9 research outputs found

    Preliminary age-based life history characteristics of the dogtooth tuna, Gymnosarda unicolor (Ruppell, 1838), in the southwest Pacific Ocean

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    Dogtooth tuna, Gymnosarda unicolor were sampled off the east coast of Australia (southwest Pacific Ocean) from 2007 to 2012. Ages were determined by examining thin transverse sections of their sagittal otoliths and were based on counts of alternating opaque and translucent zones (annual growth increments). Growth was rapid during the first year of life, after which growth in length was much reduced. Parameters of the constrained von Bertalanffy growth function (fork length-at-age) were L∞ = 1164.77 (mm, FL) and K = 0.44 year−1. Preliminary estimates of longevity indicate a maximum observed age of at least 20 years. There was a high degree of variation in the observed length and age of sexual maturity for G. unicolor. Despite this variation, the size at 50% maturity for female G. unicolor estimated in this study was 713 mm FL (<2 years of age). The diet of G. unicolor is very broad and covers a range of fish species. The life history characteristics of G. unicolor overall, indicate that this species may be somewhat resilient to fishing. However, reports of localised depletions, in association with heavy targeting by sports fishers, low effective population sizes and patchy recruitment indicate that this species is particularly vulnerable to overfishing

    Determination of annual periodicity in annuli formation in Atlantic bluefin tuna otoliths.

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    Controversies remain regarding the periodicity, or seasonality, of otolith growth band formation which directly influences a correct age determination of Atlantic bluefin tuna using otoliths. Thereby, the aim of this work was to apply marginal increment analysis (MIA) and marginal edge analysis (EA) to determine the timing of band deposition. The index of completion (MIA) was also analyzed using General Additive Models. Results indicated that the opaque band begin to form in July and would finish forming in November. From the end of the year and the beginning of the following year there is minimal marginal edge growth and this is when the translucent band begins to form and reaches its maximum development in June. MIA and EA has evidenced that the annulus has been formed in November in the Atlantic Bluefin tuna otolith. This would mean to delay the date of the current July 1st adjustment criterion to November 30

    REPORT OF THE ICCAT GBYP INTERNATIONAL WORKSHOP ON ATLANTIC BLUEFIN TUNA GROWTH

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    In the last Atlantic bluefin tuna assessment, an age-length database coming from direct ageing was presented for the first time. It was observed that otolith age estimates for fish younger than 8 years old had a smaller size at age compared to spine (first dorsal fin radius) age estimates. This difference, although small, was enough to misallocate the year class. This misallocation was solved when introducing a vector of bias corrected aged otoliths based on paired otolithspine samples. We have identified two possible causes for over-estimating age in the otolith agelength data: the current age adjustment criterion (to convert the bands counting into ages) and a reading bias in age estimations from some laboratories. Otolith preparation and reading protocols have been reviewed. The edge type and marginal increment analysis showed that the formation of opaque zones would seem likely to occur primarily between December through to June, contrary to what was thought until now, for which a new criterion for age adjustment has been proposed

    Report of the ICCAT GBYP international workshop on Atlantic bluefin tuna growth

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    In the last Atlantic bluefin tuna assessment, an age-length database coming from direct ageing was presented for the first time. It was observed that otolith age estimates for fish younger than 8 years old had a smaller size at age compared to spine (first dorsal fin radius) age estimates. This difference, although small, was enough to misallocate the year class. This misallocation was solved when introducing a vector of bias corrected aged otoliths based on paired otolithspine samples. We have identified two possible causes for over-estimating age in the otolith agelength data: the current age adjustment criterion (to convert the bands counting into ages) and a reading bias in age estimations from some laboratories. Otolith preparation and reading protocols have been reviewed. The edge type and marginal increment analysis showed that the formation of opaque zones would seem likely to occur primarily between December through to June, contrary to what was thought until now, for which a new criterion for age adjustment has been proposed

    Indicators of recovery for orange roughy (Hoplostethus atlanticus) in eastern Australian waters fished from 1987

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    © 2015 .Compared to an 18 year New Zealand study (. Clark et al., 2000) we found multiple signs of recovery for orange roughy in Australian waters. Orange roughy were listed as conservation dependent in Australian waters in 2006, with most stocks reported to be well below 20% of estimated pre-fishing equilibrium biomass and closed to targeted fishing. The largest known spawning aggregations occur on the east coast of Tasmania. This area has been fished and monitored since 1987. A specific monitoring programme was established in 2006 to determine whether and at what rate the spawning sites would rebuild. Acoustic biomass estimates were on average 1.5 times higher than that expected from a recent stock assessment and between 2006 and 2013 have shown an increasing then decreasing trend. Positive signs of a population recovery include an increased biomass at the spawning sites since fishing ceased, large change in the age structure of the population and a 74% increase in the reproductive potential of females since 1987. Given the late maturation of orange roughy entering the spawning biomass (~30 years) and the short duration of fishing (~26 years), these changes represent pre-fishing recruitment still entering the fishery. Biomass, age and length frequency data were variable between and within spawning sites; this complicates the use of a single or multiple spawning sites to monitor the exploitation and recovery of the fishery

    Lead-radium dating provides a framework for coordinating age estimation of Patagonian toothfish (Dissostichus eleginoides) between fishing areas

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    Patagonian toothfish (Dissostichus eleginoides) or ‘Chilean sea bass’ support a valuable and controversial fishery, yet their life history is not well understood and longevity estimates range from ~20 to >50 years. In this study, lead–radium dating provided valid ages for juvenile to older adult groups, which were consistent with the counting of otolith growth zones in transverse otolith sections, and longevity estimates exceeding 30 years. Lead–radium dating revealed minor biases between the radiometric age and interpretation of growth zone counting for regional fishing areas monitored by two facilities, Center for Quantitative Fisheries Ecology (CQFE) and the Central Ageing Facility (CAF), using different age estimation techniques. For CQFE, under-ageing of ~3.3 years was observed for individuals with estimated ages under 20 years. For the CAF, ages were overestimated for young fish and underestimated for the oldest fish. Lead–radium dating detected underlying problems in coordinating age estimation between geographically separated fish stocks, and provided a framework to objectively assess otolith interpretation and growth modelling between laboratories based on age-validated data

    Thiyl Radicals in Organic Synthesis

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