Food of predatory demersal fish in Hauraki Gulf

Feeding was examined in five species of fish associated with snapper Chrysophrys auratus (Forster) trawled from Hauraki Gulf and north‐west Bay of Plenty: trevally Caranx lutescens Richardson, red gurnard Chelidonichthys kumu Lesson and Garnot, horse mackerel Trachurus novaezelandiae Richardson, eagle ray Holorhinus tenuicaudatus (Hector), and john dory Zeus japnnicus Cuvier and Valenciennes. All five species feed on some elements of the bottom fauna; in general, crustaceans were the most important food group.     

Snapper (Chrysophrys auratus): a review of life history and key vulnerabilities in New Zealand

Snapper (Chrysophrys auratus) is an important coastal fish species in New Zealand for a variety of reasons, but the large amount of research conducted on snapper has not been reviewed. Here, we review life history information and potential threats for snapper in New Zealand. We present information on snapper life history, defining stages (eggs and larvae, juvenile and adult), and assess potential threats and knowledge gaps. Overall we identify six key points: 1. post-settlement snapper are highly associated with certain estuarine habitats that are under threat from land-based stressors. This may serve as a bottleneck for snapper populations; 2. the largest knowledge gaps relate to the eggs and larvae. Additional knowledge may help to anticipate the effects of climate change, which will likely have the greatest influence on these early life stages; 3. ocean acidification, from land-based sources and from climate change, may be an important threat to larval snapper; 4. a greater understanding of population connectivity would improve certainty around the sustainability of fishery exploitation; 5. the collateral effects of fishing are likely to be relevant to fishery productivity, ecosystem integrity and enduser value; 6. our understanding of the interrelationships between snapper and other ecosystem components is still deficient.     

Food of snapper in western Bay of Plenty,New Zealand

Feeding was examined in 772 snapper, Chrysophrys auratus (Bloch and Schneider), from the western Bay of Plenty, New Zealand. Occurrence, points (bulk), and numbers methods of food analysis were used in the study. Diet was extremely varied, and, by all methods of food analysis, crustaceans, polychaetes, echinoderms, molluscs, and teleosts formed the main snapper food groups, with crustaceans being the most important. Size of snapper, depth, sampling area, and time of day affected the occurrence, volume, and numbers of food items, while sex did not.

Seasonal feeding patterns on most species/categories of food varied locally within each sampling area, and there were no uniform seasonal feeding patterns for any food/category in the four sampling areas examined.     

Vertical migration,catchability and acoustic assessment of semi-pelagic Cape horse mackerel Trachurus trachurus capensis in the southern Benguela

The vertical distribution and migration of the Cape horse mackerel Trachurus trachurus capensis were investigated on the basis of midwater and bottom trawl collections taken over diel cycles at two sites on South Africa's south coast. Attempts were also made to investigate the relationship between bottom trawl catch rates and acoustic abundance estimates. During the first cycle, horse mackerel were dispersed in midwater during the night, and towards sunrise they coalesced into schools and migrated to the seabed where they remained throughout the day. During that cycle, horse mackerel did not appear to feed, despite the prevalence of potential food, mainly Calanus copepods and euphausiid larvae, in the water column. In contrast, during the second cycle, horse mackerel remained near the seabed during the 24-h experiment, but they exhibited a marked feeding periodicity, with most feeding taking place in the late afternoon. They appeared to select for larger copepods in the water column. Several reasons are advanced to explain the difference in the vertical migratory behaviour of horse mackerel between the two sites, on the basis of the vertical distribution of their potential prey. Diel differences in acoustic estimates of horse mackerel abundance were significantly reduced after applying an acoustic deadzone correction factor. Trawl catches, however, could not be reconciled with acoustic estimates during the day, when horse mackerel were too close to the bottom for effective echo-integration.     

Influence of oceanographic fronts and low oxygen on the distribution of ichthyoplankton in the Benguela and southern Angola currents

The study focuses on ichthyoplankton populations in the southern Angola Current, the Angola-Benguela Front and the coastal upwelling area of the northern and central Benguela Current. The horizontal and vertical distributions of eggs and larvae of sardine Sardinops sagax, anchovy Engraulis encrasicolus and horse mackerel Trachurus trachurus capensis were examined in relation to distribution patterns of temperature, salinity and dissolved oxygen. Samples were collected during February–March 2002 using a Bongo net and a multiple opening/closing net in five depth layers (0–30m, 30–60m, 60–100m, 100–140m and 140–220m). Eggs and larvae were restricted mainly to the shelf areas in the Angola-Benguela Font and southern Angola Current waters. Their vertical distributions in the Angola-Benguela Front and northern Benguela upwelling region showed a sharp decline in abundance at about 60m depth. This decline appeared to be correlated to the distribution of dissolved oxygen in the water column It is hypothesised that low oxygen concentrations have a strong impact on the development and survival of the early life-cycle stages of fish, and that recruitment of sardine and other pelagic species relies more on the upward extension of the oxygen minimum layer than was previously thought.     

