Southern Bluefin Tuna Thunnus Maccoyii Research Articles

Changes in growth of juvenile southern bluefin tuna (Thunnus maccoyii): an analysis of length-frequency data from the Australian fishery

Modal analysis is applied to historical length–frequency records of the Australian southern bluefin tunafishery, in order to quantify the variation in mean length from year to year. In the South Australian fishery in the first half of March, the mean length has ranged between 54 cm and 64 cm for 1-year-old fish, 73 cm and 85 cm for 2-year-old fish, and 85 cm and 100 cm for 3-year-old fish. The mean lengths of 2-, 3- and 4-year-old fish, and the increment from age 1 to age 3, have increased substantially over the history of the fishery. This increase in growth is probably a response to a decline in the population due to heavy fishing. In many years in the Western Australian fishery, two or more groups of 1-year-old fish were found: the mean lengths of these groups typically differed by 10 cm. Growth rates also varied markedly according to the season of the year.

Estimation of tag reporting rates in agestructured multicomponent fisheries where one component has observers

For many tagging experiments, it is vital that fishers find and report all tags to scientists. If not, the tag reporting rate needs to be estimated so that fishing and natural mortality rates can be estimated. One way to estimate this rate is to have one fishery component (e.g., with observers) report every tag found from all fish that it catches. If the numbers of fish caught by all fishery components are also known and the tagged fish are mixed with the population (or subpopulation) being harvested, then one can estimate the reporting rate of underreporting fishery components. This procedure can fail if data are pooled over ages. We obtain maximum likelihood estimators for the reporting rate for each age and (or) each fishery component. We show how to estimate reporting rates if mixing of tagged and untagged fish occurs with some delay. We also obtain overall age-dependent reporting rates, which combine reporting rates from all components of the fishery. Our likelihood is part of an integrated likelihood that allows estimation of age-dependent fishing and natural mortalities in addition to the reporting rates. Our procedures are illustrated with some southern bluefin tuna (Thunnus maccoyii) tagging data.

Correlates of growth in farmed juvenile southern bluefin tuna Thunnus maccoyii (Castelnau)

In developing the mariculture of the southern bluefin tuna, there is a need to reduce handling of large tuna and to be able to assess their recent growth in research and commercial situations. The potential of various indices as correlates of growth and nutritional status was examined in PIT tagged juvenile tuna grown for 133 days. The study focused on the correlations between specific growth rate for wet weight (SGR) or fork length (SGR L) and morphological (condition factor and tissue–somatic indices), physical (muscle temperature) and biochemical (tissue protein, RNA and DNA concentrations) indices. Tuna held in cages were fed twice per day to satiation on one of four feeds (defrosted pilchards, research and two commercial prototypes). Final wet weight, change in wet weight, SGR, SGR L, condition factor and white muscle concentrations of protein, RNA and DNA were all higher for tagged tuna fed pilchards. Irrespective of diet, the white muscle protein, RNA and DNA concentrations and the ratios between them were all significantly and positively related to SGR. Liver protein, RNA and DNA concentration and the protein:DNA ratio were significantly and positively related to SGR. SGR was predicted by condition factor and by muscle temperature and this was reflected by the positive and significant correlations between muscle temperature and biochemical indices from muscle tissue. Regression models best predicted SGR from condition, pyloric caecal somatic index and white muscle RNA concentration and were tested by predicting (known) SGR of tuna grown in the previous year.

Mass Mortality of Captive Southern Bluefin Tuna (Thunnus maccoyii) in April/May 1996 in Boston Bay, South Australia: A Complex Diagnostic Problem.

In April 1996 approximately 75% (1, 700 t) of the captive, southern bluefin tuna Thunnus maccoyii in Boston Bay, South Australia died. Most deaths occurred during the two days, 15 and 16 April. There was a time association with an ocean surge (11-14 April) and strong winds (12-20 knots on 12 and 13 April). Unfortunately, no environmental data such as levels of dissolved oxygen, suspended solids and toxic algae were available for the critical period 11-17 April inclusive and even some of that collected subsequently was not ideal. Clinical signs reported in the affected fish were that they were obviously distressed, swimming in a haphazard fashion at the surface and, in some instances, exhibiting gasping behaviour. On 15 and 16 April dead fish were reported to have large quantities of mucus flowing from their gills. This was not always the case with fish dying later in the episode. Most material available for histopathological examination was autolysed to some extent, but a small number of suitable samples revealed swelling of the respiratory epithelial cells and subepithelial oedema of the secondary lamellae. Possible aetiological factors responsible for the episode, either alone of in concert, were considered to be microalgal toxicosis, hypoxia, smothering by suspended solids and hydrogen sulphide toxicity. These are discussed in relation to the oceanography of Boston Bay and the unique anatomical and physiological characteristics of tuna.

