Bottom-up forcing and the decline of Steller sea lions (Eumetopias jubatus) in Alaska: assessing the ocean climate hypothesis

Declines of Steller sea lion (Eumetopias jubatus) populations in the Aleutian Islands and Gulf of Alaska could be a consequence of physical oceanographic changes associated with the 1976–77 climate regime shift. Changes in ocean climate are hypothesized to have affected the quantity, quality, and accessibility of prey, which in turn may have affected the rates of birth and death of sea lions. Recent studies of the spatial and temporal variations in the ocean climate system of the North Pacific support this hypothesis. Ocean climate changes appear to have created adaptive opportunities for various species that are preyed upon by Steller sea lions at mid‐trophic levels. The east–west asymmetry of the oceanic response to climate forcing after 1976–77 is consistent with both the temporal aspect (populations decreased after the late 1970s) and the spatial aspect of the decline (western, but not eastern, sea lion populations decreased). These broad‐scale climate variations appear to be modulated by regionally sensitive biogeographic structures along the Aleutian Islands and Gulf of Alaska, which include a transition point from coastal to open‐ocean conditions at Samalga Pass westward along the Aleutian Islands. These transition points delineate distinct clusterings of different combinations of prey species, which are in turn correlated with differential population sizes and trajectories of Steller sea lions. Archaeological records spanning 4000 yr further indicate that sea lion populations have experienced major shifts in abundance in the past. Shifts in ocean climate are the most parsimonious underlying explanation for the broad suite of ecosystem changes that have been observed in the North Pacific Ocean in recent decades.     

Linking human activity and ecosystem condition to inform marine ecosystem based management

相似文献   

Local and remote physical processes driving variability of the planktonic system in the Juan Fernández Archipelago: A multidisciplinary framework providing conservation insights

1. The Juan Fernandez Ridge, a vulnerable marine ecosystem located far off the coast of central Chile and formed by several seamounts, guyots and three islands (Robinson Crusoe, Santa Clara and Alejandro Selkirk), has recently been declared a Coastal Marine Protected Area of Multiple Uses with several National Parks embedded in it.
2. Recent studies have highlighted the influence of remote and local oceanographic structures on the hydrographic dynamics of this ridge. However, there is still a gap in understanding how they affect the structure and dynamics of the surrounding insular planktonic communities.
3. A hydroacoustic and oceanographic survey was conducted during the austral spring (October 2016), including hydrographic and zooplankton sampling around Robinson Crusoe Island. Oceanographic features were identified and tracked using satellite data (chlorophyll-a (Chl-a) and sea surface temperature) and modelling results.
4. Two events of Chl-a increase relative to a threshold (>0.45 mg m⁻³) were forced by different physical processes, both affecting the western side of Robinson Crusoe Island. In event A during the cruise period, Chl-a subsurface maxima were associated with the arrival of a coastal meander originating on the continental shelf off Chile (remote process); the zooplankton was dominated by copepods and salps, with an evident coastal–oceanic gradient. In event B, Chl-a maxima were linked to a local upwelling forced by the intensification of a localized SSW wind. No influence of remote eddies or local Von Kármán vortices on Chl-a distribution was observed.
5. These findings highlight the influence of remote and local physical processes on the structure of planktonic communities around Robinson Crusoe Island. Understanding the variability of these mechanisms and their effects at the base of the pelagic food web is critical in adopting an ecosystem-level approach.

     

Spatial structure and temporal patterns in a large marine ecosystem: Exploited reef fishes of the southeast United States

The continental shelf of the southeast United States forms one of North America's Large Marine Ecosystems (LME). Despite increased attention on ecosystem management, fisheries within this LME continue to be managed on a single stock basis, in part because interactions among species and environmental effects are poorly understood. Using fishery data from two different sources (recreational and commercial), we applied multivariate statistical techniques to elucidate spatial and temporal dynamics of reef fish assemblages. Spatial analyses of species composition revealed a zoogeographic boundary near Cape Canaveral, Florida, suggesting that management of reef fishes could be applied to the northern and southern regions with discrimination. Temporal analyses revealed, in general, gradual changes in species composition of landings, but with primary shifts in 1992 and again in 1999–2000. Chronological patterns, evident in these two independent data sets, bear the signature of one or more trending factors, which in this LME could include increased exploitation, spread of invasive species, habitat degradation, or climate change.     