Assessment of a shell bank and associated substrates as nursery habitat of postsettlement red snapper

Trawl surveys were conducted in 2000 and 2001 to examine patterns of distribution and abundance of postsettlement red snapper (Lutjanus campechanus) on a shell bank, Freeport Rocks Bathymetric High (FRBH), in the northwestern Gulf of Mexico. In addition, otolith-based methods were used to determine age, hatch-date, growth and mortality of new recruits associated with FRBH. Date and region were significant factors affecting density of red snapper in 2000. Peak densities of red snapper were observed in July and August, and mean density among habitat types (shell bank, inshore mud, offshore mud) was similar (range: 50–52 ind hectare⁻¹) in 2000. Alternatively, a habitat effect was detected during a limited survey conducted in 2001, with density higher on the shell bank than inshore or offshore mud habitat. Postsettlement red snapper were first detected at approximately 16 mm standard length, and individuals less than 20 mm were present in all habitats. Estimated ages of red snapper ranged from 26 to 121 d, with new settlers (≤20 mm) typically less than 28 d. Predicted hatch dates ranged from early April to mid August with a single peak occurring from late May to early June. Growth rate for the April–May cohort (0.817 mm d⁻¹) was similar to the June–July cohort (0.830 mm d⁻¹). Habitat-specific differences in growth were observed, and rates were highest for individuals from the inshore habitat (0.881 mm d⁻¹). Mortality rates (Z) during the early post-settlement period were approximated using catch curves, and early life mortality of red snapper was 12.1% d⁻¹ (Z=0.129). While the difference in mortality between cohorts was negligible, a habitat-specific difference in mortality was observed. Mortality rate of red snapper inhabiting the inshore mud habitat (Z=0.045, 4.4% d⁻¹) was lower than rates observed for individuals on the shell bank (Z=0.120, 11.9% d⁻¹) or offshore (Z=0.099, 9.3% d⁻¹) habitat. Individuals residing in the inshore habitat had significantly higher growth rates and significantly lower mortality rates, suggesting that recruitment potential was higher for these individuals.     

Variable spatial structure of schooling pelagic fish off Namibia: implications for acoustic surveys

Schools of horse mackerel Trachurus trachurus capensis, sardine Sardinops sagax and round herring Etrumeus whiteheadi were surveyed by conventional echo-integration along systematic transects. The transects were surveyed twice, in opposite directions. Clupeoid biomass was concentrated in a few dense aggregations, whereas horse mackerel were less dense and distributed over larger areas. The influence of aggregation patterns of the different species on the precision of the acoustic estimates was analysed with respect to spatial variability and diurnal effects. Isotropic variograms computed from values of acoustic back-scattering strength showed little or no structure for all three species. Indicator variograms showed relatively large structures (>15 miles) for all three species at the lowest cut-off level, confirming the influence of high values on the variograms. The autocorrelation range decreased with an increase in cut-off value for horse mackerel, whereas variograms of sardine and round herring showed no structure at larger cut-off values. There were large variances in estimated biomass for sardine (77%) and round herring (90%) between surveys, whereas biomass estimates of horse mackerel were relatively similar between surveys.     

Food of snapper,Chrysophrys auratus (forster), in the Hauraki Gulf,New Zealand

The food of the snapper, Chrysophrys auratus (Forster), in the Hauraki Gulf was investigated by an occurrence method. The diet was extremely varied and depended on the size of the fish and the food available to it. Variation in feeding occurred during the day, but there was no difference in diet at different times of the year or between male and female snapper.

No evidence was found for the existence of two races of snapper in the Hauraki Gulf. Changes of colouration and behaviour among snapper schooling in the summer appeared merely to be associated with spawning activity.     

