Geographical and seasonal patterns in the diet of Cape fur seals Arctocephalus pusillus pusillus in Namibia, based on extensive scat analyses

IF 1.4 4区 生物学 Q3 MARINE & FRESHWATER BIOLOGY
DN Mwaala, MR Wilhelm, S. Kirkman, J-P Roux
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引用次数: 0

Abstract

Namibia's population of Cape fur seals Arctocephalus pusillus pusillus is a major constituent of top predator biomass in the northern Benguela upwelling system. Understanding their diet is key to comprehending their role in the ecosystem and potential drivers of recent population changes, such as a northward extension of the population's range. Using prey remnants retrieved from 1 413 scat samples collected monthly at 12 Cape fur seal colonies along the Namibian coast over 28 years (1994-2021), we assessed seasonal and geographical differences in their diet. We include the first comparison of diet between the growing colonies in the far northern area of Namibia and the colonies to the south, many of which have been in decline. Four fish species dominated in the diet. The bearded goby Sufflogobius bibarbatus, which is ubiquitous throughout the northern Benguela ecosystem, was the mostabundant prey item in the diet. However, Cape fur seals appeared to show a preference for the more-nutritious fish species Cape horse mackerel Trachurus capensis and the lanternfish Lampanyctodes hectoris by switching to those prey during autumn and spring in the north and south, respectively, coinciding with the greater availability of those species during upwelling periods. The availability of Cape horse mackerel, especially during a critical period for the growth and development of pups before the onset of winter, may be key to the greater productivity of Cape fur seal colonies in the north relative to those in the south of Namibia, and warrants further investigation. Juveniles of Cape horse mackerel and Cape hake Merluccius capensis were the only fishery species of commercial importance that were relatively abundant in the seals' diet, while the sardine Sardinops sagax, which was historically dominant, was found in negligible proportions.
根据大量粪便分析得出的纳米比亚开普海狗(Arctocephalus pusillus pusillus)饮食的地理和季节模式
纳米比亚的开普海狗(Arctocephalus pusillus pusillus)种群是本格拉上升流系统北部顶级掠食者生物量的主要组成部分。了解海狗的食性是理解它们在生态系统中的作用以及近期种群变化(如种群范围向北扩展)的潜在驱动因素的关键。我们利用 28 年(1994-2021 年)来每月在纳米比亚海岸的 12 个角海狗群落收集的 1413 份粪便样本中的猎物残留物,评估了它们饮食的季节性和地域性差异。我们首次比较了纳米比亚最北部地区不断壮大的海狗群落与南部海狗群落(其中许多海狗群落已经衰退)之间的饮食差异。四种鱼类在食谱中占主导地位。在本格拉北部生态系统中无处不在的胡须鰕虎鱼 Sufflogobius bibarbatus 是食物中最丰富的猎物。然而,开普海狗似乎更喜欢营养价值更高的鱼类物种开普马鲛鱼(Trachurus capensis)和灯笼鱼(Lampanyctodes hectoris),分别在北部和南部的秋季和春季转而捕食这些猎物,这与上升流期间这些物种更容易获得的情况相吻合。开普马鲛鱼的可获得性,尤其是在冬季来临前幼海豹生长和发育的关键时期,可能是纳米比亚北部海狗群落比南部海狗群落生产力更高的关键,值得进一步研究。开普竹荚鱼和开普无须鳕的幼鱼是海豹食物中唯一相对丰富的具有商业重要性的渔业物种,而历史上占主导地位的沙丁鱼比例微乎其微。
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来源期刊
African Journal of Marine Science
African Journal of Marine Science 生物-海洋与淡水生物学
CiteScore
2.60
自引率
16.70%
发文量
17
审稿时长
6-12 weeks
期刊介绍: The African (formerly South African) Journal of Marine Science provides an international forum for the publication of original scientific contributions or critical reviews, involving oceanic, shelf or estuarine waters, inclusive of oceanography, studies of organisms and their habitats, and aquaculture. Papers on the conservation and management of living resources, relevant social science and governance, or new techniques, are all welcomed, as are those that integrate different disciplines. Priority will be given to rigorous, question-driven research, rather than descriptive research. Contributions from African waters, including the Southern Ocean, are particularly encouraged, although not to the exclusion of those from elsewhere that have relevance to the African context. Submissions may take the form of a paper or a short communication. The journal aims to achieve a balanced representation of subject areas but also publishes proceedings of symposia in dedicated issues, as well as guest-edited suites on thematic topics in regular issues.
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