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51.
Feeding habits of albacore Thunnus alalunga in the transition region of the central North Pacific 总被引:2,自引:0,他引:2
Hikaru WATANABE Tsunemi KUBODERA Suguru MASUDA Shigeyuki KAWAHARA 《Fisheries Science》2004,70(4):573-579
ABSTRACT: The feeding habits of albacore Thunnus alalunga (fork length: 48.9–76.2 cm, n = 132) were examined from late spring to early autumn in relation to its northward migration in the transition region between the subtropical and subarctic fronts in the central North Pacific. Samples were collected at night using surface gill nets or during daytime pole-and-line surveys in 2001 and 2002. During May and June, albacore fed mainly on Japanese anchovy Engraulis japonicus , which accounted for 27.2%, 67.0%, and 45.5% of the total stomach contents by number ( Cn ), wet weight ( WW ), and frequency of occurrence ( F ), respectively, and secondarily on the subarctic gonatid squid Gonatopsis borealis ( Cn , 15.8%; WW , 10.8%; F , 28.8%). From July to September, albacore continued to depend on Japanese anchovy ( Cn , 48.2–52.8%; WW , 79.9–95.2%; F , 27.8–85.4%). These results corresponded well with the remarkable rebound of the Japanese anchovy stock since the 1990s. Gonatopsis borealis , the main squid prey from May to June, almost disappeared from the stomachs of albacore from July to September, probably due to the northward migration of this squid to subarctic waters in summer. The feeding impact of albacore on the Japanese anchovy stock in the transition region was conservatively estimated to be from 1400 to 2100 tons per day from late spring to early autumn. 相似文献
52.
淡水养殖梭鱼的人工繁殖机理 总被引:1,自引:1,他引:1
1982~1986年;作者采用外源药理学方法,使淡水养殖梭鱼(S‰0.297-0.569)克服了“淡水不育症”,雌鱼性腺成熟率85%以上,完全取代了“海水过渡”。在人工催产中又克服了排卵机制的障碍及胚胎对环境的不适应,并对梭鱼亲鱼血清激素含量进行放射免疫(RIA)测定及电子显微镜对梭鱼脑垂体亚显微结构进行观察。提出梭鱼存在血脑屏障。 相似文献
53.
通过水稻干燥和缓苏过程中稻谷爆腰产生的玻璃化转变分析,确定稻谷在玻璃态下干燥时对爆腰增殖无影响。建议采用2种措施:一是使稻谷在玻璃态下干燥,抑制爆腰产生;二是使稻谷在较高温度下干燥一定时间后,给稻谷缓苏足够时间以降低内部水分梯度,使内部水分均匀,有效地降低稻谷裂纹率和提高产米率。 相似文献
54.
目的:探讨广东省大学生生活方式现状,分析其特点及社会学原因。方法:采用自制的大学生生活方式问卷,调查了广东省12所高校2136名大学生。结果:广东省大学生生活方式总均分为3.55±0.42。生活方式7个维度中,得分居前的是生命欣赏和饮食营养两个维度,居后的是运动锻炼和性健康两个维度。结论:(1)广东省大学生活方式总体处于中等水平;(2)性别、是否独生子女对大学生生活方式总得分均无显著影响,但在具体维度上存在影响;(3)从大一到大三,大学生生活方式呈下降趋势,但大四时有所回升;(4)家庭收入、居住地、父母文化程度对子女生活方式存在有限影响。 相似文献
55.
无线射频识别技术(RFID)的实施,使图书馆实现了智能化和自动化管理,在此新的管理模式下,图书馆的馆员角色需要重新定位。本文介绍了RFID自助借还系统的优势,分析、探讨了新技术环境下图书馆馆员角色的转换。 相似文献
56.
庞娟 《金陵科技学院学报》2014,(1):41-46
应用分子动力学方法模拟了聚合度为100的聚N-异丙基丙烯酰胺分子链在真空和稀水溶液中的构象转变。可以观察到分子链在500K下逐渐发生蜷缩,末端距下降,与实验现象定性一致。此外,研究结果还表明,随着温度的升高,高分子链重复结构单元NiPA上(C)O和(N)H基团均发生明显的去溶剂化作用,且高分子链段间发生聚集。 相似文献
57.
Coexistence of anadromous and lacustrine life histories of the shirauo, Salangichthys microdon 总被引:1,自引:0,他引:1
The environmental history of the shirauo, Salangichthys microdon, was examined in terms of strontium (Sr) and calcium (Ca) uptake in the otolith, by means of wavelength dispersive X‐ray spectrometry on an electron microprobe. Anadromous and lacustrine type of the shirauo were found to occur sympatric. Otolith Sr concentration or Sr : Ca ratios of anadromous shirauo fluctuated strongly along the life‐history transect in accordance with the migration (habitat) pattern from sea to freshwater. In contrast, the Sr concentration or the Sr : Ca ratios of lacustrine shirauo remained at consistently low levels throughout the otolith. The higher ratios in anadromous shirauo, in the otolith region from the core to 90–230 μm, corresponded to the initial sea‐going period, probably reflecting the ambient salinity or the seawater–freshwater gradient in Sr concentration. The findings clearly indicated that otolith Sr : Ca ratios reflected individual life histories, enabling these anadromous shirauo to be distinguished from lacustrine shirauo. 相似文献
58.
Takashi Kitagawa Shingo Kimura Hideaki Nakata Harumi Yamada 《Fisheries Oceanography》2004,13(3):161-180
Twenty‐four archival tags were recovered from Pacific bluefin tuna previously released off Tsushima Island in the East China Sea. By analysis of the time‐series data of the pressure and the ambient and internal temperature from the 24 tags, we examined the relationship between the tuna's pattern of diving and the thermocline depth. In the East China Sea, diving and feeding events occurred throughout almost the entire day in both winter and summer, suggesting that the purpose of diving is for feeding. In summer, the feeding frequency was greater than that in winter, which corresponds to the fact that growth is more rapid in summer than in winter. During summer in the Kuroshio–Oyashio transition region, on the other hand, feeding events were much more frequent than those in the East China Sea, in spite of a lower diving frequency. The mean horizontal distance traveled was also significantly higher and it seems that in this area they may move horizontally to feed on prey accumulated at the surface. We conclude that, in addition to the ambient temperature structure, the vertical and horizontal distribution of prey species plays an important role in the feeding behavior of Pacific bluefin tuna. One bluefin tuna migrated to the Oyashio frontal area, where both the horizontal and the vertical thermal gradients are much steeper. The fish spent most of the time on the warmer side of the front and often traveled horizontally to the colder side during the day, perhaps to feed. This implies that there is a thermal barrier effect, in this case from the Oyashio front, on their behavior. The frequency of feeding events was low, although all the monitored fish dived every dawn and dusk, irrespective of the seasons or location. It is possible that these twice‐daily diving patterns occurred in response to the change in ambient light at sunrise and sunset. 相似文献
59.
以二级相变铁电材料为例,利用推广的Ginzburg-Landau-Devonshire(GLD)理论,研究不均匀结构对梯度铁电薄膜性质的影响.结果表明:退极化场对于两层薄膜中间的极化影响较小,而在薄膜的两端处影响最大;梯度铁电薄膜的平均极化随膜厚按线性规律变化;在接近相变温度时,自发极化消失,梯度铁电薄膜的这一现象与铁电材料的性质相同.在外场不等于零的情况下,得到的梯度铁电薄膜的电滞回线中心对称. 相似文献
60.