “medium”. For blue cod, and other sharks, skates, and rays, survival from capture on bottom longline was “medium-low”. Red cod survival was “low”, and an “uncertain” outcome was applied to smooth skate and blue moki due to the lack of available knowledge. For species such as spiny dogfish and school shark, the lower range of perceived survival was at least partially a result of the wide range of depths where these species are discarded, which includes deepwater fisheries with larger vessels and potentially different handling practices.

Post-release survival of most species from trawl gear was perceived to be “medium-low” at best, with 90% confidence range either spanning 0.25 up to but less than 0.75, or else between 0.25 and 0.5. Blue cod, red cod, flatfish, and tarakihi were considered in the “low” range, where the 90% confidence range did not exceed 0.25. Survival of both rough and smooth skates in trawl gear was “uncertain”, based on the lack of empirical data for these species and the wide range of estimates for related species in overseas fisheries. Where bottom trawl with a Modular Harvest System cod-end was considered as a separate gear, the lack of available data on this gear type meant survival was considered “uncertain”. For set net, the perceived survival of all species where this gear was considered an important method, was “medium-low”.

The species-method survival confidence ranges presented in this report are based on the best currently available expert knowledge and thorough reviews of the current survival literature; as such, these ranges are unlikely to be improved upon without further investment in release survival research.

This project estimated survival of six pelagic species (southern bluefin tuna, Pacific bluefin tuna, swordfish, blue shark, mako shark, and porbeagle shark) following release from commercial fishing gear to inform a government review of their landing exceptions.

Fishery characterisations revealed that the main fishing gears responsible for discarded fish were surface longline (all species) and trawl (swordfish, mako, and porbeagle).

Literature reviews were conducted to document current knowledge on the status of an individual when brought to the vessel and ‘post-release’ survival (i.e., survival in the weeks to months following release) from these methods, as well as the factors that affect survival of each species. The key results were:

Bluefin tunas (including southern bluefin tuna and Pacific bluefin tuna) and swordfish typically have high post-release survival following capture by surface longline, with most studies reporting survival rates of 88% or greater for bluefin tunas and 50–88% for swordfish.
Blue shark have high at-vessel and post-release survival following capture by surface longline, with most studies reporting at-vessel and post-release survival rates of > 80%.

Mako have moderate to high at-vessel and post-release survival following capture by surface longline, with most studies reporting at-vessel and post-release survival rates ranging from about 50–87% and 56–94%, respectively.
Porbeagle have moderate to high at-vessel survival and variable post-release survival following capture by surface longline, with estimates of 56–79% and 25–90% for at-vessel and post-release survival, respectively.
There have been no comparable studies documenting at-vessel or post-release survival of swordfish, mako, or porbeagle from trawl.

A questionnaire was developed and circulated to fishers, fishery observers, and scientists with knowledge of each species to obtain their estimates of at-release survival (i.e., the probability the fish/shark was alive when put back into water), post-release survival, and combined survival (the probability an individual was both alive at release and survived following release) of the three shark species, and post-release survival of the thee fish species (in accordance with their current landing exceptions).

Questionnaire responses were used to derive survival probability range estimates for each species, with separate analyses conducted that included and excluded information from the literature.

For individuals released after capture by surface longline, the results of this analysis indicated post-release survival for southern bluefin tuna, Pacific bluefin tuna, and swordfish is likely to be high; blue shark are likely to have high at-release and post-release survival, and a medium-high combined survival; mako are likely to have medium at-release and medium-high post-release survival (reduced to medium if excluding information from the literature in the analysis), and low-medium combined survival; and porbeagle are likely to have low at-release survival, low-medium post-release survival, and low combined survival.

Post-release survival of swordfish released from trawl gear was likely to be low, and mako and porbeagle caught by trawl were likely to have low at-release, post-release, and combined survival.

These results, however, resulted from a small number of survey responses (only one respondent for trawl gear) and often without any comparable supporting published studies.

Survival estimates presented here should thus be interpreted with caution.

Photo surveys are used to estimate abundance of scampi in New Zealand and provide important information for stock assessments.

