Blue Warehou Research Articles

Modelling perspective on the climate footprint in south east Australian marine waters and its fisheries

Abstract South eastern Australia is a global warming hotspot, and is also home to ~70% of Australia’s population and one of Australia’s largest fisheries—the South East Scalefish and Shark Fishery. This fishery spans shelf to deep waters, subtropical to temperate waters, employs many gears, and interacts with over 100 species. Despite following best practice fisheries management principles, including taking an ecosystem perspective to overall fisheries interactions, management interventions have failed to arrest or recover the decline of some focal species. Using an Atlantis ecosystem model developed for the fishery over the past 20 years, this paper presents simulations that suggest climate change may be a major contributor to the trajectories seen for a number of species—such as jackass morwong (Nemadactylus macropterus), blue warehou (Seriolella brama), and gemfish (Rexea solandri). This kind of climate influence poses many challenges for fisheries management into the future, raising questions about what to do when climate change undermines or overrides fisheries management actions and objectives.

Effects of fixatives on stable isotopes of fish muscle tissue: implications for trophic studies on preserved specimens.

Isotopic ecology has been widely used to understand spatial connectivity and trophic interactions in marine systems. However, its potential for monitoring an ecosystem's health and function has been hampered by the lack of consistent sample storage and long-term studies. Preserved specimens from museum collections are a valuable source of tissue for analyses from ancient and pre-modern times, but isotopic signatures are known to be affected by commonly used fixatives. The aim of the present study was to understand the effects of fixatives on isotopic signatures of bulk tissue (δ13 Cm and δ15 Nm ) and amino acids (δ13 CAA and δ15 NAA ) of fish muscle and to provide correction equations for the isotopic shifts. Two specimens of each: blue cod (Parapercis colias), blue warehou (Seriolella brama), and king salmon (Oncorhynchus tschawytscha) were sampled at five locations along their dorsal musculature, at four time periods: (1) fresh, (2) after 1 month preserved in formalin, and after (3) 3 and (4) 12 months fixed in either ethanol or isopropanol. Lipid content was positively correlated with C:N ratio (r²=0.83) and had a significant effect on δ13 C after treatments, but not on δ15 N. C:N ratio (for δ13 Cm ) and percent N (for δ15 Nm ) from preserved specimens contributed to the most parsimonious mixed models, which explained 79% of the variation due to fixation and preservation for δ13 C and 81% for δ15 N. δ13 CAA were generally not affected by fixatives and preservatives, while most δ15 NAA showed different signatures between treatments. δ15 NAA variations did not affect the magnitude of differences between amino acids, allowing scientists to retrieve ecological information (e.g., trophic level) independently of time under preservation. Corrections were applied to the raw data of the experiment, highlighting the importance of δ13 Cm and δ15 Nm correction when fish muscle tissues from wet collections are compared to fresh samples. Our results make it possible to retrieve δ13 Cm , δ15 Nm , δ13 CAA , and δ15 NAA from museum specimens and can be applied to some of the fundamental questions in ecology, such as trophic baseline shifts and changes in community's food web structure through time.

Species identification method for marine products of Seriola and related species

The complete nucleotide sequences of mitochondrial DNA (mtDNA) from four Seriola spp. (S. quinqueradiata, S. lalandi, S. dumerili, and S.rivoliana) were determined with the aim of developing a species identification analysis method for discriminating between commercially important Seriola spp. and other related species. In addition, the nucleotide sequences of the mitochondrial cytochrome b gene (Cytb) from five related but less expensive species in terms of market value (Seriolella brama, S. caerulea, S. punctata, Hyperoglyphejaponica, and Rachycentroncanadum), which are often used as substitutes for Seriola spp., were determined. Restriction enzyme sites were examined by comparing the nucleotide sequences, and species-specific primers were designed for PCR-based restriction fragment length polymorphism (RFLP) analysis. Based on the results of the PCR amplification studies, the four Seriola spp. and the five related species tested could be categorized into three groups according to their PCR product pattern: a 373-bp product from the four Seriola spp., a 513-bp product from three Seriolella spp. and H. japonica, and a 204-bp product from R. canadum. In addition, RFLP analysis of the PCR products was able to differentiate these fish species.