基于个体的东海鲐鱼补充量年际变动模拟研究

东海鲐鱼（Scomber japonicus）是我国近海重要经济鱼种,年际资源量波动较大,物理环境对其资源量的丰歉影响很大。本文运用基于个体的东海鲐鱼生长初期生态模型,模拟1978-2013年东海鲐鱼资源补充量。模拟发现,物理环境的变化确实能导致东海鲐鱼资源补充量的年际差异,并且在90年代后出现了较大的波动,资源补充量最多的2002年（1.8×109尾）与最少的1996年（6.5×108尾）相差1.15×109尾。产卵后的15~30 d,即4月份鱼卵仔鱼所处的海洋物理环境对东海鲐鱼最终的资源补充量起到重要作用,4月底鱼卵仔鱼的存活量基本上决定了东海鲐鱼最终的资源补充量的多寡。4月份的水温是影响鲐鱼资源补充量的物理因素之一,4月份水温高有利于提高鲐鱼的资源补充量,相反,水温偏低不利于鲐鱼的资源补充量。4月份的台湾暖流的流速也是影响鲐鱼资源补充量的另外一个物理因素,4月份台湾暖流的势力强对东海鲐鱼最终资源补充量是有利的,相反,流速小对补充量较不利。4月份台湾暖流的水温、流速决定最终东海鲐鱼资源补充量。     

Population genetic studies of horse mackerel Trachurus trecae and Trachurus trachurus capensis off Angola

Genetic variability of the Kunene horse mackerel Trachurus trecae and the Cape horse mackerel Trachurus trachurus capensis was examined using starch gel electrophoresis of enzymatic proteins on individuals collected along the Angolan coast. Six polymorphic enzyme loci were found in both species. The idh-2* locus displayed differences between the two species, and several alleles at different loci exhibited different allele frequencies between the two species, indicating that they are genetically different. Significant differences found in the distribution of allele frequencies between Kunene horse mackerel from the Benguela region of Angola indicated that this species consist of more than one randomly mating population in Angolan waters.     

The influence of habitat structure on juvenile fish in a New Zealand estuary

Estuarine and sheltered coastal habitats that contain physical structure are potentially important nurseries for juvenile fish. Many of these structured habitats, however, are potentially vulnerable to stressors such as elevated turbidity. Quantifying the benefits that structured habitats provide to juvenile fish may therefore be an important step in the management process. We investigated the value of structured habitat for juvenile fishes in northeastern New Zealand, using artificial seagrass units (ASUs) with varying blade density. ASUs were predominantly settled by juvenile snapper (Pagrus auratus) and spotty (Notolabrus celidotus). The density of both snapper and spotty was greatest on ASUs with the highest blade density. For snapper, a gradient in abundance was present (with higher abundance closer to the harbour mouth), suggesting either a gradient in the supply of recruits or a potential recruitment shadow effect. The size distribution of juvenile snapper (12–70 mm fork length) was very similar on both sampling trips, despite the 2‐month interim period, suggesting an ontogenetic habitat shift dependent on size. The condition of juvenile snapper from ASUs with the highest blade density was also greater than the other ASU treatments. Overall, these results provide new empirical evidence that habitats with physical structure within shallow estuarine systems are important to early stage juvenile fishes such as snapper, and indicate that the location‐specific context of that habitat is also likely important.     

Distribution and growth of snapper Chrysophrys auratus in the North Taranaki Bight,and management implications of these data

A bottom trawl survey was used to determine the position of a nursery ground for snapper, Chrysophrys auratus, in the North Taranaki Bight, New Zealand, and so indicate what area should be protected from potentially harmful fishing techniques. A nursery ground for trevally, Caranx georgianus, was also identified. The growth rate of snapper from the North Taranaki Bight is shown to be much faster than Hauraki Gulf and East Cape stocks, but quite similar to Tasman Bay fish. The onset of sexual maturity appears to be related to fish size rather than age, with about 80% of snapper being mature at a fork length of 25 cm. Recruitment success varies greatly between years, and successful recruitment may be related to warm spring temperatures.     

