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Ling and hake are tertiary consumers, and as a result both may have an important structuring role in marine communities. The diets of 2064 ling and 913 hake from Chatham Rise, New Zealand, were determined from examination of stomach contents. Ling was a benthic generalist, and hake a demersal piscivore. The diet of ling was characterised by benthic crustaceans, mainly Munida gracilis and Metanephrops challengeri, and demersal fishes, mainly Macrourids and scavenged offal from fishing vessels. The diet of hake was characterised by teleost fishes, mainly macrourids and merlucciids. Multivariate analyses using distance-based linear models found the most important predictors of diet variability were depth, fish length, and vessel type (whether the sample was collected from a commercial or research vessel) for ling, and fish length and vessel type for hake. There was no interspecific predation between ling and hake, and resource competition was largely restricted to macrourid prey, although the dominant macrourid species predated by ling and hake were different. Cluster analysis of average diet of intraspecific groups of ling and hake confirmed the persistent diet separation. Although size is a central factor in determining ecological processes, similar sized ling and hake had distinctly different foraging ecology, and therefore could influence the ecosystem in different ways, and be unequally affected by ecosystem fluctuations. [ABSTRACT FROM AUTHOR]

Southern blue whiting target strength (TS) results from Kirchhoff modelling of swimbladder casts scanned using a hand-held 3D laser scanner are presented. The data are compared with the relationship between TS and fish length used for New Zealand stock-assessment surveys; TS=21.8log10(fork length)−72.8, at 38kHz. This relationship has its origins in the relationship used for blue whiting (Micromesistius poutassou) in the northern hemisphere, and is based on measurements on juvenile cod (Gadus morhua). The results indicate that the blue whiting relationship is not appropriate for southern blue whiting, and suggest a much steeper slope, with TS=38log10(fork length)−97, at 38kHz. Sensitivity analyses indicate that further investigations of swimbladder tilt-angle distribution and swimbladder volume are unlikely to provide evidence to support the use of the blue whiting relationship for southern blue whiting. [Copyright &y& Elsevier]

The prevalence of acute and healed fin erosion in goldfish, Carassius auratus (L.). from the Waikato River, New Zealand, peaked in the vicinity of a pulp and paper mill which utilized a kraft pulping process in association with chlorine bleaching, and decreased down the effluent gradient. About 49% of goldfish sampled from the Kopakorahi Stream, which is part of the effluent treatment system (site 1), displayed pathological signs of fin erosion, whereas about 9% of control fish from a reference site located upstream of the official effluent discharge point were similarly affected. Fin erosion was less prevalent in male than in female goldfish, and occurred with different frequencies on different fins, the pectoral (56%) and caudal fins (33%) being most affected. Both the pectoral and caudal fins also had significantly higher proportions of healed erosion rather than acute erosion. The prevalence of acute and healed fin erosion increased significantly with increasing fish length (age). Physical deformities, predominantly in the form of eroded or otherwise malformed opercula, were found in nearly 5% of fish caught at site 1, but were not observed at the reference site. Changes in processing and bleaching technology at the pulp and paper mill in question have since been carried out, and long-term studies are planned to monitor any subsequent improvements in fish health. [ABSTRACT FROM AUTHOR]

Īnanga (Galaxias maculatus) is a widespread freshwater fish, found around coastal New Zealand, Chatham Islands, southern Australia and southern South America, exhibiting both diadromous and land-locked life history patterns. We assessed population size structure, size at maturity, timing of reproduction, and post-reproductive survival in the Waikouaiti and Kakanui rivers, two regionally important G. maculatus populations in southern New Zealand. Size at maturity varied between rivers and sexes, with males generally maturing at smaller sizes than females. The timing of reproduction and recruitment was observed to vary across a relatively small spatial scale. Population length-frequencies indicated that both populations exhibited annual population dynamics, with most individuals spawning in their first year, then apparently dying soon afterwards (as indicated by a marked drop in post-spawning abundance). However, a few individuals with recently spent or resting gonads were present over the winter months, indicating some post-spawning survival. There was a lower frequency of exceptionally large (putatively 1+) individuals than reported for other populations around New Zealand and elsewhere, suggesting over-winter survival following spawning varies. Based on the variation in life history characters over small spatial scales, we suggest that management of regionally important G. maculatus populations should be based on catchment level information. [ABSTRACT FROM AUTHOR]

Growing demand for water requires resource managers to be innovative to minimise impacts on aquatic ecosystems. There are increasing concerns about fish damage and losses at water intakes, but few studies have examined the effectiveness of different screening material for excluding New Zealand fishes. We experimentally tested six screens (50–100 and 100–200 mm rock bunds, 3 mm woven mesh, 1.5, 2 and 3 mm wedge-wire), on two introduced and five native fish species. Bluegill bully (> 32 mm), common bully (> 30 mm), Canterbury galaxias (> 47 mm) and rainbow trout (> 40 mm) were screened effectively by 3 mm woven mesh and wedge-wire. Chinook salmon (> 43 mm) and īnanga whitebait (> 46 mm) were excluded by 2 mm wedge-wire, but shortfin elvers (< 80 mm) penetrated 3 and 2 mm wedge-wire, and glass eels (< 63 mm) penetrated 1.5 mm wedge-wire. Rock bunds were effective barriers for rainbow trout but were ineffective, and acted as habitat, for bluegill bully, Canterbury galaxias and shortfin eels. We recommend that 1.5 mm wedge-wire screens are used in the tidal zone of New Zealand rivers, 2 mm screens are used beyond this zone with an upstream transition to 3 mm screens dependent on catchment-specific fisheries values. [ABSTRACT FROM AUTHOR]

The presence of wild fish in and around aquaculture habitats is often assumed a response to food resources within these habitats, either from input feed, the presence of cultured species, and/or the assemblage of biofouling that naturally colonises aquaculture structures. The nutritional quality of the food resources consumed by wild fish in aquaculture habitats is also important in determining their nutritional condition and subsequent productivity. Few studies have investigated the nutritional quality of prey in aquaculture habitats, and these have mostly focused on fed aquaculture by tracking manufactured fish pellets into the diets of wild fish. However, in non‐fed aquaculture, the assemblage of cultured and biofouling species may also provide a nutritional benefit to fish feeding in these habitats. The Australasian snapper, Chrysophrys auratus, are commonly present as adults within coastal mussel farms in New Zealand and tend to become a resident species. This study investigated the nutritional quality of the gut contents of snapper in soft‐sediment habitats within and outside of New Zealand green‐lipped mussel farms. Total lipid, protein, carbohydrate and total calorific content were measured from the gut contents of snapper sampled from mussel farm and natural (i.e. control) habitats. Snapper in mussel farms had double the dietary intake of lipid (16% vs. 8%) from consuming lipid‐rich bivalves and barnacles which are in abundance in mussel farms. Higher lipid intake can contribute to improved nutritional condition, reproduction and growth in snapper. However, the higher dietary lipid intake of snapper in mussel farms did not increase their overall body condition (i.e. Fulton condition index). This may be due to the coarse nature of this measure, or the use of the additional lipid in more rapid somatic growth or reproductive outputs, possibilities that warrant examination through further research. Overall, this study shows for the first time the potential ecosystem benefits of shellfish aquaculture in provisioning nutritionally valuable prey for coastal fish populations. [ABSTRACT FROM AUTHOR]