Optical properties of raw and processed fish roes from six commercial New Zealand species

This study characterized colour parameters [lightness ( L ∗), redness ( a ∗), yellowness ( b ∗), chroma ( C ∗) and hue ( h ∗)] and spectral surface reflectance of raw and processed roes from the following species: chinook salmon, hoki, southern blue whiting (SBW), hake, blue warehou and barracouta. The roes were processed as karasumi-like at room temperature and as karashi mentaiko at room temperature and at 5 °C. Salmon roe had the highest a ∗-values ( P < 0.01). Karasumi-like products had lower ( P < 0.01) L ∗-values compared with raw roes. Apart from hake, roes with intense pigments (e.g. salmon and warehou) had lower a ∗-values after karasumi-like processing. Karashi mentaiko processing increased ( P < 0.01) a ∗-values of roes that had white or translucent background (e.g. barracouta, hoki, and SBW) to a greater extent than those that had yellow/orange background (hake and warehou). Redness ( a ∗-value) was the major contributor in the separation of different products by canonical analysis. Spectral reflectance of the surface echoed the differences found among the raw roes from different fish species and the impact of processing on the colour of the final products. It is important to determine what influence these colours have on consumer preference.

An opportunistic detection of amoebic gill disease in blue warehou, Seriolella brama Günther, collected from an Atlantic salmon, Salmo salar L., production cage in south eastern Tasmania

Amoebic gill disease (AGD) is a recurrent health issue affecting the commercial culture of Atlantic salmon, Salmo salar L., in south eastern Tasmania

Effect of Processing Conditions on Trace Elements in Fish Roe from Six Commercial New Zealand Fish Species

The concentrations of trace elements in fish roes and the effect of processing conditions (karasumi-like or karashi mentaiko) were investigated in six commercial fish species from New Zealand. The studied elements were As, Cd, Cr, Cu, Hg, Pb, and Zn, and the roes were from the following species: chinook salmon ( Oncorhynchus tshawytscha), hoki ( Macruronus novaezelandiae), southern blue whiting ( Micromesistius australis), hake ( Merluccius australis), blue warehou ( Seriolella brama), and barracouta ( Thyrsites atun). The concentrations of As, Cd, Cr, Hg, and Pb in the roes were lower than literature values for fish muscles. Only Zn in barracouta roe and Cu in salmon roe and their products were relatively higher than the generally accepted levels in fish muscles and could be of safety concern. Hence, the consumption of barracouta and salmon roes among certain parts of the population needs to be monitored and assessed. Dry salting (karasumi-like) processing increased ( P < 0.001) the concentrations of the studied trace elements while salting fermentation (karashi mentaiko) processing tended to decrease the levels of trace elements. Fermentation may be a useful process to decrease the level of toxic trace elements.

Genetic stock structure of blue-eye trevalla (Hyperoglyphe antarctica) and warehous (Seriolella brama and Seriolella punctata) in south-eastern Australian waters

Blue-eye trevalla (Hyperoglyphe antarctica), blue warehou (Seriolella brama) and silver warehou (Seriolella punctata) from the family Centrolophidae are three commercially important species in the Australian fishery. These species are currently managed as single stocks. We tested the hypothesis that patterns of phenotypic structuring in these species reflect underlying genetic stock structure using an analysis of mitochondrial DNA control region sequences. The analysis revealed high levels of haplotype diversity within populations. The most common haplotypes for the species occurred in all geographical locations sampled. For S. brama, although structuring was not significant after Bonferroni correction, differences between two sites were sufficient to warrant caution in the management of fishery zones for this species. There were also some indications of structuring when sites were grouped into common regions. Demographic analysis suggested that S. brama might have had a history of population bottlenecks followed by sudden population expansion, potentially contributing to genetic structuring in the fishery. No structuring was detected for H. antarctica and S. punctata. The present study highlights the need for, and the utility of, multiple sources of information, that is, genetic, phenotypic, behavioural and ecological, when managing marine fisheries and the need to take a cautionary approach to the interpretation of genetic data for fisheries management.

