Travelling light: white sharks (Carcharodon carcharias) rely on body lipid stores to power ocean-basin scale migration

Many species undertake long-distance annual migrations between foraging and reproductive areas. Such migrants depend on the efficient packaging, storage and utilization of energy to succeed. A diverse assemblage of organisms accomplishes this through the use of lipid reserves; yet, it remains unclear whether the migrations of elasmobranchs, which include the largest gill breathers on Earth, depend on such a mechanism. We examine depth records from pop-up satellite archival tags to discern changes in buoyancy as a proxy for energy storage in Eastern Pacific white sharks, and assess whether lipid depletion fuels long-distance (approx. 4000 km) migrations. We develop new algorithms to assess body condition, buoyancy and drift rate during drift dives and validate the techniques using a captive white shark. In the wild, we document a consistent increase in drift rate over the course of all migrations, indicating a decrease in buoyancy caused by the depletion of lipid reserves. These results comprise, to our knowledge, the first assessment of energy storage and budgeting in migrating sharks. The methods provide a basis for further insights into using electronic tags to reveal the energetic strategies of a wide range of elasmobranchs.     

Young whale sharks, Rhincodon typus, feeding on a copepod bloom near La Paz, Mexico

Seven small (3.2 to 5.2 m total length) whale sharks were observed suction feeding on patches of surface plankton in the Bay of La Paz within 1 km of shore and 2 km N of the phosphate dock at San Juan de la Costa, on 1–2 November 1993. The sharks were photographed and videotaped from the boat and by snorkelers in the water. When actively feeding the shark turned its head from side to side, part of the head was lifted out of the water, and the mouth opened and closed 7 to 28 times per minute (x=17, N=13). These suction gulps were synchronized with the opening and closing of the gill slits. This feeding behavior occurred only in the patchy areas of densely cloudy water, a layer 10 to 30 cm thick at the surface containing an immense concentration of copepods, 95% of which were identified as Acartia clausi. Remoras accompanying the whale sharks also fed on the plankton bloom. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vertical, lateral and longitudinal movement of zooplankton in a large river

1. The spatial distribution and movement patterns of zooplankton in large rivers are little known compared with those in lake environments. We conducted a series of studies in the Ohio River (U.S.A.) during the low flow period to assess diel vertical (DVM), longitudinal and lateral movement of crustacean zooplankton. 2. The dominant large zooplankter, the copepod Eurytemora affinis, showed a consistent vertical migration pattern of daytime ascent and night‐time descent during all sampling periods – the reverse of the most common migratory pattern of zooplankton in lakes. The cladoceran Bosmina migrated in a similar way in two of the three sampling periods. Surveys taken longitudinally in the river showed similar trends for both taxa. 3. During the lateral surveys, E. affinis was significantly more abundant in the shallow littoral zone during the night than in the daytime. The combination of vertical and lateral movement patterns along with the diel distribution of zooplanktivorous fish suggest that these movements are a predator‐avoidance mechanism. 4. Sampling programmes in large rivers should consider that larger zooplankton such as E. affinis may not be randomly distributed in the river channel and behaviours such as diel vertical migration may be just as evident in river habitats as in lakes.     

A predatory use of counterillumination by the squaloid shark, Isistius brasiliensis

A number of very unusual morphological and behavioral characteristics attributed to the cookie-cutter shark, Isistius brasiliensis, may be explained by a novel use of counterillumination. Specifically, it is proposed that a band of pigment, located beneath the jaw and bounded by ventrally directed bioluminescence, acts as a lure which mimics the search image of many upward-looking pelagic predators.     

浮游动物昼夜垂直迁移机理的主要假说及其研究进展

对有关浮游动物昼夜垂直迁移(DVM)机理的实验、假说以及理论模型方面的研究进.展进行了综述。昼夜垂直迁移通常指常规迁移(傍晚上升,拂晓下降),其行为过程不仅影响浮游动物的垂直分布,而且也间接地影响其水平分布及生活史特征,对浮游动物在一定水域的种群维持和补充具有重要的意义。与垂直迁移机理有关的假说主要有光驱动假说、逃避捕食者假说、能量和资源利用假说等,其中逃避捕食者假说已得到大量的实验证实。其理论模型研究一般在两个时间尺度上进行,一个是短期的行为机制研究,另一个从长期的生活史策略的角度考虑。随着实验技术的进步和理论及建模工具的发展,这两个时间尺度的研究正逐渐统一到一个框架下进行。     

夏季南黄海浮游动物的垂直分布与昼夜垂直移动

对 2 0 0 1年 8月南黄海青岛外海至济州岛断面 ,浮游动物的日垂直变化、断面垂直分布及其与海区水文特征的关系进行了研究。共鉴定浮游动物 40种。断面浮游动物的平均丰度为 13 62 ind/ m 3 ;种类丰富度与暖水种数呈正相关 ,分布趋势为测区东部高、西部低 ;优势种为中华哲水蚤 (Calanus sinicus)、小拟哲水蚤 (Paracalanus parvus)、拟长腹剑水蚤 (Oithona similis)、强壮箭虫 (Sagitta crassa)、近缘大眼剑水蚤 (Corycaeus affinis)。在不同水层 ,浮游动物丰度分布不同 ,随水深增加而减少 ,表层丰度最高 (3 2 2 1ind/ m3) ,温跃层和底层分别为 743 ind/ m3、43 8ind/ m3;种类组成也不相同 ,表层数量最多的种类为鸟喙尖头(Penilia avirostris)、温跃层及其以下水体为中华哲水蚤 ,其它主要种类亦表现不同水层取向。在连续观测站 ,根据浮游动物主要种类的昼夜垂直移动与温跃层关系 ,将之分为表层分布 ,近温跃层分布 ,底层分布及全水层分布 4种类型     

Antipodean white sharks on a Mediterranean walkabout? Historical dispersal leads to genetic discontinuity and an endangered anomalous population

The provenance of white sharks (Carcharodon carcharias) in the Mediterranean is both a conundrum and an important conservation issue. Considering this species's propensity for natal philopatry, any evidence that the Mediterranean stock has little or no contemporary immigration from the Atlantic would suggest that it is extraordinarily vulnerable. To address this issue we sequenced the mitochondrial control region of four rare Mediterranean white sharks. Unexpectedly, the juvenile sequences were identical although collected at different locations and times, showing little genetic differentiation from Indo-Pacific lineages, but strong separation from geographically closer Atlantic/western Indian Ocean haplotypes. Historical long-distance dispersal (probably a consequence of navigational error during past climatic oscillations) and potential founder effects are invoked to explain the anomalous relationships of this isolated 'sink' population, highlighting the present vulnerability of its nursery grounds.     

稳定同位素技术在鲨鱼摄食和洄游行为研究中的应用

随着稳定同位素分析技术的不断成熟,其在生态学领域中的应用也增长迅速,并成为动物摄食生态学的重要研究工具.鲨鱼因其在生物系统进化过程中的独特地位和海洋生态系统中的重要作用已成为海洋食物网研究的重点,然而国内针对鲨鱼摄食习性和洄游行为等方面的研究仍处于起步阶段.本文在总结了国内外鲨鱼稳定同位素分析组织样品选取和样品预处理方法的基础上,系统归纳了稳定同位素技术在鲨鱼摄食生态学,尤其在其摄食和洄游行为研究领域中的应用,着重分析稳定同位素技术在鲨鱼稳定同位素判别值和更新速率、食性分析、营养级评估、洄游路径分析和生态位分布等核心问题上的应用现状和发展前景,以期为国内学者开展鲨鱼类基础生物、生态学研究提供有益参考.