Evidence for long‐term site fidelity of snapper (Pagrus auratus) within a marine reserve

Increases in the density of exploited species on unfished reefs logically implies that some individuals are at least temporarily resident, or show fidelity to a particular area. We tagged snapper (Pagrus auratus (Bloch & Schneider 1801)) in the Leigh Marine Reserve, New Zealand using visible implant fluorescent elastomer tags, recoverable by diver visual sightings without the need to recapture the fish. Batch tagging of snapper (n = 907) was done during an angling survey in June and December 1996, and individually coded tags were implanted by divers (n = 117) in January 1999. Snapper tagged during both programmes were recovered on irregular intervals from 1997 to 2000. There were 71 recoveries of batch tags within 500 m of their tagging sites, and these recoveries were still being made >3 years after tagging: Of individually coded fish, 49 (42%) were seen, sometimes repeatedly over several months, close to their respective tagging sites. These observations included snapper as small as 23 cm fork length, contradicting the commonly held impression that only large snapper take up long‐term residency on reefs. This preliminary evidence suggests that some snapper exhibit site fidelity to areas only a few hundred metres wide, and in the absence of fishing may occupy the same area for years.     

Barium variation in Pagrus auratus (Sparidae) otoliths: A potential indicator of migration between an embayment and ocean waters in south-eastern Australia

Chronological variation in otolith chemistry can be used to reconstruct migration histories of fish. The use of otolith chemistry to study migration, however, requires knowledge of relationships between the chemical properties of the water and elemental incorporation into otoliths, and how water chemistry varies in space and time. We explored the potential for otolith chemistry of snapper, Pagrus auratus, to provide information on movement history between a large semi-enclosed bay, Port Phillip, and coastal waters in south-eastern Australia. Comparisons of water chemistry across two years demonstrated that ambient barium (Ba) levels in Port Phillip Bay were approximately double those in coastal waters (11 μg L⁻¹ versus 6 μg L⁻¹). Ba levels in otolith margins of wild juvenile snapper were highly positively correlated with ambient levels across 17 sampling locations, and levels in otolith margins of adult snapper collected from Port Phillip Bay were approximately double those of snapper collected in coastal waters. Mean partition coefficients for Ba (D_Ba) were similar for juvenile (0.43) and adult (0.46) otoliths, suggesting that otolith Ba incorporation relative to ambient levels was similar across life-stages. Low Ba variation across otoliths from adult snapper maintained in tanks for three years indicated that annual temperature and/or growth cycles did not strongly influence otolith Ba variation. We concluded that chronological Ba variation in snapper otoliths would be a reliable proxy for life-history exposure to variable ambient Ba. We used water chemistry data and Ba levels across otoliths of ocean resident snapper to estimate otolith Ba levels indicative of residence in Port Phillip Bay (>10 μg g⁻¹) or coastal waters (<6 μg g⁻¹). Peaks in Ba exceeding 10 μg g⁻¹ were common across otoliths of snapper collected in Port Phillip Bay and a nearby coastal region. The location of strong Ba peaks within otoliths was consistent with residence in Port Phillip Bay during the spring/summer when snapper move into the Bay from coastal waters to spawn. Our results for snapper support the use of otolith Ba as a proxy for ambient levels throughout the life-history, however, confident interpretation of migration history from otolith Ba chronologies will most likely require matching time series of ambient Ba in the water bodies of interest.     

Food of predatory demersal fish in Hauraki Gulf

Feeding was examined in 1,194 snapper, Chrysophrys auratus (Forster), from Hauraki Gulf and north‐west Bay of Plenty. Occurrence and points (bulk) methods of food analysis were used in this study. By occurrence and bulk, crustaceans, polychaetes, echinoderms, molluscs, and teleosts formed the main snapper food groups, with crustaceans being the most important. Size of snapper, bottom type, depth, time of day and geographical regions affected the occurrence and importance of food items, while sex of fish probably did not.     

Stock assessment and management implications of horse mackerel (Trachurus japonicus) in Korean waters, based on the relationships between recruitment and the ocean environment

This study presents an example of horse mackerel (Trachurus japonicus) stock to demonstrate that marine environmental factors are important in stock assessment for the new Korean Total Allowable Catch (TAC)-based fisheries management system. The estimated survival rate (S) of horse mackerel ranged from 0.25 to 0.36. The instantaneous coefficient of natural mortality (M) was 0.48/year, and the age at first capture was 0.83 year. Annual biomass of horse mackerel in Korean waters was estimated by a biomass-based cohort analysis using annual catch in weight at age during 1965–1995. Yield-per-recruit and spawning biomass-per-recruit were estimated under various harvest strategies at F_max, F_0.1, F_30% and F_40%. A method for estimating acceptable biological catch (ABC) is proposed for dealing with the large differences in the quality and quantity of information and data available. Using recruitment of horse mackerel estimated from various spawner–recruitment relationship models combined with salinity, volume transport, and zooplankton biomass as environmental factors, the ABC under the best information available was estimated to range from 3100 to 3800 mt.     