Readers identify features in the survey photos as burrows or scampi. A statistical model is applied to produce an estimate of abundance for each survey. The statistical model takes into account differences between readers’ interpretation of features (what looks like a burrow to one reader may not to another) and differences in interpreting features over time (e.g., a reader may become more skilled at interpreting features over time, or technology could improve).

This report provides a review of the statistical model applied to produce an estimate of abundance from scampi photo surveys. The review found no concerns with the model or how it is being applied. Two readers re-read images from recent survey years to test if the adjustment over time has been appropriate. The results of the re-reads supported the model results.

Further work is suggested, including contracting a specialist statistician to provide greater theoretical understanding of the model and assumptions.

South Island recreational blue cod fisheries are monitored by Fisheries New Zealand using potting surveys to assess the status of the stocks. The results of the Foveaux Strait surveys are important inputs for full quantitative stock assessments conducted for BCO 5 every five years.

This report describes the results of the random-site blue cod (Parapercis colias) potting survey carried out in Foveaux Strait in February 2023—as well as for three previous surveys (2010, 2014, and 2018). Estimates are provided for population abundance, size structure from fish length, and age structure from otoliths (ear bones collected for ageing), as well as population sex ratio, total mortality, and fishing mortality.

The overall weighted mean length of blue cod in 2023 was 32.0 cm for males and 28.5 cm for females, and mean age was 5.9 years (1–11 years) for males and 6.2 years for females (1–16 years). There were no clear age class modes in 2023 and little evidence of spawning activity during the survey.

The scaled length frequency distributions and mean length of all blue cod were similar for all four surveys, although, in 2023, the proportion of small males was less than in previous years.

Survey abundance (total blue cod mean catch rate) from the four surveys significantly increased between 2010 and 2014, with no change in 2018, followed by a significant decline of 57% in 2023.

The proportion of pots with no catch was similar for the first three surveys (25 to 32%), but in 2023 this increased to 49%. There were no trends in sex ratio over the time series which was around 50% male.

The age structure was similar among the four surveys with most fish between 4 and 8 years of age and relatively few fish over 10 years, particularly males. The fishing pressure is concentrated on just a few older cohorts, some of which are poorly represented.

Relative to the target reference fishing mortality of F=0.15 for blue cod, the estimated mortality in 2023 was nearly seven times higher, indicating that overfishing is occurring. Fishing mortality was also considerably higher than the target for all three previous surveys.

New Zealand’s Hector’s dolphins are an endangered species. A key threat to their survival is entanglement in fishing gear, including trawl nets. In this study, we report on a field trial where underwater microphones (hydrophones) were fitted to trawling equipment and the echolocation clicks naturally produced by Hector’s dolphins were localised to determine how the dolphins interacted with the trawling equipment as it moved through the water. The hydrophones were protected within custom-built cages to withstand the physical stress associated with being attached to fishing equipment that is dragged along the seabed. The field trial was conducted off the coast of Timaru, New Zealand, in September and October 2022. While the hydrophones recorded dolphin sound underwater, a Fisheries New Zealand observer on the boat also looked out for dolphins.

The protective cages around the hydrophones proved effective and we were able to successfully localise dolphins. Dolphins were localised moving towards the mouth of the fishing net from various approach angles, and, on several occasions, we were able to successfully distinguish multiple dolphins each moving along different paths. Even though we only analysed a subset of the acoustic data from each trawl, dolphin clicks were detected acoustically during trawls on more occasions than the observer on the fishing boat was able to see dolphins. Unfortunately silt from the seabed entered some of the connections between the hydrophones and the acoustic recorder, which resulted in corrupted data on some days, but overall the field trial was successful.

This study showed that listening for the presence of dolphins can be more effective than looking for dolphins from a boat. We suggest that a combination of listening and looking for dolphins would be the most effective way to detect dolphins that might be near the fishing net. In the long term, the listening system described here could be developed into a real-time warning system that alerts the fishing vessel master when dolphins are close to the fishing net. If the vessel master is aware of the dolphins, they could avoid activities that result in high-risk of entanglement, such as sharp turns or drawing in the net at the end of the trawl. Dolphin detection could also help with targeted use of devices that encourage the dolphins to move away from the high-risk areas—such devices emit noise and should be used as little as possible to minimise noise pollution and disturbance to the dolphins.