公海深海底层渔业国际管理进展

以底拖网为代表的深海底层渔业对深海脆弱海洋生态系统的危害受到国际社会的热切关注。2003年以来联合国大会多次通过决议,呼吁各国各自并通过RFMO/As采取行动,根据预防性原则,采用基于生态系统的管理方法,评估深海底层渔业对脆弱海洋生态系统的影响,若评估表明确有重大不利影响,则应采取有效措施限制深海底层渔业以降低这种影响;FAO主要从技术角度制定了《公海深海渔业管理国际指南》,为管理公海深海渔业和保护脆弱海洋生态系统提出了技术标准和管理框架;RFMO承担着具体执行深海底层渔业管理措施和监督管理的责任,在北大西洋、地中海、南太平洋的公海和南极水域,相关RFMO已采取了暂停部分区域底拖网渔业活动、收集数据、评估底拖网对脆弱海洋生态系统的影响等措施,在北太平洋,新成立的北太平洋渔业管理委员会将公海底层渔业管理作为首要目标。环保非政府组织和部分科学家呼吁禁止公海深海底层渔业,但各国对此的立场尚不一致,产业界大多持反对立场。近期来看,尚难以全面禁止公海的深海底层渔业。中国正在发展公海大洋渔业,需对此密切关注,加强跟踪研究以支撑决策,并应发展和使用选择性渔具和对生态环境无害的作业方式,防止对脆弱海洋生态系统产生损害性影响。     

The decline of Steller sea lions (Eumetopias jubatus) in the North Pacific: insights from indigenous people,ethnohistoric records and archaeological data

A number of hypotheses have been proposed to explain the most recent decline (1977–2012) of Steller sea lions (SSL; Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands. We examined hypotheses about fisheries competition, environmental change, predation, anthropogenic effects and disease using observations of modern Aleut and archaeological, ethnohistoric and ethnographic data from the western Gulf of Alaska and Aleutian Islands. These data indicate that Steller sea lion numbers have declined and recovered repeatedly over the past 4500 years and were last at critically low numbers during the 1870s–1930s. Steller sea lions appear to have been more abundant during the cool periods – and lower during the warmer periods. Observations by local peoples, explorers, early government surveyors and biologists since the late 1800s suggest that low populations of SSL have been associated with high populations of Gadidae fishes (Pacific cod – Gadus macrocephalus and walleye pollock – Theragra chalcogramma) and are consistent with the ocean climate hypothesis to explain the decline of sea lions. They suggest that removals by people and killer whales (Orcinus orca) did not cause the sea lion declines, but could have compounded the magnitude of the decline as sea lion numbers approached low densities. Archaeological, anthropological and ethnohistorical analyses demonstrate that fluctuations have occurred in the North Pacific over hundreds to thousands of years and provide context for understanding the changes that occur today and the changes that will continue to occur in the future.     

基于Ecopath模型的五里湖生态系统营养结构和能量流动研究

根据2006年和2009年对五里湖渔业资源和生态环境调查数据,利用Ecopath with Ecosim软件,构建这两个时期五里湖生态系统能量通道模型,比较分析了实施净水渔业前后生态系统的结构和能量流动特征。模型包括大型、其他食鱼性鱼类、湖鲚、鲤、鲫、野杂鱼、鲢、草食性鱼类、大型虾蟹类、软体动物、其他底栖动物、浮游动物、沉水植物、其他维管植物、浮游植物、碎屑等17个功能组,基本覆盖了能量流动的途径。营养网络分析表明,增殖放养滤食性鱼类和贝类,扩大了五里湖生态系统的规模,增加了生态系统的发育程度和生态系统营养级ⅠⅡ的能量转换效率,滤食性生物与生态系统其他功能组生态位的重叠程度也有所增加。该系统各功能组间的联系加强且系统趋向稳定,但生态系统的物质流转速度和物质再循环的比例有所降低。     