Kloser, R. J., Ryan, T. E., Macaulay, G. J., and Lewis, M. E. 2011. In situ measurements of target strength with optical and model verification: a case study for blue grenadier, Macruronus novaezelandiae. – ICES Journal of Marine Science, 68: 1986–1995.In situ measurements of target strength (TS) of isolated fish surrounding dense schools need to be representative of the schooling fish to calculate their echo-integrated biomass. Using synchronous optical and acoustic measurements from a pelagic fishing net, the standard length (81 cm, n = 128), tilt-angle (−9°), and net-disturbed in situ TS (−34.4 dB) of Australian Macruronus novaezelandiae (blue grenadier) were confirmed at depth. In situ drift experiments of assumed undisturbed but dispersed blue grenadier recorded a mean TS of −31.8 dB (CI −33.1 to −30.9 dB) with attributed fish standard lengths of 83 cm (s.d. 7.5 cm) and weight 2.5 kg. Modelling the gasbladder showed that uncertainties in fish length, orientation, and gasbladder size could explain the differences observed. Blue grenadiers have negative buoyancy because the cavity size of their gasbladder is smaller than the volume of gas required for neutral buoyancy at depth. For the same species and length, New Zealand hoki weigh less and have smaller gasbladders than Australian blue grenadier, suggesting a conversion factor of 1.10 in length for comparative measurements. Net-attached acoustic and optical measurements indicate that model and drift in situ measurements are biased high by 2.9 and 1.0 dB, respectively. Net-attached acoustic and optical measurements are a cost-effective method of monitoring TS routinely at depth for changes in species length and weight. [ABSTRACT FROM PUBLISHER]

Larval behaviour for many of New Zealand's diadromous freshwater fish is inadequately described. Diadromy for many amphidromous species is not obligatory however, and where conditions are suitable, freshwater larval rearing may be facilitated. Where this occurs in lakes, opportunities to document the composition and conditions supporting larval rearing exist. Boat trawling was undertaken across nine lowland lakes in the Lower Waikato over four consecutive winters with a focus on larval galaxiids. Galaxiid larvae were captured in surface water habitats in all but one lake, with banded kōkopu (Galaxias fasciatus) and giant kōkopu (Galaxias argenteus) the most common species detected. One lake, Lake Waahi, consistently resulted in the most galaxiid captures for effort expended. Analyses of larvae from this and other lakes indicated that two sizes predominated in catches and that larger, older larvae were predominantly G. fasciatus while smaller, younger larvae were predominantly G. argenteus. Stomach contents indicated that two non-native zooplankton species predominated in the diet of larvae, the Holarctic daphnia, Daphnia galeata, and the Australian calanoid copepod Boeckella symmetrica. This study provides new information regarding the timing, movement and predicted recruitment of native fish species in this river basin that has important implications for lake and river management. [ABSTRACT FROM AUTHOR]

The fluctuating asymmetry values of the two otolith parameters: length and width of Engraulis australis, recovered from the food of gannet, which inhabit colonies in islands at Hauraki Gulf, New Zealand was calculated in this study. The dissimilarity value of the otolith width was higher than that of the otolith length. An inclination of upsurge in the dissimilarity values with the fish length was noted for the otolith sizes studied. The dissimilarity value in the two otolith sizes was the lowest for fish having total length of 115–154 mm, and the highest for fish with length of 151–160 mm. The conceivable reason of the dissimilarity obtained could be related to diverse contaminants and their presence in the study location. • The fluctuating asymmetry value of the two otolith parameters length and width of Engraulis australis was calculated. • The level of asymmetry of the otolith width was higher than for otolith length. • A tendency of increase in the asymmetry values with the fish length was observed for the otolith length and width. • The lowest level of asymmetry examined is for fish between 115-154 mm in length and the highest between 151-160 mm. • The possible reason of the asymmetry has been discussed in the area in relation to pollution. [ABSTRACT FROM AUTHOR]

The accumulation of parasites in a fish host is modelled as a function of the total amount of prey consumed. The accumulated parasite load is then expressed as a function of fish length so that the asymptotic growth, L, of any population of commonly infected fish can be estimated. Estimates of L are obtained for orange roughy ( Hoplostethus atlanticus), albacore tuna ( Thunnus alalunga) and the New Zealand southern arrow squid ( Nototodarus sloanii). [ABSTRACT FROM AUTHOR]

Composition and length-frequency are important attributes considered in the management of fish communities and can be affected by both exploitation and environmental forces. Vulnerability to these effects varies among species depending on environmental tolerance, ecological traits, and life-history strategies. In the present study, data from scientific bottom trawl surveys conducted between 1991 and 2018 were analysed to identify long-term changes in community structure and length-frequency of demersal fish species of the east coast of the South Island, New Zealand. Analysis of variance, hierarchical clustering analysis and multidimensional scaling relationships demonstrated that community composition has changed significantly over the last three decades, with a tendency towards greater spatial overlap among species in the most recent periods. Changes in depth distribution were identified but were mainly correlated with shifts in relative biomass. Total catch rate (kg km−2) of the whole community has increased significantly over time, while the average trophic level decreased, primarily explained by an increase in relative biomass of intermediate trophic level species. Fishing activity was significantly related to the variation in length-frequency of species at intermediate trophic levels, confirming that the impacts of fisheries are heterogeneous throughout the community, providing vital information to support multi-species management of fishery resources. [ABSTRACT FROM AUTHOR]

Amphidromous fishes engage in migration to overcome the spatial mismatch between adult and larval habitat. The torrentfish (Cheimarrichthys fosteri), an endemic New Zealand amphidromous fish and only member of the Family Cheimarrichthyidae, display distinct spatial sexual segregation, but the migration assumed to overcome this segregation for reproduction is undocumented. We investigated the instream distribution of torrentfish, gaining insight into how barriers to reproduction are overcome, and how sex shapes migratory choices for the individual. We surveyed torrentfish at two spatial scales, examining the effects of sex and sexual maturity on distribution. We found that female torrentfish engage in prolonged upstream migrations, up to 100 km inland, with male torrentfish migrating upstream to a lesser extent. Both sexes return downstream to spawn, with males returning at the onset of maturity, while females may return and migrate back upstream, potentially making multiple downstream spawning migrations. Juvenile upstream migration likely results in competitive release and access to resources, but sets up a conflict between reproduction and transport of larvae into the nursery habitat in a timely manner. Adult downstream migration in torrentfish resolves this conflict and is similar to documented downstream spawning migrations in catadromous species. [ABSTRACT FROM AUTHOR]

