Changes in frigate tuna populations on the south coast of Sri Lanka: evidence of the shifting baseline syndrome from analysis of fisher observations

• 1. This study examines changes in frigate tuna populations in southern Sri Lanka, based on reports from fishers in three age classes. Significantly higher values for best day's catch and largest specimen ever caught were obtained by older fishers than younger ones. Values were also significantly higher during early years, providing clear evidence of a decrease in the resource over time (1951–2007).
• 2. Older fishers reported best catches further inshore and in shallower waters which, on becoming depleted, forced younger generations to fish in less exploited areas further offshore. Heavy harvesting is also evident from the significantly greater number of sites reported by older fishers as being depleted, compared with observations of younger fishers.
• 3. These findings contrast markedly with catch and catch per effort patterns from statistics for frigate tuna and bullet tuna (combined) in southern Sri Lanka (1994–2004). No stock decline is evident, and at least one report in the early 1990s advocated increasing exploitation rates by 40% to maximize yields.
• 4. Although not a primary research objective, fisher observations on frigate tuna populations were also analysed to help evaluate possible effects of the 2004 tsunami. Most fishers reported post‐tsunami decline, but mainly from a larger new generation of fishers, rather than extra boats provided by aid money or (direct or indirect) biophysical impacts from the tsunami.
• 5. Reliance on fishery statistics, especially for mixed species and over a limited period, can be risky and easily mask true stock status. Evidence of harvesting effects on frigate tuna in southern Sri Lanka is evident using questionnaire data over a longer time scale.
• 6. This study provides another compelling case of the ‘shifting baseline syndrome’, whereby fishers of different ages have altered perceptions/experiences of their environment. This may be its first reported occurrence in Sri Lanka. Traditional knowledge from this and similar surveys may provide national fishery management with valuable insights and help improve conservation prospects for frigate tuna and other marine resources. Copyright © 2009 John Wiley & Sons, Ltd.

     

印度洋大眼金枪鱼延绳钓适宜渔获环境的初步研究

数值分析得出大眼金枪鱼的渔获适宜环境参数值范围：温度14～17℃，盐度34．5～35．4．溶解氧浓度1．5～4．5mg／L，温跃层深度80～160m，营养盐氮、磷、硅浓度分别大于12-μg／L，09μg／L，14μg／L。聚类分析表明，钓获率与营养盐关系最为密切。另外，通过因子分析，深化了对钓获率和渔获环境因子两者间关系的理解。     

Changes of proximate compositions and myoglobin content in the dorsal ordinary muscles of the cultured Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis> with growth

ABSTRACT:   Using the dorsal ordinary muscle (DOM) of cultured Pacific bluefin tuna (body length [BL]: 47.5–81.8 cm, body weight [BW]: 2.1–13.5 kg, n  = 15), the changes of proximate compositions and myoglobin (Mb) content with growth were investigated. There was a positive correlation ( r  = 0.9832, P  < 0.05) of BL and BW in cultured tuna. The protein contents of the DOM of cultured tuna decreased ( P  < 0.05) and the lipid contents had a tendency to increase (not significantly) with growth. The meat color changed from pink to red with growth. In addition, the Mb contents of the DOM of cultured tuna increased ( P  < 0.05) from 1.0 mg/g (minimum BW fish) to 3.8 mg/g (maximum BW fish) with growth. These results indicate that the increase of the Mb content in the DOM of cultured tuna is not caused by the restriction of exercise and overfeeding between 2.1 kg and 13.5 kg of BW.     

Dynamic simulation of tuna longline gear using numerical methods

ABSTRACT:   The underwater shape and hook depth of tuna longline gear are important factors determining fishing performance. In this study, how the shape of tuna longline gear changes in response to sea conditions and gear rigging is explained. Physical models of underwater gear shape were made to simulate fishing gear and analyzed according to the direction and velocity of currents. Then experiments with small-scale models were conducted in a flume tank to confirm the accuracy of the simulation analysis. Finally, the simulation was examined relative to actual longline fishing gear. This approach provided an improvement over previous analytical methods that did not consider fishing gear shape in response to different sea conditions. A useful result is an improved understanding of the relationship between ocean currents and the configuration of longline gear (the shortening ratio, and number of hooks per basket). These factors affect hook depth which, in turn, affects selectivity. Application of these results could lead to more effective and efficient fishing under different sea conditions.     

Spatial differentiation in the eastern Pacific yellowfin tuna revealed by microsatellite variation

ABSTRACT:   Five eastern Pacific yellowfin tuna samples (four northern: 10–25°N, 95–130°W, and one southern: 16–18°S, 95–97°W), collected from fishing vessels between 1994 and 2002 were analyzed for variation at seven microsatellite loci to evaluate their spatial genetic homogeneity. Single-locus homogeneity exact tests revealed significant genetic differentiation caused by three of seven loci. Pairwise sample comparisons of multilocus allele-frequency homogeneity tests and subpopulation division ( F _ST), revealed significant differentiation in comparisons between north equatorial samples and the south equatorial sample. amova analysis among collections grouped as northern and southern populations separated by the equator in the eastern Pacific confirmed the differentiation observed. These results may be considered as preliminary evidence of the presence of discrete populations in the eastern Pacific yellowfin tuna. The possibility that the spatial differentiation observed corresponds to temporal variation or non-random sampling cannot be discarded. The genetic differences encountered need to be corroborated by increasing sample sizes, including temporal replicates, and by the use of an alternative marker.     

