Southern elephant seal trajectories, fronts and eddies in the Brazil/Malvinas Confluence

This study describes the association between transient, mesoscale hydrographic features along the axis of the Brazil–Malvinas Confluence, in the SW Atlantic, and the foraging behavior of 2–3-year-old (focal) juvenile southern elephant seals, Mirounga leonina, from Península Valdés, Argentina. Departing from the dominant pattern of foraging on predictable bathymetric fronts on the Patagonian shelf and slope, three females out of 12 satellite-tracked juveniles remained at the edge of young warm-core eddies and near the outer core of cold-core eddies, coinciding with the most productive areas of these temperature fronts. Seal trajectories along high-temperature gradients were always consistent with the speed and direction of surface currents inferred from the temperature distribution and confirmed by surface drifters. Movements of foraging seals were compared with those of surface drifters, coinciding in time and space and yielding independent and consistent data on regional water circulation parameters. The diving pattern recorded for one focal seal yielded shallower dives and a loose diel pattern in the eddy, and a marked diurnal cycle compatible with foraging on vertically migrating prey in the cold waters of the Malvinas Current. Pre-reproductive females that use the mesoscale fronts of the Argentine Basin as an alternative foraging area would benefit from lower competition with more experienced seals and with other top predators that reproduce along the coast of Patagonia.     

Intra-archipelago moult dispersion of southern elephant seals at the Prince Edward Islands,southern Indian Ocean

During three summer surveys at Prince Edward Island (PEI), southern Indian Ocean (2001, 2004 and 2008), 416 southern elephant seals Mirounga leonina were inspected for identification tags. In all, 42 seals that had been tagged as weaned pups at their natal site were found on Marion Island (MI), 38 of which could be individually identified by resighting their tag numbers. The majority of the MI-tagged seals were yearlings or subadults, and all but one were hauled out at PEI for the annual moult. The attendance rate of the known individuals at their natal island during the annual moult was only 40%, based on their resighting histories. This was significantly lower than the 77 ± 6% moult attendance rate estimated for a random MI population sample drawn from the same cohorts (based on 10 000 replications). Annual resight probabilities (considering all haulout phases) was 58% per annum for the MI seals seen at PEI, and 80 ± 4% for the simulation. Seasonal and annual absences of seals from MI violate the ‘homogeneity of capture’ assumption of mark-recapture models. When multiple sightings during any year are treated as a single sighting, resights during other haulouts (e.g. breeding) compensate only partially for absences during the moult. Therefore, mark-recapture studies undertaken in archipelagos should ideally include both marking and resighting of individuals on all islands which will allow discrimination between mortality and local migration.     

Review of the current distribution of southern elephant seals in the eastern South Pacific

The eastern South Pacific southern elephant seal population was extinguished by extensive hunting and the current presence of this species in this area is not well understood. We reviewed existing records from the 1900s to 2014 in the eastern South Pacific, as well as tagged seals and movement records in order to assess the potential immigration source of these individuals. A total of 409 confirmed sightings were compiled, ranging from the southern tip of South America (Cape Horn Archipelago) as far north as Ecuador, including some oceanic island groups. The evidence shows also that recolonisation of its former Pacific distribution has started, with slow population growth in three incipient pupping sites in southern Chile (south of 51°S). Although the source of all of the individuals in the growing colonies is unknown, evidence from tags and satellite tagging indicates that some seals come from subpopulations on the Peninsula Valdes and the Falkland/Malvinas Islands, although mtDNA analysis showed, preliminarily, a greater genetic relationship only with the Falkland/Malvinas Islands rookery.     

黑鱾消化系统的形态学及组织学研究*

鱼类消化系统的组织结构特点与食性密切相关。为了探究岛礁性鱼类黑魢的消化生理特点, 文章以黑鱾(Girella leonina)为研究对象, 采用苏木精-伊红(H.E)染色法研究其消化系统的组织结构特点, 探讨其组织结构特点与食性、环境适应性之间的相关性。结果显示: 1) 食道向腔内形成纵向6个粗大皱褶, 该皱褶具明显横纹肌, 扩张性较强, 黏膜上皮间分布着黏液细胞, 呈锥形; 2) 黑鱾为“V”形胃, 可分为贲门部、胃体部和幽门部3个部分, 胃腺横切面为圆形, 管腔由数个腺细胞围成, 胃肌层平滑肌层极厚, 为内环肌层外纵肌层结构, 其中胃体部固有层处胃腺最为发达, 胃黏膜形成许多皱襞, 幽门胃具多级分枝皱褶; 3) 幽门处分布有150多条分枝状盲囊, 盲囊腔内充满黏膜褶, 黏膜上皮由单层柱状上皮细胞组成, 不具有杯状细胞; 4) 肝脏分为左右两叶, 组织结构呈现出一般硬骨鱼类的共性, 肝细胞体积较大, 呈多边形, 大小约为30μm; 5) 肠道具有4个肠曲, 比肠长值约为1.52±0.06, 介于植食性和肉食性鱼类之间, 整个肠道均有大量杯状细胞分布, 肠道内具发达的小肠绒毛凸起, 绒毛基部上皮向固有层内陷形成肠腺, 腺体开口于相邻绒毛基部之间, 前中肠作为主要消化吸收场所, 其绒毛数量和高度要大于后肠。文章研究了黑鱾消化系统组织学特征与其消化、吸收的关系, 认为黑鱾消化系统具备典型杂食性鱼类消化系统的特征。     