Spatio-temporal modelling frameworks are important tools for evaluating changes in the population structure of freshwater species, to inform population assessments. However, in the stream networks occupied by freshwater species, two data points in space are more related by physical connectivity than by straight-line, Euclidian distance. Therefore, there is a need for spatio-temporal modelling frameworks that represent the relatedness of points based on physical connectivity. We developed such a modelling framework, known as the "VAST stream network modelling framework", using the widely-employed vector autoregressive spatio-temporal modelling platform VAST and the Ornstein-Uhlenbeck process for spatial variance. Here, we demonstrate the VAST stream network spatio-temporal modelling platform with two applications to the freshwater stages of a diadromous fish species, the endemic New Zealand longfin eel (Anguilla dieffenbachii), and a simulation experiment. The first real-world application considers a single category (longfin eel) and models its probability of encounter in the Waitaki catchment, while the second distinguishes between two categories (smaller and larger longfin eels) and models their numerical densities in the greater Waikato region. These two applications demonstrate how stream network spatio-temporal models can usefully inform freshwater resource managers, providing insights into changes in fish encounter probability and density for different fish length classes and estimates of effective river length occupied. The simulation experiment uses the Waikato model as an operating model to evaluate alternative sampling scenarios for accuracy, precision and coverage, to advise on data requirements. A yearly sample size of 30 sites over a 20-year time series had the greatest precision and accuracy in trend estimates among all scenarios investigated. We also found that, for the scenario with declining female spawning biomass, increasing the yearly sample size from 15 sites to 30 sites in a 9-year time series increased the precision and resulted in unbiased estimates. There is a need to optimise sampling schemes for the freshwater stages of diadromous species, including longfin eel, and we, therefore, recommend further simulation experiments to explore scenarios of population trends, habitat features and sampling approaches. • We developed a VAST stream network modelling framework. • Two New Zealand longfin eel (Anguilla dieffenbachii) case studies and a simulation experiment are presented. • The case studies highlighted changes in density and effective river length occupied. • The simulation experiment demonstrated a need for optimization of sampling schemes. [ABSTRACT FROM AUTHOR]

The early Miocene palaeolake Manuherikia in Central Otago, South Island, New Zealand is a prime source for reconstructing the terrestrial and freshwater biota of past Zealandia. Otoliths of fishes that once lived in this lake system were first described in 2012. Here we report the results of extensive additional sampling resulting in a total of 16,500 fish otoliths from a wide set of stratigraphic levels and environmental settings within the Bannockburn Formation near St Bathans. Six new species are described: Galaxias crassus, Galaxias naviculus, Galaxias nitidus, Galaxias polei, Galaxias tholus, Mataichthys asymmetricus. The entire freshwater otolith-based fish fauna of the Bannockburn Formation now encompasses 17 species, 10 in Galaxiidae, 2 in Prototroctidae and 5 in Eleotridae; all families present in the freshwater systems of New Zealand today. Correlation with putative related extant taxa reveal that the fishes from the Bannockburn Formation were relatively large, often at the upper margin of the extant sizes of fishes in the respective groups or even larger. This 'Gulliver' fish fauna is consistent with other fossil and extant 'gulliverisms' observed in various Zealandian biota. Environmental and putative evolutionary explanations, aspects of the taphocoenosis and possible stratigraphic implications of the otolith assemblages are discussed. [ABSTRACT FROM AUTHOR]

Hoki ( Macruronus novaezelandiae ) is New Zealand's largest fishery. Acoustic surveys of spawning hoki provide abundance indices for informing management of the stocks. For estimating fish abundance using acoustic methods, relationships between the acoustic backscatter from a single fish, commonly known as the acoustic target strength (TS), and fish length are required. Here we present in situ data on TS from individual live hoki, collected using a trawl-mounted acoustic-optical system (AOS). Deriving TS–length relationships from measurements of individual fish is complicated because of the very large stochastic variability in TS from the same fish, and from individual fish of similar length. A new TS–total length relationship of TS = 24.5log 10 (TL) − 83.9 was derived based on a weighted non-linear least-squares fit to acoustic backscattering cross-section measurements from 62 New Zealand hoki between 35 and 93 cm TL. It was necessary to use a weighted fitting method to appropriately account for variance, as not doing so can introduce a bias to the estimated mean TS. Using the new TS–TL relationship decreases absolute estimates of hoki abundance by 50–60% from those currently used in stock assessment, but has little impact on relative indices. Estimated 90% confidence intervals around the new TS–TL relationship based on bootstrapping suggested uncertainty in mean TS of ±1.5 dB at typical New Zealand hoki lengths, with resulting uncertainty in abundance estimates of up to 50%. Further in situ measurements and modelling are required to reduce this uncertainty and to investigate potential differences in TS between AOS-measured and ‘undisturbed’ fish. [ABSTRACT FROM AUTHOR]

Aquatic food‐web studies involving fish and using stable isotope analysis typically sample fish white muscle, which generally requires the fish to be euthanised. Alternatively, fin tissue can be sampled non‐lethally, avoiding the need to euthanise an animal to obtain what is usually a relatively small tissue sample. We set out to develop equations for converting δ13C and δ15N values from derived non‐lethally sampled fin tissue to equivalent white muscle tissue, for use in food‐web studies. We explored δ13C and δ15N values of paired fin‐clips and white muscle from two species of anguillid fishes, the endemic longfin eel (Anguilla dieffenbachii), and the Australasian shortfin eel (A. australis), sourced from multiple studies spread throughout New Zealand. We also examined the effect of lipid extraction on δ13C and δ15N, which reduced variability of δ13C when compared to untreated samples. We were also able to estimate δ13C values of equivalent lipid‐extracted muscle samples directly from untreated fin. For δ15N, paired untreated fin and muscle values were not statistically different so fin δ15N can be used as a direct estimate of muscle δ15N. Solvent lipid extraction with a methanol–chloroform mixture, however, altered δ15N values and increased variability, so should be avoided. We present equations to estimate lipid‐corrected δ13C values of muscle tissue for use in stable isotope studies of freshwater anguillids, avoiding euthanasia. Our results demonstrate that δ13C and δ15N values can be accurately derived from non‐lethally obtained fin clips, reducing unnecessary mortality in fish species of conservation concern. [ABSTRACT FROM AUTHOR]

Anomalies can arise when species-specific otolith equations are applied to congeneric species in analyses of seal prey remains. Opalfishes,Hemerocoetes, two spp., are the most numerous fish in the diet of New Zealand sea lions,Phocarctos hookeri, at their population base at the Auckland Islands. Opalfish identified from otoliths in sea lion prey remains accounted for one-third of prey items in this and two previous diet studies. This highlighted the need to estimate size of opalfish accurately. Equations to estimate fish size from otolith length differed between the two species because otoliths ofH.morelandiwere relatively smaller than otoliths ofH.artus. However, otoliths of these species were indistinguishable and this precluded definitive estimates of opalfish length and mass from otoliths. In particular, misidentification of otoliths could create untenably large estimates for fish size. A combination of the equations for otolith size to fish size from the two species avoided this anomaly and superseded previously published equations. [ABSTRACT FROM AUTHOR]

