中国金枪鱼围网船队大眼金枪鱼渔获物的特征变化与人工集鱼装置禁渔期的关系

研究了2012-2015年中国金枪鱼围网船队大眼金枪鱼(Thunnus obesus)渔获物的特征变化与人工集鱼装置(fish aggregation devices,FAD)禁渔期的关系,文章收集了2012-2015年中国大陆金枪鱼围网船队在中西太平洋的渔捞日志数据,对随附鱼群捕捞努力量与小体大眼金枪鱼和大体大眼金枪鱼的船均产量进行分析比较。结果显示:1)从2013年开始,对随附鱼群投网的次数占总投网次数的比例有所降低,均不超过50%;2)K-S检验显示研究期内禁渔期前后的船均随附鱼群网次存在显著差异(P0.05);3)2013-2015年大眼金枪鱼渔获量的平均水平明显低于2012年;4)从2013年开始,禁渔期结束后的第一个月(即11月)的船均产量都发生猛增;5)从捕捞努力量与渔获量的相关性结果看,不论是小体大眼金枪鱼还是全部大眼金枪鱼,2013年和2014年两者都呈现出显著的强正相关关系(P0.05)。这些结果表明2012年以后中国船队对大眼金枪鱼幼鱼的兼捕水平有所下降,延长FAD禁渔期的管理措施对于保护大眼金枪鱼幼鱼在某些年份可能具有一定的效果。     

Spawning induction and seed production of Eastern little tuna,Euthynnus affinis (Cantor, 1849), in the post‐ and pre‐spawning seasons by hormonal treatment in a semi‐closed recirculation system with elevated temperature

We previously established a method for spawning induction in Eastern little tuna (ELT) Euthynnus affinis (Cantor, 1849) by administering a gonadotropin‐releasing hormone analog (GnRHa) during the natural spawning season in Japan (August–October). In order to establish seed production of ELT in the off‐spawning season, we first conducted three spawning induction trials by GnRHa administration from October 2011 to January 2012 using ELT broodstock (2 years old; three females and four males) maintained in a 10‐m³ tank with a semi‐closed recirculation system and static elevated temperature. Average water temperature and daily egg production in three trials lasting 11–15 days were 27.0 ± 0.09°C and 268 173 eggs (Trial 1), 27.0 ± 0.11°C and 277 9098 eggs (Trial 2), and 25.5 ± 0.39°C and 291 113 eggs (Trial 3) respectively. Mean fertilization rate and mean hatching rate were 70.4% and 60.5% (Trial 1), 83.9% and 79.6% (Trial 2), and 62.5% and 57.4% (Trial 3) respectively. We also succeeded in producing ELT larvae in the pre‐spawning season (April–July), although the quantity and quality of larvae produced were inferior to those produced in other calendar months. In trials involving periodic GnRHa administration during the off‐spawning seasons, hatched larvae were obtained in the 10‐m³ tank after six of nine administrations in the 2011–2012 off‐spawning season and in 16 of 19 administrations in the 2012–2013 off‐spawning season. The findings of this study demonstrated that hormonal treatment and thermal control could be used to extend the spawning period in ELT, potentially allowing larval production in the post‐ and pre‐spawning seasons.     

Shooting fish in a barrel? Assessing fisher‐driven changes in catchability within tropical tuna purse seine fleets

With constant innovation to find more efficient ways to find, catch and process fish, catchability in wild fisheries can increase. Catchability is a combination of resource abundance, fishing effort and fishing efficiency: any increase in fleet efficiency can lead to undesirable effects not only on stocks, but also on the ability to assess them. When using effort controls as part of management, it is necessary to adjust for the increase in catchability due to the increases in efficiency over time to avoid stock depletion. Accounting for changes in catchability can be problematic for pelagic stocks, due to the changes in fishing behaviour and the continual change in fishing efficiency. This study investigates the success in finding patches of fish for fleets operating within the western and central Pacific purse seine fishery between 1993 and 2012. Three indices, widely used in ecological research, were used to study how spatial variation in fisher behaviour for sets on fish aggregating devices (FADs) and free‐school sets was related to catchability. For free‐school set types, the diversity index was negatively correlated with Katsuwonus pelamis catchability. When this index was low, catch rates were at their highest and there was a reduction in the area fished. In contrast, for FAD sets, catches increase when the patchiness index was low, implying a degree of random behaviour, potentially due to advances in FAD technology. An improved understanding of the spatial allocation of effort can improve catchability estimates widely used for fisheries stock assessments and in indices of global biodiversity.     

热带大西洋与热带太平洋拟锥齿鲨生物学特征比较

拟锥齿鲨(Pseudocarcharias kamoharai)是金枪鱼延绳钓渔业中较常见的兼捕物种。它处于海洋生态结构的顶端,对海洋生态系统的稳定和多样性起着非常重要的作用。根据我国金枪鱼渔业国家观察员2011~2015年在热带大西洋海域(6.38°S~15.17°N、42.02°W~18.53°W)调查时采集的1 426 ind拟锥齿鲨和2006~2015年在热带太平洋海域(16.88°S~10.85°N、148.71°E~96.80°W)调查时采集的1 037 ind拟锥齿鲨,按不同性别对其生物学特征进行初步研究和比较。结果表明:热带太平洋、热带大西洋两海域拟锥齿鲨雄性和雌性之间在平均叉长、优势叉长方面均存在显著性差异(P0.05),热带太平洋海域的拟锥齿鲨优势叉长和平均叉长值更大;两洋区雄性和雌性拟锥齿鲨叉长与全重关系均存在显著性差异(P0.05);两洋区拟锥齿鲨的雌雄性比分别为1∶0.80和1∶1.71,具显著性差异(P0.05);在拟锥齿鲨的摄食等级、肝重指数和繁殖特征上两洋区无显著性差异(P0.05)。     

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。     

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。     

Mass spectrometric detection of proopiomelanocortin (POMC)-related peptides following molecular cloning of POMC cDNA in bigeye tuna Thunnus obesus

Several pituitary hormones, including adrenocorticotropin (ACTH), melanotropin (MSH) and β-endorphin, are generated from a common precursor protein, proopiomelanocortin (POMC). In fish, in addition to steroidogenesis of ACTH and melanogenesis of MSH, immunomodulating activity has been found in some POMC-related peptides. To investigate the functions of these peptides in the homologous system, it is necessary to establish a convenient detection method for the peptides. The present study aimed to establish a method for the detection of POMC-related peptides in bigeye tuna Thunnus obesus using a small amount of tissue sample, but not requiring peptide purification. We first determined the nucleotide sequence of tuna POMC cDNA. The cDNA was composed of 1084 base pairs (excluding the poly A tail) that encoded POMC consisting of 222 amino acids. We then fractionated an acid-acetone extract of one pituitary by reverse-phase high performance liquid chromatography (HPLC) and determined the molecular weight of each separated peptide by mass spectrometry. Consequently, we detected eight POMC-related peptides by comparing the values to the deduced amino acid sequence. Thus, the present study enabled the detection of POMC-related peptides from a small amount of tissue without the use of several purification steps.