金枪鱼延绳钓捕捞作业状态的数值模拟

一种基于有限元原理的非线性混合法被用于预测捕捞作业中的金枪鱼延绳钓的形状与张力，为渔具设计提供理论方法，并以期在设计阶段能替代传统的水槽模型试验，为实际渔业生产作业调整提供有益的技术参数。构成延绳钓渔具的绳索可以被一系列绝对柔软的被称为绳索要素的单元所模拟，因此，整个延绳钓渔具可以被看作为一系列绳索要素在其两端点通过无摩擦铰接连接而成的集合体。根据最小位能原理，可以导出描述系统平衡状态的非线性基本平衡方程式。利用Newton-Raphson方法，通过一系列的负荷-形状迭代法求解基本平衡方程式，可以获得海流作用下延绳钓渔具作业时的形状和张力分布的数值解。简化模型的回流水槽试验验证表明，本方法具有较好的计算精度和解的收束性与稳定性。     

Total mercury and methylmercury levels in commercially important fishes in Japan

ABSTRACT:   The distribution of mercury in the muscle and other tissues was determined in 23 species of fishes and invertebrates. This study reveals species-specific patterns of mercury accumulation in the muscle of tuna and alfonsino. Consistently high levels of total mercury were found in Beryx splendens (0.78 ± 0.56 µg/g), Atlantic Thunnus thynnus (0.42 ± 0.06 µg/g), Pacific T. thynnus (0.59 ± 0.34 µg/g), Thunnus obesus (0.98 ± 0.34 µg/g), Makaira nigricans (0.56 ± 0.05 µg/g), Tetraptrus audax (0.51 ± 0.08 µg/g), and Xiphias gladius (0.47 ± 0.24 µg/g). Other fish species had lower levels of total mercury or methylmercury in muscle than the maximum permitted level of mercury in fish in Japan (0.4 µg/g). Total mercury and methylmercury levels in the muscles of T. thynnus , T. obesus, and B. splendens were closely correlated with body weight.     

Structural and thermodynamic characterization of tropomyosin from fast skeletal muscle of bluefin tuna

ABSTRACT:   Tuna tropomyosin is a mixture of nearly equimolar amounts of two isoforms (designated α and β). cDNA encoding the α form was cloned from bluefin tuna Thunnus thynnus fast skeletal muscle. The full-length cDNA contained 1220 bp, comprising an open reading frame of 855 bp encoding 284 amino acid residues, flanked by 5'-untranslational regions (156 bp) and 3'-untranslational regions (209 bp). The deduced amino acid sequence showed considerably high homology in a range of 93.7–98.6% to those of other vertebrate α-type tropomyosins. In phylogenetic analysis, bluefin tuna tropomyosin showed the closest relationship with the white croaker counterpart. The predicted mass was 32 919 Da, and isoelectric point was 4.50, assuming acetylation of the N-terminus. By differential scanning calorimetry, bluefin tuna tropomyosin gave two major endothermic peaks at 29.3 and 41.5°C, probably caused by the presence of two isoforms. Circular dichroism spectra supported such a unique denaturation profile.     

中西太平洋金枪鱼围网黄鳍金枪鱼渔获时空分析

中西太平洋的金枪鱼围网渔业目前的年产量约在1×106t左右,其中黄鳍金枪鱼占有很重要的地位。本文通过对围网捕获的黄鳍金枪鱼渔获数据进行时间序列以及空间位置变化等时空分析,试图找出其变化规律以及趋势。结果表明,20世纪70年代以来,随着渔船数的增加,中西太平洋围网捕获的黄鳍金枪鱼渔获量分布,从太平洋岛屿近海逐渐向太平洋热带中部海域扩展。渔获量经度重心随着中西太平洋金枪鱼围网渔业的发展有向东移动的趋势,70年代在128°E附近,到80年代在145°E左右,90年代在152°E左右,近年在155°E左右。而黄鳍金枪鱼渔获量纬度重心位于赤道区域,70年代在3°30′N附近,80年代在0°30′N左右,90年代在0°40′S左右,近年在1°20′S左右。经纬度5°×5°小区范围内10年内的最高总产量则从70年代的8×104t,增加到90年代超过20×104t。渔获量空间分布除了随着渔业发展向外海扩展以外,还受到被称为南方涛动的ENSO现象的明显影响,一般来说渔获量经度中心在厄尔尼诺年比较偏东,在拉尼娜年比较偏西,渔获量纬度重心在厄尔尼诺年或次年比较偏南,在拉尼娜次年比较偏北。此外,黄鳍金枪鱼渔获量经度重心在厄尔尼诺年变化比较大,渔获量纬度重心在厄尔尼诺年或次年变化比较大。