Population dynamics of wandering albatross Diomedea exulans and Amsterdam albatross D. amsterdamensis in the Indian Ocean and their relationships with long-line fisheries: Conservation implications

Studies carried out over the past three decades at Crozet and Kerguelen Islands in the Indian Ocean indicate that wandering albatross Diomedea exulans populations declined markedly, but since 1986 have shown slow recovery. The population of the endangered Amsterdam albatross Diomedea amsterdamensis appears to have similarly recovered since 1985, but remains close to extinction. A demographic study of the Crozet population indicates that the earlier decline was mainly the result of increased adult mortality, and secondarily of low recruitment. Satellite tracking studies of breeding birds and band recoveries of non-breeding birds indicate that during and outside the breeding season these populations are in contact with long-line fisheries, mainly the pelagic Japanese southern blue-fin tuna Thunnus maccoyii fishery and to a lesser extent the Patagonian tooth-fish Dissostichus eleginoïdes fishery operating on the Kerguelen shelf. Decreased fishing effort and a concentration outside the central Indian Ocean by the Japanese fishery during recent years has probably resulted in the slow recovery of these albatross populations as a result of improved adult survival and recruitment. Long-line fisheries still represent a major threat to great albatross populations, most of which are still declining in the Southern Ocean. Possible conservation measures to reduce mortality in the fishery and to reduce contacts between fishing units and foraging albatrosses are examined.

Fatal encephalitis due to the scuticociliate Uronema nigricans in sea-caged, southern bluefin tuna Thunnus maccoyii

DAO Diseases of Aquatic Organisms Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials DAO 30:17-25 (1997) - doi:10.3354/dao030017 Fatal encephalitis due to the scuticociliate Uronema nigricans in sea-caged, southern bluefin tuna Thunnus maccoyii Munday BL, O'Donoghue PJ, Watts M, Rough K, Hawkesford T A syndrome characterized by atypical swimming behaviour followed by rapid death was first reported in captive southern bluefin tuna Thunnus maccoyii (Castelnau) in the winter of 1993. The cause of this behaviour was found to be a parasitic encephalitis due to the scuticociliate Uronemanigricans (Mueller). Based on parasitological and histological findings, it is proposed that the parasites initially colonise the olfactory rosettes and then ascend the olfactory nerves to eventually invade the brain. Possible epidemiological factors involved in the pathogenesis of the disease include water temperature (<18°C) and the immune status of the fish. Southern bluefin tuna · Thunnus maccoyii · Scuticociliate · Uronema nigricans ·Encephalitis · Neuritis Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in DAO Vol. 30, No. 1. Publication date: July 24, 1997 Print ISSN:0177-5103; Online ISSN:1616-1580 Copyright © 1997 Inter-Research.

Use of the bomb radiocarbon chronometer to determine age of southern bluefin tuna Thunnus maccoyii

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 143:1-8 (1996) - doi:10.3354/meps143001 Use of the bomb radiocarbon chronometer to determine age of southern bluefin tuna Thunnus maccoyii Kalish JM, Johnston JM, Gunn JS, Clear NP The growing otoliths of fish incorporate radiocarbon in concentrations that are equivalent to that found in ambient seawater dissolved inorganic carbon. Therefore, pulses of anthropogenic radiocarbon produced by the atmospheric detonation of nuclear weapons can ultimately be detected in otoliths. This study estimates the age of large southern bluefin tuna Thunnus maccoyii using an age estimation procedure based on the determination of levels of bomb-derived radiocarbon in their otoliths. Radiocarbon data from selected regions of southern bluefin tuna otoliths indicate that this species may reach ages in excess of 30 yr. Furthermore, individuals that approach the asymptotic length are likely to be 20 yr of age or older. The data agree generally with accepted models of southern bluefin growth, but show that these fish live longer than was believed previously. Comparisons between otolith section and bomb radiocarbon age estimates indicate that reading otolith sections is an effective method to estimate the age of larger southern bluefin. The presence of a significant number of individuals greater than 20 yr of age in the southern bluefin population may alter estimates of natural mortality rates currently used in Virtual Population Analysis models for stock assessment of this species. Age validation · Bomb radiocarbon chronometer · Carbon · Otoliths · Radiocarbon · Southern bluefin tuna · Thunnus maccoyii Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 143. Publication date: November 14, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Stock structure of the southern bluefin tuna Thunnus maccoyii: an investigation based on probe microanalysis of otolith composition