Aim: Fisheries ecosystems are subject to long‐term shifts in food web structure as a result of exploitation and environmental change. These shifts can be gradual and unresolved by decadal‐scale time series. The aim of our study was to determine long‐term legacy effects of overexploitation and changes to the composition of basal organic matter sources on the trophic structure of marine food webs. Location: New Zealand. Time period: Approximately 1250 AD to the present; the complete history of human occupation in New Zealand. Major taxa studied: Mesopredatory fishes. Methods: We used whole tissue (δ13C and δ15N) and amino acid‐specific (δ15NAA) stable isotope analyses of bone collagen and muscle tissue from five fishes spanning the period of human occupation of New Zealand to resolve the bioenergetic consequences of long‐term shifts in food web structure. Stable isotope analysis of amino acids provided the basis for resolution of changes in trophic level in the absence of information on δ15N at the base of the food web during pre‐industrial times. Results: Our analyses indicate likely declines in the contribution of organic matter derived from kelps in four species, and intraspecific increases in trophic levels in three species of the five fishes studied between European colonization (AD 1650–1800) and the present‐day regime of industrialized fishing and environmental change (AD 1953–2018), but little change during the prehistoric time period spanning early Māori occupation (AD 1250–1450) to European colonization. Analysis of the bioenergetic costs of the observed shifts in food web structure indicate a 179% increase in basal organic matter requirements to support mesopredatory fish. Main conclusions: These data provide a rare case study on the consequences of legacy effects of exploitation and environmental change for bioenergetics of fish communities relevant to ongoing changes in global marine ecosystems. Overexploitation and decline in kelp forests have inflated the bioenergetic costs of these fisheries. [ABSTRACT FROM AUTHOR]

Aquaculture is the fastest‐growing food production sector worldwide, yet industry has been slow to implement genomic techniques as routine tools. Applying genomics to new breeding programmes can provide important information about pedigree structure and genetic diversity; key parameters for a successful long‐term breeding programme. It can also provide insights on potential gains for commercially important, yet complex, quantitative traits such as growth rate. Here we investigated a population of 1100 captive‐bred F1 silver trevally (Pseudocaranx georgianus), a promising new species for New Zealand aquaculture. We used whole‐genome information, coupled with image‐based phenotypic data collected over two years, to build the pedigree of the population, assess its genetic diversity, describe growth patterns of ten growth traits and estimate their genetic parameters. Successful parentage assignment of 664 F1 individuals showed that the pedigree consisted of a complex mixture of full‐ and half‐sib individuals, with skewed reproductive success among parents, especially in females. Growth patterns showed seasonal fluctuations (average increase across all traits of 27.3% in summer and only 7% in winter) and strong inter‐family differences. Heritability values for growth traits ranged from 0.27 to 0.76. Genetic and phenotypic correlations between traits were high and positive, ranging from 0.57 to 0.94 and 0.50 to 1.00 respectively. The implications of these findings are threefold: first, the best on‐growing conditions are in warmer months, where highest growth peaks can be achieved; second, size‐ and family‐based selection can be used as early selection criterion if pedigree structure and inbreeding risks are closely monitored; third, selection for body length results in concomitant increases in height and weight, traits of paramount importance for aquaculture. It is concluded that there is substantial potential for genetic improvement of economically important traits, suggesting that silver trevally is a promising species for selective breeding for enhanced growth. [ABSTRACT FROM AUTHOR]

We evaluate hypotheses for meso-scale spatial structure in an orange roughy (Hoplostethus atlanticus) stock using samples collected during research trawl surveys off the east coast of New Zealand. Distance-based linear models and generalised additive models were used to identify the most significant biological, environmental, and temporal predictors of variability in diet, proportion of stomachs containing prey, standardised weight of prey, fish somatic weight, fish total weight, and reproductive activity. The diet was similar to that observed elsewhere, and varied with ontogeny, depth, and surface water temperature. Smaller sized and female orange roughy in warmer bottom water were most likely to contain food. Fish condition and reproductive activity were highest at distances more than 20 km from the summit of the hills. Trawl survey catches indicated greater orange roughy densities in hill strata, suggesting hill habitat was favoured. However, analyses of feeding, condition, and reproductive activity indicated hill fish were not superior, despite fish densities on hills being reduced by fishing which, in principle, should have reduced intra-specific competition for food and other resources. Hypotheses for this result include: (1) fish in relatively poor condition visit hills to feed and regain condition and then leave, or (2) commercial fishing has disturbed feeding aggregations and/or caused habitat damage, making fished hills less productive. Mature orange roughy were observed on both flat and hill habitat during periods outside of spawning, and if this spatial structure was persistent then a proportion of the total spawning stock biomass would remain unavailable to fisheries targeting hills. Orange roughy stock assessments informed only by data from hills may well be misleading. [ABSTRACT FROM AUTHOR]

The article reports on a study conducted on the dietary variations of hoki fish Macruronus novaezelandiae found in New Zealand. It is mentioned that stomach content of approximately 1995 fishes of varying length collected from different depths of Chatham Rise were examined. A multivariate analysis was done which established relationship between subtropical front, fish size and longitude. The feeding activity was found to differ with time of day. A detailed discussion on the study is presented.

Age compositions from eight blue cod (Parapercis colias) subpopulations off the South Island of New Zealand were compared to investigate recruitment patterns temporally and spatially. Findings indicate (1) recruitment is highly variable between years, (2) subpopulations closer to each other have similar age compositions, and (3) strong and weak recruitment events are linked and the key processes that drive recruitment strength are acting on a large spatial scale. Recruitment variability among years and similarities between areas are likely to be density-independent, due to environmental fluctuations. Age compositions exhibited modal progression of age classes providing validation of ageing based on counts of rings on otoliths. Sex ratio by age and length were compared in relation to their reproductive strategy of changing sex from female to male (protogynous hermaphrodites). Sex ratio pattern differed for each of the eight subpopulations but was most similar in those from the same area. Males dominate at younger ages and sex ratio swings in favour of females with increasing age. Patterns in sex ratio with size are virtually the opposite to those of age because the largest fish are invariably males. These results support the theory that the form of protogyny in blue cod is diandric. [ABSTRACT FROM AUTHOR]

Diseases, and the parasitic organisms that cause them, can impact aspects of ecosystems ranging from altering food web connectivity to population dynamics. Apart from interspecific interactions, parasites can affect how their hosts behave with conspecifics, such as during competition for resources. Fish are important hosts to a variety of parasite taxa that can, through physical impairment or invasion of sense organs, affect how they interact with conspecifics for food, territory, or mates. In New Zealand, the common bully Gobiomorphus cotidianus plays host to a variety of parasites, encysting throughout the body (Apatemon sp.) or residing within the eyes (Tylodelphys darbyi). We hypothesized that fish with lower levels of infection would secure territories closer to a food patch and be more likely to tolerate sharing that territory. Our experiments show that parasites infecting different areas may have variable impacts on how far the host positions itself from a food patch and the likelihood that it shares its territory. Fish with higher intensities of T. darbyi tended to be closer to the food patch, but Apatemon sp. did not show a similar pattern. Higher infection levels of both parasites were statistically associated with bullies being less likely to share territory. Further, bigger fish were less likely to share their territory at higher intensities infection, and we observed individual variation in a fish's response between trials. Our findings support that parasites matter in ecological interactions but also emphasize the context dependence of their effects. [ABSTRACT FROM AUTHOR]