Including discard data in fisheries stock assessments: Two case studies from south-eastern Australia

Discarding of target species can be substantial in some fisheries. For fisheries managed using Total Allowable Catches, such as Australia's Southern and Eastern Scalefish and Shark Fishery (SESSF), discarding of target species can occur for reasons related to the size of the fish caught, markets, and the amount of quota held by individual quota holders. This paper illustrates how the assessments for two of the species in the SESSF, blue grenadier, Macruronus novaezelandiae, and the western stock of blue warehou, Seriolella brama, are conducted to take account of discards. Discards of blue grenadier are predominantly small fish so the assessment distinguishes between retained and discarded fish, and includes likelihood components related to the weight of the discards and the age-structure of the discards. In contrast, discards of blue warehou are due primarily to quota-related issues, so the assessment adds the discards to the catches and the catch-rate indices, and fits to total catches and catch-rates. Model outputs suggest that strong year-classes can be detected before they enter the fishery by including data on discards in assessments while ignoring such data when conducting assessments can lead to biased assessment outcomes. Several caveats related to the use of data on discards in stock assessments are outlined.

The diet of Little Penguins (Eudyptula minor) at Phillip Island, Victoria, in the absence of a major prey—Pilchard (Sardinops sagax)

The diet of Little Penguins (Eudyptula minor) was investigated in December 1995 and during the 1996–97 breeding period at Phillip Island, Victoria, Australia. The composition of the diet in this study differed markedly from that reported previously. Pilchard (Sardinops sagax), once a major prey, had virtually disappeared from the diet and Anchovy (Engraulis australis) showed a substantial decrease in frequency of occurrence. Instead, penguins had taken a temporal succession of juveniles of Red Cod (Pseudophycis bachus), Barracouta (Thyrsites atun), and Blue Warehou (Seriolella brama). Little Penguins had lower and higher than average breeding success in the 1995–96 and 1996–97, respectively, suggesting that the absence of Pilchards itself did not necessarily reduce the breeding success of Little Penguins. These findings contrast with those recorded in the 1980s when the absences of Pilchard and Anchovy had a negative impact on the penguins’ breeding performance.

Larval distribution and abundance of blue and spotted warehous (Seriolella brama and S. punctata: Centrolophidae) in south-eastern Australia

The early life histories of the commercially important blue and spotted warehous (Seriolella brama and S. punctata) were examined on the basis of archived ichthyoplankton samples collected over broad areas of southern Australia. Larvae of both species were widely distributed during winter and spring within shelf and slope waters. Larvae of S. brama were recorded from Kangaroo Island, South Australia (SA), to southern New South Wales (NSW). Seriolella punctata larvae were recorded from western Tasmania to southern NSW. Back-calculated spawning dates, based on otolith microstructure, indicated that spawning predominantly occurs during late July and August but that the timing of spawning varies between regions. The abundances of small larvae (&lt;5. 0 mm body length) were highest for both species off western Tasmania and southern NSW. No small S. brama larvae were recorded between southern Tasmania and southern NSW, whereas low but consistent numbers of small S. punctata larvae were found between these regions. The data suggest that there are separate spawning areas for S. brama in western and eastern regions of Australia’s South East Fishery. The pattern for S. punctata is less clear, but suggests a more continuous link among populations in south-eastern Australia.