Horse mackerel egg identification using DNA methodology

Egg identification in plankton samples is usually needed for purposes of stock assessment. Until recently, only morphological characters were used for identifying the eggs of different fish species. Late developmental stages are easily distinguishable due to pigmentation as well as egg and oil globule size range. However, for early stages, these characteristics are difficult to be discriminated and may overlap with other species. European horse mackerel species (Trachurus trachurus, T. mediterraneus, T. picturatus) overlap significantly in their spawning areas in some European waters. Because of the fact that their eggs are morphologically similar, genetic methodologies are needed to identify eggs and larvae to species correctly. In the present study, formalin‐ and ethanol‐preserved eggs were tested to estimate the efficacy of genetic methodologies for species identification of eggs when different preservatives are used. A 370‐bp fragment of cytochrome b was successfully amplified followed by restriction fragment analysis with two restriction enzymes aiming to identify the eggs to species. Horse mackerel egg identification was accomplished with the maximum success in ethanol‐preserved eggs. However, it seems that various preservatives had different effects on the DNA quality of eggs as genetic identification was less successful in formalin‐preserved eggs. Preserving in ethanol a part of the eggs obtained in plankton surveys is suggested for purposes of accurate genetic identification, even if their morphological features are distorted in time.     

Comparison of the growth rates of two stocks ot snapper (Chrysophrys auratus) in south‐east Australian waters using capture‐recapture data

Between 1957 and 1962, 4155 snapper, Chrysophrys auratus (Bloch & Schneider), were tagged and released at a number of sites in Victoria. By the end of June 1972, 210 had been recaptured, and knowing their lengths at release and recapture and the periods at liberty, we determined the von Bertalanffy growth parameters K and L ₈ ^. The values (with 95% confidence limits) were: eastern stock ‐ K = 0.071 ± 0.040, L₈ = 968 ± 325 mm; western stock ‐ K = 0.068 ± 0.023, L₈ = 1079 ± 209 mm; combined stocks ‐ K = 0.062 ± 0.019, L ₈ = 1119 ± 215 mm. No difference between the stocks was apparent when we compared the estimates of K and L ₈ separately; however, when the estimates of K and L ₈ were compared together, a Wilcoxon's test gave a significance probability of 1.5%, indicating a difference in growth rate between the stocks. For the range of lengths of snapper recaptured, this difference was evidently caused by faster growth of snapper from the western stock.     

Ichthyoplankton spatial pattern in the inner shelf off Bahía Blanca Estuary, SW Atlantic Ocean

This study focuses on the composition, abundance and distribution of ichthyoplankton in the inner shelf area off Bahía Blanca Estuary on the SW Atlantic Ocean during late spring. Eggs and larvae of Brevoortia aurea, Engraulis anchoita, Parona signata, Sciaenidae spp. – such as Cynoscion guatucupa and Micropogonias furnieri –, and Odontesthes argentinensis were found. Species richness was low probably as a result of season and shallow depths. Ichthyoplankton abundance reached values close to 10 000 per 10 m⁻³ (eggs) and 4000 per 10 m⁻³ (larvae) and displayed a spatial distribution pattern with maximum abundance values restricted to a band parallel to the coast. Differences between egg and larval patterns, probably derived from a different displacement and hydrodynamic behavior, were observed. Egg and larvae distribution patterns were found related with spawning areas and to directly depend on salinity and mesozooplankton. The larvae distribution pattern, in particular, was found to inversely depend on particulate organic carbon. In addition, the geographic location of egg and larvae maxima strongly coincided with a saline front reported for this area in springtime, thus suggesting a direct relationship with it.     

Feeding relationships between Tarakihi and snapper in western Bay of Plenty,New Zealand

Feeding relationships between two predatory demersal fishes, tarakihi Cheilo‐dactylus macroplerus (Bloch & Schneider) and snapper Chrysophrys auratus (Bloch & Schneider), in relation to the benthos were examined at six sampling areas in the western Bay of Plenty during October to December 1969 and April to June 1970.

Food selectivity was determined. The results showed that both fish species positively selected many of the same food categories. The average Food Similarity Index based on volume data was 18.9% and the average number of food categories shared was approximately 60% of the total number of food categories consumed.

The feeding relationships between tarakihi and snapper and the benthos varied with both sampling area and sampling period. Competition for food is probably minimal, since both fish species eat a wide range of foods and feed at different times.