Freshwater eels are ecologically, and culturally important worldwide. The New Zealand long-finned eel (Anguilla dieffenbachii) and short-finned eel (Anguilla australis) are apex predators, playing an important role in ecosystem functioning of rivers and lakes. Recently, there has been a national decline in their populations due to habitat destruction and commercial harvest. The emergence of targeted environmental DNA detection methodologies provides an opportunity to enhance information about their past and present distributions. In this study we successfully developed species-specific droplet digital Polymerase Chain Reaction (ddPCR) assays to detect A. dieffenbachii and A. australis DNA in water and sediment samples. Assays utilized primers and probes designed for regions of the mitochondrial cytochrome b and 16S ribosomal RNA genes in A. dieffenbachii and A. australis, respectively. River water samples (n D 27) were analyzed using metabarcoding of fish taxa and were compared with the ddPCR assays. The presence of A. dieffenbachii and A. australis DNA was detected in a greater number of water samples using ddPCR in comparison to metabarcoding. There was a strong and positive correlation between gene copies (ddPCR analyses) and relative eel sequence reads (metabarcoding analyses) when compared to eel biomass. These ddPCR assays provide a new method for assessing spatial distributions of A. dieffenbachii and A. australis in a range of environments and sample types. [ABSTRACT FROM AUTHOR]

Visually verified in situ target strengths (TS) are the state of the science for determining the conversion from acoustic echo-integration surveys to biomass. Here, we show how these measurements can be made by high seas fisheries during normal operations using a net-attached acoustic optical system (AOS) without specialized personnel on board. In situ TS were collected from ∼45 cm standard length (SL) orange roughy (Hoplostethus atlanticus) in the southern Indian Ocean at 38 and 120 kHz. We use a multiple lines of evidence approach to demonstrate that the previous TS – SL equation developed for ∼10 cm smaller fish in Australia and New Zealand is not suitable for the larger orange roughy and instead propose new TS – SL equations. Our findings show that biomass estimates at 38 kHz will be reduced by ∼58% when using this new TS – SL compared to the existing TS – SL for smaller fish. This highlights the error of extrapolating TS – SL equations outside the measurement range. For this high sea region, the net-attached AOS represented a practical cost-effective method to obtain measurements and provide a result that could be used to inform the management of the stocks. We suggest that this method would be useful in all deep-water fisheries to monitor the TS of the fish for a range of environmental and ontogenetic conditions. [ABSTRACT FROM AUTHOR]

The study of phenotypic variation at the level of populations and species is central to understanding the processes that lead to evolutionary diversification. Triplefin fishes (Tripterygiidae) are a diverse and ecologically important family on New Zealand rocky reefs. This assemblage provides an opportunity to explore phenotype-environment relationships and the mechanisms responsible for the ecological speciation that is thought to have driven diversification in this clade. To test these relationships, we used two main approaches. Firstly, we used a geometric morphometric approach, and secondly, we used controlled rearing experiments in aquaria to examine the mechanism behind this phenotypic variation. The results showed that wild populations of the habitat generalist Forsterygion lapillum differed in body and fin morphology across a gradient in wave exposure in a region with extensive gene flow. Results of the tank experiments demonstrated that new recruits of F. lapillum from the same location that were raised in distinct water movement environments became morphologically distinct, whereas new recruits of F. lapillum from distinct water movement environments that were raised in identical conditions did not. The reciprocal rearing experiments, in conjunction with the morphological variation shown in wild individuals across the exposure gradient, indicate that plasticity is predominantly responsible for the phenotypic variation seen in F. lapillum populations in the Hauraki Gulf, New Zealand. [ABSTRACT FROM AUTHOR]

A potential mechanism of global decline in freshwater mussel (Unionida: Bivalvia) abundance and diversity is disruption of their obligate parasitic life-cycle by non-native fish species, which may introduce novel interaction pathways that threaten unionid recruitment. We assessed three non-native fish (brown bullhead catfish, Ameiurus nebulosus; rudd, Scardinius erythrophthalmus; and goldfish, Carassius auratus) as glochidial hosts for the New Zealand freshwater mussel Echyridella menziesii to test the hypotheses that (i) non-native fish will have lower glochidial attachment rates than a native fish (the common bully Gobiomorphus cotidianus), and (ii) encystment rate will be lower on non-native species. We found that the non-native fish had significantly lower total glochidial attachment than the native control fish after infestation and did not produce ecologically significant quantities of juvenile mussels. This research supports the general assumption that non-native species are less suitable hosts of native freshwater mussels. However, confirming our findings in the field will indicate if removing non-native fish or enhancing native fish populations is recommended for conservation of E. menziesii populations in New Zealand. [ABSTRACT FROM AUTHOR]

Fisheries harvest has pervasive impacts on wild fish populations, including the truncation of size and age structures, altered population dynamics and density, and modified habitat and assemblage composition. Understanding the degree to which harvest‐induced impacts increase the sensitivity of individuals, populations and ultimately species to environmental change is essential to ensuring sustainable fisheries management in a rapidly changing world. Here we generated multiple long‐term (44–62 years), annually resolved, somatic growth chronologies of four commercially important fishes from New Zealand's coastal and shelf waters. We used these novel data to investigate how regional‐ and basin‐scale environmental variability, in concert with fishing activity, affected individual somatic growth rates and the magnitude of spatial synchrony among stocks. Changes in somatic growth can affect individual fitness and a range of population and fishery metrics such as recruitment success, maturation schedules and stock biomass. Across all species, individual growth benefited from a fishing‐induced release of density controls. For nearshore snapper and tarakihi, regional‐scale wind and temperature also additively affected growth, indicating that future climate change‐induced warming and potentially strengthened winds will initially promote the productivity of more poleward populations. Fishing increased the sensitivity of deep‐water hoki and ling growth to the Interdecadal Pacific Oscillation (IPO). A forecast shift to a positive IPO phase, in concert with current harvest strategies, will likely promote individual hoki and ling growth. At the species level, historical fishing practices and IPO synergized to strengthen spatial synchrony in average growth between stocks separated by 400–600 nm of ocean. Increased spatial synchrony can, however, increase the vulnerability of stocks to deleterious stochastic events. Together, our individual‐ and species‐level results show how fishing and environmental factors can conflate to initially promote individual growth but then possibly heighten the sensitivity of stocks to environmental change. [ABSTRACT FROM AUTHOR]