Validated ageing methods for blue warehou (Seriolella brama) and white warehou (S. caerulea) in New Zealand waters

Blue warehou (Seriolella brama) and white warehou (Seriolella caerulea) (Stromateoidei : Centrolophidae) from New Zealand waters were aged from counts of zones in cross-sectioned otoliths, a technique that was validated for both species by examining the state of otolith margins from fish sampled regularly throughout the year. Von Bertalanffy parameters were calculated for blue warehou on the Stewart-Snares shelf. The fish grew rapidly up to the time of first spawning (~4 –5 years) , but growth was negligible after ~10 –12 years. A maximum age of 22 years was recorded. Von Bertalanffy parameters were calculated for white warehou from the Chatham Rise and the Campbell Plateau;there were no significant differences in growth between areas. The fish grew rapidly up to the time of first spawning (~3 –4 years) , but growth was negligible after ~6 –8 years. A maximum age of 21 years was recorded. Females of both species grow significantly faster than males. A revised growth model for silver warehou (Seriolella punctata) is also presented.

Reproductive characteristics and per-recruit analyses of blue warehou (Seriolella brama): implications for the South East Fishery of Australia

Monthly samples of commercial catches of S. brama were collected between May 1996 and December 1997 in three regions of the fishery:off the east coast of Victoria; eastern Tasmania; and western Bass Strait. Sex ratio, gonadosomatic index, macroscopic and histological development, size at maturity and fecundity were estimated and combined with data on growth and mortality to perform per-recruit analyses. The main spawning period was during winter–spring and there was evidence of spawning in each of the three regions. Blue warehou reach maturity at 30–40 cm fork length. They have a determinate annual fecundity and spawn around three batches of eggs during a season. Eggs-per-recruit analyses revealed maximum egg production at ~40 cm (4–5 years) in an unfished population. Gill-net fishing, which targets fish &gt;45 cm, was less likely to affect the relative eggs-per-recruit in a population than trawl fishing, which catches a wider range of smaller fish. These results are discussed in light of the current management arrangements in the fishery and will be used in models to assess the effect of fishing on the long-term sustainability of the blue warehou.

Estimating gill-net selectivity for five species caught in the South East Fishery, Australia

A formal approach to estimating selectivity patterns that allows for variability additional to Poisson sampling variability is outlined. This approach, which involves assuming that the catch of fish by a particular size of gill-net in a given size-class is distributed according to a negative binomial distribution, is applied to data for five of the species caught by experimental gill-nets in Australia’s South East Fishery. The data for two of these species (blue warehou and dogfish) are not compatible with the conventional assumption that the size of fish corresponding to maximum selectivity is linearly proportional to mesh size. Selectivity and population size-structure are found to depend on depth and habitat type for some of the species. It is necessary therefore to target future experiments to depth zones/habitat types in which the bulk of the catch is taken to estimate selectivity patterns for use in stock assessments.

Extinction of marine renewable resources: a demographic analysis

AbstractA simple (deterministic) population dynamics model is used to examine the level of fishing mortality at which a population is expected to be driven to extinction (Fcrash). Values for Fcrash are determined for six marine fish species (Cape hake, blue grenadier, blue warehou, school shark, gummy shark, and orange roughy) subject to commercial harvest. The sensitivity of the value of Fcrash to changing the selectivity pattern of the fishery and the relationship between the size of the reproductive component of the population and subsequent births to allow for depensatory effects is examined. Fcrash is greatest for highly productive species and when the fishery does not target immature animals. The ratio of Fcrash to the fishing mortality at which maximum sustainable yield is achieved, FMSY, is a decreasing function of the productivity of the population. The possibility of depensation has little impact on FMSY but can substantially reduce the ratio Fcrash/FMSY. A series of stochastic simulations is conducted to assess the probability of detecting that the extent of fishing exceeds Fcrash using the current IUCN A criterion. The results of these simulations are also used to determine the probability that the IUCN A criteria will be triggered when fishing takes place at FMSY. The results indicate that there are substantial probabilities of incorrectly identifying species being harvested at FMSY as being threatened during the ‘fishing down’ phase and also of not identifying species actually at risk of extinction if fishing mortality is not reduced.