Analysis of the chemistry of calcified tissues has been suggested to be a source of useful information on the population structure and environmental history of fishes. We have investigated this approach as a means of determining the number of spawning areas and diversity of migration routes in the large pelagic scombrid, Thunnus maccoyii (southern bluefin tuna). Analysis was based on ontogenetic variation in the composition of sagittal otoliths, as measured using two probe microanalysers (wavelength dispersive electron probe microanalysis and proton-induced X-ray emission microanalysis), of 9 larvae collected on the single known spawning ground (NE Indian Ocean), of 29 juveniles caught at different points along the known migration routes (off western Australia, southern Australia, and South Africa), and of 14 adults caught in the high-seas fishery (off SE Australia). Fifteen elements were detected in T. maccoyii sagittae, but only six (Ca, Na, Sr, K, S, and Cl) were consistently present at concentrations above minimum detection limits. No attempt was made to measure the concentrations of C, N and O, which are assumed to also be present. Comparisons among different samples indicated that: (1) variation in the composition of the otolith primordium was unimodal and, generally, normally distributed; (2) this composition varied among specimens as a function of their size or, apparently, year-class; (3) individuals collected from widely separated locations did not differ clearly in the composition of the most recently deposited sections of their otoliths; and (4) all variation in the composition of adult otoliths was encompassed in the range of variation of juveniles collected along the major known migration route. These observations are consistent with the hypothesis of a single spawning area for T. maccoyii, but also indicate that the range of environmentally correlated variation in composition is too low to provide a robust test of the diversity of migration routes. It is not clear why this variation is so low, but we suspect that it reflects both the relative homogeneity of the pelagic environment and a weak effect of environmental factors on the concentration of elements present in otoliths at levels≳1 ppm.

Biochemical‐genetic identification of northern bluefin tunaThunnus thynnusin the New Zealand fishery

Abstract Muscle samples were collected from southern bluefin tuna Thunnus maccoyii off New Zealand, from northern bluefin tuna T. thynnus off Japan, and from specimens recorded as northern bluefin tuna off New Zealand. Electrophoretic analyses of muscle tissues from T. thynnus and T. maccoyii found 2 out of 33 enzyme loci with species‐specific gel phenotypes. These two markers were used to identify specimens recorded as “northern” bluefin tuna in the New Zealand fishery. Only two out of 17 “northern” specimens were T. thynnus.

Age, growth rate, and growth trajectory determined from otolith microstructure of southern bluefin tuna Thunnus maccoyii larvae

Age, growth rate, and growth trajectory determined from otolith microstructure of southern bluefin tuna Thunnus maccoyii larvae

An Experimental Determination of the Effect of Increasing the Minimum Age (or Size) of Fish at Capture upon the Yield per Recruit

The aim of this paper is to describe a tag release–recapture experiment designed to determine the quantitative effect of increasing the minimum age (or size) of fish at capture upon the yield per recruit for the current intensity of fishing, if the minimum age corresponding to the maximum catch weight per recruit for this fishing intensity is greater than the minimum age that currently applies in the fishery, this optimal minimum age can be determined from a single tag release–recapture experiment. The main advantage of the described tag release–recapture experiment over the experimental approach recommended in the past, but not yet applied, is a reduction in the use of trial and error procedures. Unlike the classical Beverton and Holt yield per recruit analysis, this approach does not require specific information on fish growth and natural and fishing mortalities. Consequently, it can be implemented for many complex fisheries systems. However, as with the classical approach, it does not enable useful predictions to be made when a change in the minimum age significantly alters the number of recruits to the fishable stock. The method of data analysis is developed and illustrated using data on southern bluefin tuna (Thunnus maccoyii).

The Effect of Parameter Uncertainties in an Age–Length Relationship upon Estimating the Age Composition of Catches

A simple, but frequently applied, procedure for decomposing fish length frequencies into age-classes is considered. This decomposition consists of converting fish lengths into ages using an age–length relationship. A method for assessing the effect of parameter uncertainties in this relationship upon estimates of the age composition of catches is presented. It is assumed that the parameter uncertainties can be described by probability distributions. Our aim is to determine probability distributions of age composition estimates resulting from these uncertainties. This is done using a stochastic sensitivity analysis technique involving Monte Carlo simulations and/or a first-order theory if such a theory is valid in the case under consideration. The method is illustrated by its application to data from the southern bluefin tuna (Thunnus maccoyii) fishery. It is found that simulated (Monte Carlo) catch estimates for age-classes 3 (fish at age 2–3 yr) to 13 (fish at age 12–13 yr) are normally distributed. The coefficients of variation of these estimates are less than 12%. Simulated catch estimates for age-classes 1, 2, and 14–20 deviate considerably from normality and their ranges bounded by the 2.5 and 97.5 percentiles are extremely wide; they include values different by up to 810% from the best deterministic catch estimates.Key words: catch, age composition, uncertainties, sensitivity analysis, Monte Carlo simulations, southern bluefin tuna