The Chilean jack mackerel (Trachurus murphyi) is a predominantly Southeast Pacific Ocean species. It is relatively difficult to determine its age, and multiple studies of its growth off South America have produced markedly different sets of von Bertalanffy parameters. T. murphyi was first identified from New Zealand waters in the mid‐1980s and has comprised part of the commercial landings of Trachurus species (along with Trachurus declivis and Trachurus novaezelandiae) since then. Results from 13 years of age determination of New Zealand samples using sectioned otoliths indicate that a partially validated age determination method has been developed, with a precision level (average percentage error) of 4.6%. The best available von Bertalanffy growth parameters for the New Zealand population (sexes combined) are as follows: L∞, 51.9 cm fork length; K, 0.223 per year; t0, −0.5 year. Analyses by sex showed that males have a significantly larger L∞ than females. Estimated annual catch‐at‐length and catch‐at‐age distributions from the fishery are presented for 2007–2019. There have been at least two episodes of immigration of T. murphyi from international waters, but little evidence of spawning success to maintain the New Zealand population. [ABSTRACT FROM AUTHOR]

Determining the factors driving population dynamics of stream salmonids across broad landscapes is important for understanding stream ecosystem functioning and for the management and conservation of the populations of such fish. A few studies have described the determinants of the early life history of salmonids across catchments, but none of them have examined how this spatial variation develops temporally.We hypothesised that: (1) spatiotemporal dynamics of young‐of‐the‐year (YoY) trout populations vary within the catchment, with loss rates (emigration plus mortality) being higher in lower elevation, downstream reaches than in higher elevation, upstream ones; and (2) loss rate would be density dependent, leading to reduced intra‐ and inter‐cohort competition and supporting establishment of resident populations.We tested the first hypothesis by examining relationships between geomorphic characteristics of spawning streams and temporal dynamics of YoY brown trout density, loss rate and biological traits through an austral summer across the catchment of New Zealand's fourth‐longest river, the Taieri River. To test the second hypothesis, we examined whether initial YoY density in spring and other biotic determinants affected loss rate and cohort structure dynamics, resulting in density‐dependent self‐thinning of YoY fish to avoid resource limitation.Spring YoY density and subsequent loss rate was higher in low elevation sites, corresponding to stream accessibility to migratory spawners. These significant correlations of YoY density and related biotic variables with elevation disappeared later in the season, indicating that regardless of their origin, brown trout YoY tend to form stream resident populations with multicohort structure and densities low enough to limit intraspecific competition.Our findings provide evidence that geomorphological features of the landscape affect temporal dynamics of YoY trout populations driven by density‐dependent self‐regulatory mechanisms that can control the abundance of growing fish. [ABSTRACT FROM AUTHOR]

To investigate whether wild fish populations are food limited, this study explored whether the provision of supplementary food had a positive effect on the abundance, condition and growth characteristics of estuarine fish assemblages in New Zealand. Feed (7690 kg) was delivered from an anthropogenic feeding station over a 60‐week period to a naturally occurring assemblage of wild fish. Yellow‐eyed mullet (Aldrichetta forsteri) of juvenile, sub‐adult and newly matured size classes were the dominant species actively foraging at the feeding station throughout its operation, whereas larger piscivorous species visited and foraged from the feed station over the summer period only. Other species were present in the wider area of Nelson Haven, but not at the feed station. No obvious changes in the condition factor of yellow‐eyed mullet were observed across the period of monitoring, and no changes in their catchability were detected – although marked seasonal variation in catch rates was observed. Results from tag‐recapture data identify that the length‐based growth rates of yellow‐eyed mullet recaptured near the feed station were higher than those of tagged individuals recaptured at a nearby comparison site, and were higher than the growth rates observed in natural populations of yellow‐eyed mullet in the wider region. Shifts in the median size of fish, as observed by acoustic observations, agreed with the tag‐recapture data. Although some of the results identified were not amenable to statistical analyses, the attendance of yellow‐eyed mullet at the feeding station, in combination with the improved estimates of growth by most of the techniques employed, indicates that yellow‐eyed mullet are food limited in their natural environment and that the growth performance of these fish can be positively affected by the increased availability of food. [ABSTRACT FROM AUTHOR]

The demand for information on mid-trophic level (MTL) organisms in open-ocean marine ecosystems has led to initiatives to collect acoustic data opportunistically in different regions around the world. Although, bulk acoustic data can provide information on the distribution patterns and dynamics of MTL organisms, it is necessary to convert acoustic-derived indices into biologically relevant quantities for parameterising and validating ecosystem and trophic models. A 7-year time series of acoustic data collected by ships of opportunity (SOOP) in the New Zealand sector of the Southern Ocean, information on species' distribution derived from trawl samples collected in research voyages, and target strength (TS) estimates obtained using a resonance-scattering model and literature TS–length relationships, were used to obtain the first estimates of density of mesopelagic fish in this region. Estimates of mesopelagic fish density decreased from north to south reflecting changes in species composition and scattering properties across three latitudinal regions (Northern, Central and Southern). Density estimates ranged from 16.4–40.1 in the north to 4.4–13.4 g m−2 in the south. Catches revealed that the Northern region was dominated by Lampanyctodes hectoris and Protomyctophum sp. (Myctophidae) and Maurolicus australis (Sternoptychidae); the Central and Southern regions were dominated by the myctophids Electrona antarctica and Protomyctophum sp. and the Antarctic krill, Euphausia superba. Information on species composition was the main source of uncertainty in the density estimates, highlighting the need for more biological sampling. This study demonstrates that it is possible to integrate acoustic data collected opportunistically with auxiliary information from research voyages and literature to provide estimates of mesopelagic fish biomass in remote areas. [ABSTRACT FROM AUTHOR]

Parasites manipulating their host to facilitate trophic transmission is a widespread and diverse phenomenon. Trematode eye‐flukes in the family Diplostomidae infect a variety of fish species as metacercariae, many residing in the eyes. A recently described diplostomid, Tylodelphys darbyi, from the South Island of New Zealand has been found to infect common bully Gobiomorphus cotidianus, an endemic freshwater fish. Within the fish, the metacercariae move about freely in the liquid parts of the eye and are quite large. We hypothesized that increasing intensity of T. darbyi infection will result in increasing visual impairment, thus reducing the ability of G. cotidianus to identify and react to a predatory threat. To test this hypothesis, we performed experiments to (a) examine the fish's reaction to a purely visual predator cue and (b) test their ability to avoid simulated predation under natural levels of infection. Among the 64 fish used in our experiments, T. darbyi had a prevalence of 98.7% with an average of 17.6 worms per fish. However, there was no relationship between T. darbyi intensity and either the fish's reaction to a visual predator stimulus or their ability to escape a simulated predator. Our findings indicate that despite being present in large numbers in the eyes of its fish host, the parasite appears incapable of improving its chances of trophic transmission to its avian definitive host. The results also suggest that the fish G. cotidianus could be using other senses (e.g., olfaction and lateral line) to compensate for visual impairment, and detect and respond to predators. [ABSTRACT FROM AUTHOR]