Sea urchin barrens are sea urchin dominated areas of rocky reef that would normally support healthy kelp forest, but have little or no kelp due to overgrazing by sea urchins.

This review updates our understanding of sea urchin barrens in New Zealand and the role fishing plays in their establishment to date. It also identifies key work required to support management decisions, including collating data on the distribution of urchin barrens, reviewing information required to set catch limits for sea urchin predators, and developing regional management approaches.

We review published scientific literature on sea urchin barrens in New Zealand and the role of fishing in their development.

We also summarise results of a national workshop to support management of sea urchin barrens.

Research based on observations from marine protected areas suggests fishing of sea urchin predators is causing and/or maintaining sea urchin barrens in north-east New Zealand.

The extent of sea urchin barrens and contributing factors in other parts of New Zealand appear to vary, but there are few published studies on this.

Workshop discussions indicated an urgent need to develop a suite of management options to address sea urchin barrens at regional scales in collaboration with tangata whenua and stakeholders.

Changes in blue cod populations off Canterbury and in the Marlborough Sounds has raised concerns about the impact of human stressors on these populations, but the relationship between most stressors and blue cod is unknown.

Information on blue cod abundance was matched with environmental data to understand the habitat characteristics important for blue cod adults and juveniles off three Canterbury sites; Banks Peninsula, Motunau, Kaikōura.

Changes in potential stressors to blue cod habitat were compared with blue cod population status over 20 years at the sites off Canterbury and in the Marlborough Sounds.

Blue cod were associated with areas where the seafloor is rough and complex (e.g., reef systems), where structural habitat was provided by plants and animals, and in areas with higher water clarity and lower temperature.

Blue cod population status was related to stressors from land use (e.g., coastal water quality), and increasing water temperatures in most locations, although the intensity of these stressors has varied substantially over time and among locations.

This information provides guidance on the scale and focus for future research and potential management opportunities to limit these stressors and ensure sustainability of the blue cod fishery.

This study used a model of individual eco-physiological response to environmental and climate factors to derive population level outcomes of fish stocks. These simulations were used to investigate how fisheries stock assessments are influenced by climate and bottom-up variability in production parameters. The assessments generally provided unbiased estimates of stock status even though there were annual and decadal fluctuations in all production-related parameters.

Drivers of long-term change in the Foveaux Strait oyster fishery (OYU 5) including the effects of disease and dredging essential oyster habitat are investigated. High densities of oysters are determined by recruitment and mortality from Bonamia exitiosa. Regular recruitment to the population shows productivity of the oyster fishery is high and is not likely to have changed. Oyster factors, co-infections with other pathogens, and climatic variables may affect oyster mortality and recruitment.

A novel spatial risk assessment framework is proposed, based on the Spatially Explicit Fisheries Risk Assessment (SEFRA) and the Sustainability Assessment for Fishing Effects (SAFE). Risk is the probability that exploitation exceeds the Impact Sustainability Threshold (IST). Exploitation is estimated from the catchability and effort, using prior information on either the catchability or the population size. It is applied to shark and turtle species with different data characteristics.

Characterisation and CPUE (catch-per-unit-effort) analysis for SCI 1 (Bay of Plenty) and SCI 2 (Hawke Bay-Wairarapa) scampi (Metanephrops challengeri). Scampi live in burrows and variability in emergence rates impact the relationship between CPUE and abundance. SCI 1 index increased from 2016 to 2021. SCI 2 CPUE generally declined from 2015 to 2021. The CPUE indices were accepted by the New Zealand Fisheries Deepwater Working Group as valid for tracking scampi biomass for use in the stock assessment.

While effects of organic enrichment on inshore, soft-sediment communities are well studied, little is known about how finfish farm-derived impacts will manifest in open ocean environments. This report identifies key species that may be affected by open ocean aquaculture and describes physiological indicators that may provide insight into organism health. This is the first of several project objectives that work toward developing environmental health measures for use in offshore environments.

The impact of video monitoring on estimating black petrel bycatch in bottom longline fisheries was assessed. Combining observer and video monitoring data resulted in lower estimated captures compared with using observer data alone. Simulations of different proportions of assessed video footage suggest currently overpredicted estimates of black petrel captures. Also, the analysis suggests that the presence of observers and/or cameras increased fishers’ compliance to report black petrel captures.