Introduction: the coastal ecosystem complex as a unit of structure and function of biological productivity in coastal areas

Coastal seas are composed of relatively independent ecosystems, such as estuaries, rocky shores, mangroves, and coral reefs. Such individual ecosystems (IEs) are linked closely to each other by the dispersal and circulation of nutrients and organic matter and the movement of organisms, and form a coastal ecosystem complex (CEC). The CEC is understood as a unit of structure and function of coastal seas. It is characterized by a high degree of species diversity and it plays a large role in fishery and aquaculture production, as it provides important marine services for humans. This special volume compiles recent ecological studies of target species and IEs, to facilitate the conservation of coastal seas and the sustainability and production of their fisheries and aquaculture based on our understanding of the structure and function of the CEC in these environments.     

马鞍列岛人工鱼礁区鱼卵与仔稚鱼的群落结构

为了解人工鱼礁投放对鱼卵和仔稚鱼分布的影响,于2018年1月(冬季)、4月(春季)、7月(夏季)和10月(秋季)利用大型浮游生物网在马鞍列岛海洋牧场开展了4个航次的水平拖网调查。根据鱼卵、仔稚鱼的种类组成、数量分布等群落结构特征,对投礁区和未投礁区鱼卵、仔稚鱼的资源分布进行研究。结果显示,2018年在马鞍列岛海洋牧场共采集鱼卵5 642粒、仔稚鱼1 013尾,隶属于10目21科49种。鱼卵优势种为龙头鱼、短吻红舌鳎和小黄鱼;仔稚鱼的优势种为褐菖鲉、花鲈和小公鱼属未定种。投礁区和未投礁区鱼卵仔稚鱼的优势种种类组成基本一致,但是群落结构差异显著,投礁区各个季节的多样性指数、丰富度指数及均匀度指数均高于未投礁区,与未投礁区差异显著,且春季投礁区的生物多样性最高。聚类分析显示,春季鱼卵、仔稚鱼群落结构最为稳定,冬季群落结构最简单,夏、秋两季相似度较高,群落结构更复杂。研究表明,马鞍列岛海洋牧场人工鱼礁的投放对鱼卵、仔稚鱼具有一定的聚集和庇护作用,温度(T)、盐度(S)、水体浑浊度(Turb.)等海洋物理环境因子对鱼卵、仔稚鱼分布影响显著。     

基于Ecopath模型的巢湖生态系统结构与功能初步分析

为分析和掌握巢湖生态系统结构与功能的特征参数,结合2007—2010年巢湖渔业资源调查数据,应用Ecopath with Ecosim 6.1软件构建了巢湖生态系统的食物网模型。模型由16个功能组组成,包括初级生产者、主要鱼类、无脊椎动物和有机碎屑等。结果显示,巢湖生态系统食物网主要由4个整合营养级构成,系统规模总流量、总生产量和总消耗量都较大,分别为41 003.08、17 937.42和4 486.67 t/(km2·a);能量流动主要发生在Ⅱ、Ⅲ营养级间;参照Odum的生态系统成熟程度判定指标发现,巢湖生态系统高的生产量和呼吸比值(TPP/TR)和净初级生产量(NPP),以及较低的系统连接指数(CI)、系统杂食指数(SOI)、Finn's循环指数(FCI)和Finn's平均路径长度(FMPL)都表明:巢湖生态系统结构与功能的特征参数远没有达到成熟生态系统的标准,且劣于富营养化的太湖生态系统。从生态系统结构分析发现,导致巢湖生态系统退化的关键原因是浮游植物生物量、生产量过高,被生态系统利用的效率极低,从而导致生物多样性下降、食物网趋于简单、能量流动不畅。     