Length–weight relationships are a fundamental tool for assessing populations and communities in fisheries science. Many researchers have collected length–weight data throughout New Zealand, yet parameters describing these relationships remain unpublished for many species of freshwater fish. We compiled 285,124 fish records from researchers and institutions across New Zealand to parameterise length–weight equations, using both power and quadratic models, for 53 freshwater species belonging to 13 families. The influence of location and sex on length–weight relationships was also assessed. Location, in particular, generated different length–weight relationships for 65% of the species examined. Length–weight equations were validated by comparing predicted weights against independently measured weights from 25 electrofished sites across New Zealand and the equations were highly accurate (R2>0.99). Recommendations are made about how to robustly apply this new resource which should assist freshwater fisheries researchers throughout New Zealand. [ABSTRACT FROM PUBLISHER]

The Leigh Marine Laboratory (LML) has taken full advantage of its location on the shores of one of the world's first no-take marine reserves. The foresight of the founders of the laboratory has enabled the pursuit of ecological studies that have been amongst the first to demonstrate the effectiveness of reserves as a tool for conservation and restoration. The insights flowing from this work at Leigh are important, not only for targeted marine species, but also at the ecosystem level, and have proven to be highly relevant to broader resource management issues. Novel methodologies have been employed in the pursuit of these aims, helping to popularise their wider use. More recent work has focused on understanding the processes underlying the variability in response to marine conservation in marine reserves across the spectrum of coastal marine habitats in New Zealand. The LML has probably exceeded the expectations of its founders, who hoped the laboratory might generate information of interest in the fields of ‘resource management, food web dynamics and natural fluctuations distinct from man-induced changes’, and its contribution in the field of marine conservation has been significant both within New Zealand and internationally. This has been a 50-year journey that has gone from a focus on local effects of conservation to the broader context, from direct effects of protection to indirect effects, and from small-scale spatial conservation management to ecosystem-based management. [ABSTRACT FROM AUTHOR]

1. Within-species phenotypic variation is hugely variable and may play a role in determining the range of habitats a species can exploit. Our study addressed two main questions: 1. does phenotypic variation allow some species (i.e. habitat-generalists) to use heterogeneous habitats and 2. are habitat-generalists more variable than species occupying relatively homogeneous environments (i.e. habitat-specialists)? 2. We examined the morphology of the common bully ( Gobiomorphus cotidianus), a habitat-generalist eleotrid fish found in lakes and rivers throughout New Zealand. We also compared the level of morphological variability in common bullies with that in the closely related redfin bully ( Gobiomorphus huttoni), a habitat-specialist of moderate- and fast-flowing rivers. 3. Common and redfin bullies were collected from the South Island of New Zealand. A series of body and fin measurements were made, and cephalic dorsal head pores of the mechanosensory lateral-line system were counted. The pores and associated canal neuromasts are important for prey detection and predator avoidance in other species, particularly, in turbulent conditions where the effectiveness of superficial neuromasts may be compromised. 4. The common bully had more dorsal head pores in fish from rivers than in those from lakes. This pattern was apparent only in adults, suggesting that selective pressures associated with adult habitat, be it rivers or lakes, are responsible. 5. As expected, there was greater phenotypic variability in the generalist common bully than in the specialist redfin bully, particularly with regard to the sensory pores, suggesting their importance for survival in turbulence. 6. We identified habitat-related patterns in phenotypic variability in a generalist species and demonstrated a link between phenotypic variability and habitat breadth. Variation in the common bully may explain its ability to occupy a range of habitats. [ABSTRACT FROM AUTHOR]

Dams are important structures for generating electricity and irrigation, but they often severely modify river hydrology and geomorphology and thus impact freshwater communities. These effects are broadly predictable and therefore, at a catchment scale, biological communities should respond in some predictable manner. We interrogated the New Zealand Freshwater Fish Database to determine whether dams have predictable catchment-scale effects on fish assemblages. Seven selection criteria were applied to over 2000 dams, resulting in 30 dams being considered suitable for analysis. Comparisons were made above and below dams and with data from undammed sites which showed that community composition was significantly different above and below dams. Sites above dams had lower species richness, a lower percentage of diadromous species and a higher percentage of exotic species compared to below dams. None of these differences were present at undammed sites. In summary, dams restrict the movement of diadromous fish generally resulting in their reduction or loss from above-dam habitats and also create artificial lentic ecosystems that exotic species can successively exploit. These changes to fish communities were found across New Zealand and should be viewed as a general consequence of any new dam construction unless fish management and conservation measures are undertaken. [ABSTRACT FROM PUBLISHER]

The diets of red cod Pseudophycis bachus and sea perch Helicolenus percoides were determined from examination of stomach contents of 246 and 494 specimens, respectively, sampled by bottom trawl on Chatham Rise to the east of South Island, New Zealand. The distributions of both species on Chatham Rise overlapped geographically and by depth; the entire P. bachus distribution was encompassed by the H. percoides distribution. The diets of both species were dominated by crustaceans, but fish was also an important dietary component for P. bachus, while pelagic tunicates were important for H. percoides. Despite the overlap in spatial distribution, P. bachus and H. percoides had distinct diets with non-significant overlap, which will markedly reduce resource competition between these two species. The most important crustacean prey were Galatheidae (Munida sp.) and the pandalid shrimp Notopandalus magnoculus in P. bachus, and two-spined crab (Pycnoplax victoriensis) and isopods in H. percoides. Within-species variation in diet was influenced by predator location and ontogeny. The main ontogenetic shifts in diet were from small shrimps to larger fish prey for P. bachus, and from small crustaceans (mysids and galatheids) to larger crustaceans (scampi and crabs) for H. percoides. [ABSTRACT FROM AUTHOR]

Single reaches in three lowland streams in Canterbury, New Zealand, were enclosed with stop-nets and fish removed by repeated electric fishing passes through the day and following night during base flow conditions in late summer. The proportion of fish caught in each pass varied between species and increased with fish size. Electric fishing efficiency declined in the second and third daytime passes, to 0.73 and 0.79 of the first pass respectively, but increased in the first and second night-time passes to 1.87 and 2.02. Population estimates, based on the first two or three daytime passes, accounted for only 62% and 82% of the population estimated using all five day and night passes. A high percentage of small benthic species remained hidden within the substrate during the day but emerged at night and became more vulnerable to electric fishing. Single or multiple daytime passes can be used to estimate the approximate density of most native fish species and size classes in small lowland streams and rivers provided calculations take into account fish hidden within the substrate and marginal vegetation. [ABSTRACT FROM AUTHOR]

The article examines the trace element signatures of juvenile trout otoliths from natal tributaries of the Motueka River catchment, New Zealand. It determines the trace elements using laser ablation inductively coupled plasma mass spectrometry, and differentiated using linear discriminant function analysis. It investigates the temporal stability in element:Ca ratios by repeat collections in juvenile fish.

