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.     

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.     

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。     

Gustatory responses in Pacific bluefin tuna Thunnus orientalis (Temminck and Schlegel)

Gustatory neural responses of the Pacific bluefin tuna Thunnus orientalis (Temminck and Schlegel) to extracted compounds of prey organisms, such as amino acids, nucleotide‐related substances, organic acids and organic bases, were electrophysiologically recorded from the facial nerve supplying the anterior palate. Of the 17 amino acids tested, l ‐proline was the most potent amino acid at 10^?2 M, and its threshold was the lowest at around 10^?6 M. l ‐leucine, l ‐methionine, l ‐alanine, l ‐valine and l ‐isoleucine were also highly stimulatory at 10^?2 M; however, the other 11 amino acids examined were not as effective or were ineffective. Thus, the gustatory receptors for amino acids of the Pacific bluefin tuna show a narrowly tuned response profile. Among the seven nucleotide‐related substances tested, uridine‐5′‐monophosphate, inosine‐5′‐monophosphate and adenosine‐5′‐diphosphate were highly stimulatory, and their thresholds were 10^?4–10^?5 M. Inosine elicited a positive response at 10^?2 M but its response magnitude was not so high. Organic acids l ‐lactic and pyruvic acids were effective at 10^?2 M, but no response was elicited at 10^?3 M. Among organic bases, betaine was highly stimulatory, and its response magnitude at 10^?2 M is almost equal to that of l ‐proline at the same concentration. The threshold for betaine was determined to be at around 10^?5 M. Trimethylamine oxide and ammonium chloride were ineffective.     

漂流人工集鱼装置随附鱼群中鲯鳅的生物学特征

漂流人工集鱼装置(fish aggregation devices,FAD)在金枪鱼围网渔业中被广泛地应用于诱集捕捞金枪鱼类。鲯鳅作为漂流FAD诱集鱼群中最为常见的兼捕种类之一,研究其生物学特性有助于了解其种群结构,对于合理保护该资源具有重要意义。利用2010-2013年间中西太平洋金枪鱼围网渔业科学观察员在5°N~10°S,145°E~170°E海域内收集的189尾鲯鳅样本,对其叉长分布、性比、性成熟度及摄食等生物学特性进行研究。结果表明:鲯鳅叉长范围为10.0~126.3 cm,优势叉长为70.0~100.0 cm,占总数的66.7%;雌雄性别比为4.1∶1;样本以性成熟(Ⅴ~Ⅵ期)个体为主,占总数的73.6%,50%性成熟叉长(L50)为49.95 cm;76.0%的样本为空胃,而实胃中频现其它常见的小型随附鱼种,如鲣(Katsuwonus pelamis)的幼鱼、细鳞圆鲹(Decapterus macarellus)、六带鲹(Caranx sexfasciatus)、疣鳞鲀(Canthidermis maculata)和单角革鲀(Aluterus monoceros)。渔业生物学信息表明漂流FAD下的鲯鳅群体以性成熟的大型个体为主,FAD对于雌鱼具有更强的聚集效果,觅食是鲯鳅游向漂流物的可能动机之一。     

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.     

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.

     

Completion of the Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel) life cycle

Tuna aquaculture is currently dependent on the wild capture of juveniles for production. The development of hatchery technology for bluefin and other tunas would be a major step forward in improving sustainability of their aquaculture. The present study overviews the technology in the life cycle completion of the Pacific bluefin tuna (PBT) Thunnus orientalis (Temminck et Schlegel) under aquaculture conditions in Kinki University, and the problems to be solved for the establishment of tuna hatchery technology. On 23 June 2002, broodstock of PBT that were artificially hatched and reared spontaneously spawned in captivity. The resulting eggs hatched and were subsequently reared to the juvenile stage. The spawning fish were the result of a research project started in 1987 to rear wild‐caught juvenile PBT that were several months old. Fertilized eggs were obtained from these fish in 1995 and 1996. Resulting juveniles (the artificially hatched first generation) were reared to maturity and spawned in 2002. Over the summer of 2002, 1.63 million eggs from these fish were used for a mass rearing experiment, and 17 307 juveniles were produced and transferred to an open sea net cage. Of these artificially hatched second‐generation PBT, 1100 grew to approximately 95 cm total length and 14 kg body weight in 22 months. This procedure means the completion of PBT life cycle under aquaculture conditions, which was first attained among large tuna species. The problems awaiting solution in PBT hatchery production are their unpredictable spawning in captivity, to improve survival during the first 10 days post hatch, to reduce cannibalism in larval and juvenile stages, and to solve collision problem causing high mortality during the juvenile stage.     

Why do young Pacific bluefin tuna repeatedly dive to depths through the thermocline?

Young Pacific bluefin tuna Thunnus orientalis with archival tags were released in the East China Sea. Time-series data for depth, and ambient and peritoneal temperatures for nine fish, recorded every 128 s, were analyzed. Our objectives were to describe monthly changes in diving patterns in relation to the ambient thermal structure and the occurrence of feeding events during March–June, and to discuss possible reasons why bluefin tuna repeatedly dived to depths below the thermocline in terms of their thermoconservation mechanisms. It was found that the fish repeatedly dived through the thermocline at intervals of 1.2 h on average, and the dive frequency was high during March–May. However, the dive frequency and periodicity decreased in June, when the gradient became steeper. In contrast, feeding events increased in June. These results indicate that from March to May, bluefin tuna repeatedly dive because food biomass is inadequate at the surface, and they stop undertaking repeated dives in June when food becomes more readily available at the surface, in addition to low visibility caused by low solar radiation. Further, the range of heat transfer times for these fish was so long that their peritoneal temperature was probably maintained by engaging in brief dives. The periodicity of dives may lead to a lower fluctuation in the peritoneal temperature, suggesting that the dives are a kind of behavioral thermoregulation.