Distribution of the Steller sea lion Eumetopias jubatus during winter in the northern Sea of Japan, along the west coast of Hokkaido, based on aerial and land sighting surveys

Aerial and land-based sighting surveys were conducted to clarify the distribution of Steller sea lions during winter in the northern Sea of Japan, along the west coast of Hokkaido, from 2001 to 2003. Aerial surveys revealed that sea lions gathered around the Rishiri-Rebun Islands in March 2002 and 2003, and between Iwanai and Cape Obana in February 2003. Higher numbers of sea lions were also confirmed at Cape Ofuyu and Cape Kamui on the central-west coast compared to that at the haul-out sites in the 1980s on the upper-west coast in March 2002 and 2003. Additionally, fisherman observed sea lions along the coast of the Tsugaru Strait from February to May 2003, where the presence of sea lions was not reported in the 1980s. These facts suggest that sea lions have recently expanded their distribution southward. Land-based surveys at the recent haul-out sites indicated that sea lions in the central-west coast were composed mainly of adult and subadult males (average: Cape Ofuyu 75.2%, Cape Kamui 69.5%), which stayed from November 2002 to May 2003. In this area, sea lions arrived earlier and stayed longer than in the 1980s.     

Interannual variability of the South Georgia marine ecosystem: biological and physical sources of variation in the abundance of krill

Interannual variability is a characteristic feature of the Southern Ocean ecosystem, yet the relative roles of biological and physical processes in generating these fluctuations are unknown. There is now extensive evidence that there are years when there is a very low abundance of Antarctic krill ( Euphausia superba ) in the South Georgia area, and that this variation affects much of the ecosystem, with the most obvious impacts on survival and breeding success of some of the major predators on krill. The open nature of the South Georgia ecosystem means this variability has large-scale relevance, but even though there are unique time series of data available, information on some key processes is limited. Fluctuations in year-class success in parts, or all, of the krill population across the Scotia Sea can generate large changes in the available biomass. The ocean transport pathways maintain the large-scale ecosystem structure by moving krill over large distances to areas where they are available to predator colonies. This large-scale physical system shows strong spatial and temporal coherence in the patterns of the interannual and subdecadal variability. This physical variability affects both the population dynamics of krill and the transport pathways, emphasizing that both the causes and the consequences of events at South Georgia are part of much larger-scale processes.     

Evaluations of marine reserves as basis to develop alternative livelihoods in coastal areas of the Philippines

The 11 marine reserves along the Leyte Gulf,Eastern Samar, Philippines were quantified interms of reef slope composition, hard coralcoverage and standing fish biomass by manta towand transect dive survey from 1998 to 1999.Based on the assessed ecological conditions(Condition Index, CI; Coral Coverage Index,CCI; Reef Condition Index, RCI; Fish Biomass)and derived ranking, suitable small-scalealternative livelihoods (aquaculture orland-based) to be implemented nearby thesereserves were discussed and developed with theinvolvement of the local stakeholders composedof fishers, farmers, Non-GovernmentOrganization and Local Government Units, in a3-day planning workshop.The reserves' RCI (0.20 to 0.40) resulted infair (9 reserves) and poor (2 reserves)conditions as indicated by 64 to 68% ofnon-living and 32 to 36% of living slopesubstrate, CI of 0.15 to 0.54, CCI of 0.15 to0.49, and fish biomass of 1.8 to19.6 t km^-2. One reserve with the highestecological ranking was determined as a localmonitoring station to educate local fishers andfarmers. For other marine reserves with highecological conditions and located outer ofLeyte Gulf, the farming of Eucheuma sp.,Holothuria sp. and Pinctada sp. were suggested.While, rearing of Haliotis sp., Siganus sp., or Scylla sp. in mangrove-friendlyaquaculture systems, rice farming andeco-tourism were suggested for low rankingreserves. The potential benefits of theselivelihoods and the success in conserving themarine resources may enhance the quality oflife of the coastal populace if there is astrong multi-sectoral cooperation.