南象海豹(Mirounga leonina)喉的形态解剖和测量

对一头雌性南象海豹的喉做了解剖和测量。喉骨架由11块软骨构成:一块会厌软骨,一对杓状软骨,一块甲状软骨,一块环状软骨和三对小角状软骨,这些软骨与韧带纤维膜、肌肉组成了喉。喉室内有声带,这与鲸类,海牛类的喉室有明显差别。     

黑鱾精子发生过程中的超微结构变化

利用透射电镜对黑鱾Girella leonina精子发生过程中的各个阶段细胞以及精子的超微结构变化进行了观察.结果表明:1)黑鱾的精子发生过程主要经历了初级精原细胞、次级精原细胞、初级精母细胞、次级精母细胞、精子细胞和精子6个阶段.由精子细胞形成成熟精子还需经过前、中、后期的一系列变态过程.2)各阶段生精细胞以初级精原细胞体积最大,大小约为10.00μm×6.40μm,核大小约为8.801μm×5.80μm,而精子细胞体积最小,大小约为3.20μm×2.60μm,核约为2.80μm×2.50μm;随着生精细胞不断分裂和成熟,细胞的体积逐渐减小,核的位置、核仁、线粒体等发生相应的变化,核内染色质趋于浓缩,电子密度增加,染色程度也逐步加深.3)线粒体是各期细胞内的最主要细胞器之一,在精子发生过程中,它的数量逐渐减少,至成熟精子形成时,核内仅存4个线粒体,但体积却不断增加,内嵴变得长而明显.4)与大多数硬骨鱼类精子特点相似,黑纪的成熟精子不具顶体,核后窝深,精子的鞭毛细长,两旁具侧鳍.尾部为典型的"9+2"型结构.     

Natal site fidelity by breeding female southern elephant seals in relation to their history of participation in the winter haulout

Of the four types of terrestrial haulout periods undertaken by southern elephant seals Mirounga leonina, only the purpose of the winter haulout is unknown. Returning to a haulout site from distant pelagic foraging grounds bears significant costs in terms of increased energy expenditure, reduced foraging time and increased exposure to predation; therefore, each haulout must serve a purpose. We examined the hypothesis that the winter haulout serves to maintain familiarity with the natal site, thereby increasing site fidelity. To this end, we analysed a long-term mark-recapture dataset for female southern elephant seals at Marion Island, Southern Ocean. Results indicate that, whereas greater natal site fidelity as primiparous females was associated with recorded presence ashore at the study site during the winter haulout as immatures, this was not the case for multiparous females. Furthermore, recorded presence ashore during both the moult haulouts as immatures, and all haulouts as immatures, irrespective of haulout type, was also associated with increased site fidelity. This suggests that any haulout at the natal island as an immature seal, whether for the moult or winter haulout, assists in maintaining site fidelity. Therefore, while the winter haulout facilitates greater natal site fidelity, whether this is the sole reason for this terrestrial period remains uncertain.     

Population dynamics of southern elephant seals: a synthesis of three decades of demographic research at Marion Island

Southern elephant seal Mirounga leonina numbers declined precipitously throughout most of their circumpolar distribution since the 1950s. A long-term intensive demographic programme was initiated in 1983 on the relatively small population of southern elephant seals at sub-Antarctic Marion Island in an attempt to identify causative mechanisms associated with this decline. Weaned pups have been tagged annually since 1983, and this has produced a large number of individuals of known identity. A regular resighting programme yielded a mark-recapture dataset that has been subjected to numerous survival-based models. This ongoing programme produced a substantial body of scientific literature on population growth patterns, vital rates (survival and fecundity) and population regulation in southern elephant seals, which are reviewed in this synthesis. We briefly describe the analytical framework common to much of the demographic research, highlight important conclusions concerning population regulation of elephant seals at Marion Island, and discuss priorities for future research.