The article offers information on the study that focuses on the microhabitat use of a native New Zealand galaxiid fish, Galaxias fasciatus. It highlights the materials and methods used in the study including microhabitat use and availability, and data analysis. It also presents the results derived from the study with respect to fish frequency distribution, microhabitat occupied, and habitat availability.

The article focuses on the study on the monitoring of a New Zealand freshwater fish community through the use of passive integrated transponder (PIT) technology. It highlights the methods employed by the research including the site which is the Mangaore stream, western tributary of the Manawatu River, New Zealand.

Feeding habits of the four most abundant deep-sea demersal trawl-caught macrourids on Chatham Rise, New Zealand, were examined from stomach contents. Two species were predominantly benthic foragers: Coelorinchus bollonsi on infaunal and epifaunal polychaetes, and C. aspercephalus on epifaunal crustaceans; and two species were predominantly mesopelagic foragers; C. oliverianus on calanoid copepods, and Lepidorhynchus denticulatus on mesopelagic crustaceans. The most important predictors of diet variability were identified using distance-based linear models and included areal predictors in all four species, fish size in C. aspercephalus, C. bollonsi and L. denticulatus, and sample year in C. bollonsi. Cluster analyses showed that the diets of C. aspercephalus and C. bollonsi were most distinct. There was a greater interspecific similarity in diet in the spatial and fish size subgroups of C. oliverianus and L. denticulatus, than at the species level. Failing to account for areal, temporal, and ontogenetic variability in diets may bias evaluations of resource competition. [ABSTRACT FROM AUTHOR]

The article reports on a study conducted on the diet of lookdown dory, Cyttus traversi, in New Zealand. It is mentioned that examination of stomach content of around 240 specimens of varying lengths, taken from varying depths from Chatham Rise, was conducted. The diet mainly consisted of macrourid fish, natant decapods and galatheid. A multivariate analysis was conducted and four ontogenic units were established namely pelagic, juveniles, maturing males and females and matured females.

The diet of the alfonsino Beryx splendens was determined from examination of stomach contents of 287 specimens of 17 to 48 cm fork length ( LF) sampled by bottom trawl on the Chatham Rise to the east of New Zealand. Prey items were predominantly crustaceans and mesopelagic fishes. The most important prey species by mass was Sergestes spp. prawns, followed by the myctophid Lampanyctodes hectoris, and then Pasiphaea spp. prawns. Multivariate analyses indicated that small crustaceans (euphausiids and amphipods) were most important in the diet of smaller B. splendens (100-424 g, 17-26·5 cm), with larger prawn species and mesopelagic fishes most important for larger fish (425-2070 g, 27-46 cm). Moon phase and bottom temperature also explained some of the variability in diet, but the moon phase effect was difficult to explain, and the bottom temperature effect may have been confounded, to some extent, with LF. The results indicated that B. splendens were moderately selective feeders that foraged primarily in the mesopelagic layers. The diet of New Zealand B. splendens is generally similar to those reported from other areas, i.e. dominated by mesopelagic crustaceans and fishes, and with a transition from small crustaceans to fishes with increasing predator size. [ABSTRACT FROM AUTHOR]

1. Animal malformations engender wide public and scientific concern because of associated environmental health risks. This is highlighted by increased incidence of limb malformations in amphibians associated with trematode infections and disturbance. Malformations may signal new emerging disease threats, but whether the phenomenon is broadly applicable across taxa, or has population-scale impacts, is unknown. 2. Malformations are widely reported in fish and, until now, have been attributed mainly to contaminants. We tested whether the trematode Telogaster opisthorchis caused severe malformations, leading to population effects, in Galaxias anomalus, a threatened New Zealand freshwater fish. 3. Experimental infection of larval fish caused increasing spinal malformation and mortality with infection intensity that closely matched field patterns. Field malformation frequency peaked in January (65%), before declining sharply in February (25%) and remaining low thereafter. 4. The peak occurred during a ‘critical window’ of larval development, with the decline coincident with a population crash, indicating that malformation was causing mortality in the field. 5. The occurrence of such critical developmental windows may explain why this mechanism of population impact has been overlooked. With global environmental stressors predicted to enhance trematode infections, our results show that parasite-induced malformation, and its population-scale impacts, could be more widespread than previously considered. [ABSTRACT FROM AUTHOR]

1. It is well recognised that non-indigenous species (NIS) can affect native communities via the ‘spillover’ of introduced parasites. However, two other potentially important processes, the ‘spillback’ of native parasites from a competent NIS host, where the latter acts as a reservoir leading to amplified infection in native hosts, and the ‘dilution’ of parasitism by a NIS host acting as a sink for native parasites, have either not been tested or largely overlooked. 2. We surveyed the helminth parasite fauna of native New Zealand fish in Otago streams that varied in the abundance of introduced brown trout Salmo trutta, to look for evidence of spillback and/or dilution. Spillover is not an issue in this system, with trout introduced as parasite-free eggs. 3. Seven native parasite species were present across 12 sites; significant inverse relationships with an index of trout abundance (i.e. dilution) were documented for three species infecting the native upland bully Gobiomorphus breviceps, and one species infecting the native roundhead galaxias Galaxias anomalus. 4. An inverse relationship between bully energy status and infection intensity of one parasite species suggests that parasite dilution could have positive effects on bully populations. Our failure to detect similar relationships for the other parasites does not preclude the possibility that dilution is beneficial to native fish, since parasites may have subtle or unmeasured impacts. 5. The parasite dilution patterns reported are compelling in that they occurred across several native host and parasite species; as such they have important implications for invasion ecology, providing an interesting contrast to the largely negative impacts reported for NIS. Mechanisms potentially responsible for the patterns observed are discussed. [ABSTRACT FROM AUTHOR]

Dunn, M. R., Rickard, G. J., Sutton, P. J. H., and Doonan, I. J. 2009. Nursery grounds of the orange roughy around New Zealand. – ICES Journal of Marine Science, 66: 871–885. The orange roughy (Hoplostethus atlanticus) is a deep-sea species with a centenarian lifespan, a life-history feature that may enable the stocks to withstand prolonged periods of recruitment failure. Most stocks have been substantially depleted, however, so estimating recruitment has become a priority in setting catch quotas to ensure future sustainability of the fisheries. A description of the nursery grounds of the species off New Zealand is provided, using extensive research-survey data from 12 541 bottom trawls and 713 midwater trawls. The juveniles were initially caught on the seabed, near known spawning grounds, and towards the shallower end of the species' distribution, and not in midwater or the shallower or deeper bottom tows. Densities were greatest at 850-900 m. As juveniles grew, their spatial and depth distribution expanded, both shallower and deeper, with a skew towards deeper water, such that by the onset of maturation, densities were relatively high in 850–1300 m of water. The early nursery grounds were in relatively warm water, but on the south Chatham Rise, appeared to be bounded by the presence of a cold-water front. [ABSTRACT FROM PUBLISHER]