Spatial distribution pattern and physical – biological interactions in the larval notothenioid fish assemblages from the Bransfield Strait and adjacent waters

The Bransfield Strait and adjacent waters represent one of the most important areas of larval retention off the Antarctic Peninsula. The species composition of larval fish assemblages has been described in detail in previous surveys carried out in the area, but the role of environmental parameters influencing the spatial distribution of early life stages was poorly known. By applying generalized additive models and multivariate analyses, we evaluated the role of environmental variables in shaping the small‐scale distribution of larval fish and investigated the spatial structure of the larval assemblage. It consisted of a few dominant notothenioid species, such as Champsocephalus gunnari, Lepidonotothen squamifrons, Lepidonotothen larseni, Pleuragramma antarctica and Trematomus scotti, and several other rarely caught species. Sea water temperature, salinity and sampling depth were the most important factors determining the spatial distribution of fish with different relative contributions, together explaining more than 80% of total deviance observed. Species richness was mostly affected by salinity, probably due to the narrow range of salinity preference by the species. Cluster analysis of abundance and presence data identified six and five distinct groups, respectively, each of them with substantial contributions of single or rarely two species. Differences in reproductive strategies of adult populations and spatial distribution of early life stages driven by different larval behaviour in response to environmental factors contribute to maintaining a well‐structured larval fish assemblage, ensuring spatial and food niche partitioning.     

海冰与南半球环状模对南极布兰斯菲尔德海峡南极磷虾种群结构的影响

南极磷虾(Euphausia superba)是南大洋生态系统的关键物种,其生活史各阶段的生理过程与海冰密切相关。本研究基于开放获取数据库计算了布兰斯菲尔德海峡内反映南极磷虾种群结构特征的5个参数,包括补充指数和幼体、雌性、雄性平均体长以及雌性个体占比,并结合布兰斯菲尔德海峡及周围3个水域的海冰面积、水深、海底复杂度以及南半球环状模(SAM)逐日指数构建广义加性模型,探讨了海冰与气候事件对磷虾种群动态的影响。结果表明,磷虾幼体、雄性磷虾平均体长与60日前的威德尔海西北部海域海冰面积呈显著的负相关,磷虾补充指数与当日和60日前的SAM呈显著的正相关。随着海底复杂性的增加,磷虾补充指数显著下降。4个海域的海冰面积变化对磷虾补充指数和其他种群特征指标的影响存在差异。     

Early life history connectivity of Antarctic silverfish (Pleuragramma antarctica) in the Ross Sea

A recent population hypothesis for Antarctic silverfish (Pleuragramma antarctica), a critical forage species, argued that interactions between life history and circulation associated with glacial trough systems drive circumpolar distributions over the continental shelf. In the Ross Sea, aggregations of eggs and larvae occur under fast ice in Terra Nova Bay, and the hypothesis predicted that dispersing larvae encounter outflow along the western side of Drygalski Trough. The outflow advects larvae towards the shelf‐break, and mixing with trough inflow facilitates return toward the inner shelf. To examine the hypothesis, we compared samples of P. antarctica collected near Coulman Island in the outflow, along Crary Bank in the inflow, and a third set taken over the rest of the Ross Sea. We ruled out misidentification using an innovative genetic validation. Silverfish larvae comprised 99.5% of the catch, and the highest population densities were found in Drygalski Trough. The results provided no evidence to reject the population hypothesis. Abundance indices, back‐calculated hatching dates, length distributions and growth were congruent with a unified early life history in the western Ross Sea, constrained by cryopelagic early stages in Terra Nova Bay. By contrast, a sample in the Bay of Whales revealed much smaller larvae, suggesting either a geographically separate population in the eastern Ross Sea, or westward connectivity with larvae spawned nearby by fish sourced from troughs upstream in the Amundsen Sea. These results illustrate how hypotheses that integrate population structure with life history can provide precise spatial predictions for subsequent testing.     

Antarctic silverfish: life strategies of a key species in the high‐Antarctic ecosystem

Among the endemic notothenioid fish of Antarctica, the Antarctic silverfish (Pleuragramma antarcticum) is the only species in which all developmental stages live throughout the water column. It is widely distributed in the shelf waters around the continent, inhabiting both open waters and areas of pack ice at depths from 0 to 900 m. In successfully occupying this habitat, it evolved a suite of specific biological, ecological and physiological adaptations to the environmental conditions in the cold and highly seasonal Antarctic waters. Specialization for the pelagic environment evolved over millions of years enabled life under unusual environmental constraints and colonization of the pelagic realm of the Antarctic continental shelf. A sudden change of environmental conditions driven by the current rapid climate change could negatively affect this weak equilibrium, with a catastrophic cascade effecting higher trophic levels. Indeed, as both adults and early life stages of the Antarctic silverfish appear to be strongly dependent on sea‐ice, this species would be especially sensitive to climatic or oceanic changes that reduce the extent of sea‐ice cover or the timing of formation of coastal polynyas.     

基于空间自相关模型的南极半岛北部水域南极磷虾渔场时空演变特征

南极磷虾是南极海域生态系统的关键物种,是南极渔业的主要捕捞对象,其渔场具有显著的时空分布特征.为明晰南极半岛北部水域磷虾渔场的变动情况,本研究根据中国2010—2020年南极磷虾渔业统计资料,运用全局Moran's I指数和热点分析对该水域磷虾渔场的时空分布特征进行了分析.结果显示,南极半岛北部水域磷虾渔获量在空间分布...     

基于点模式模型的南极半岛北部南极磷虾渔场的时空变动

南极磷虾作为南极生态系统中的关键物种,磷虾渔场时空演变规律对于磷虾海洋生态功能影响及其资源管理十分重要。本研究利用我国磷虾渔业生产数据,按照月份组合,针对南极半岛北部磷虾渔业,采用点模式方法,利用3个空间因子:经度、纬度和离岸距离,获得各月磷虾资源分布最佳点模式模型和模型的方差分析结果,并以最佳点模式模型推知可能潜在的渔场分布。结果显示,(1)12月磷虾渔场离岸距离最大(为45 km),随后,渔场逐渐向南设得兰群岛岸线逼近,至3月时渔场离岸最近,3月之后,磷虾渔场逐渐远离海岸线,4月和5月渔场离岸距离大约在13 km左右。(2)点模式模型的方差分析结果发现,12月,1月,3月和4月最优点模式模型对模型的方差解释率分别为59%、60%、57%和68%,空间因子能够较好拟合磷虾渔场分布,而2月和5月,空间点模型对总体方差的解释率分别为38%和32%。(3)夏季12—1月,磷虾渔场分布在乔治王岛北部;2月,在利文斯顿岛周围形成第2个渔场,以及布兰斯菲尔德海峡中部形成第3个渔场;3—5月渔场基本分布在布兰斯菲尔德海峡沿南极半岛岸线平行方向分布。研究表明,南极半岛北部磷虾渔场的离岸距离远近与该海域海冰边界消融和生长的规律相吻合;基于空间因子点模式模型在大部分月份均能较好地拟合磷虾渔场的时空演变规律,再配合单位捕捞努力量渔获量(CPUE)数据,可以作为探测磷虾群热区的潜在手段。     

2020年秋季南极布兰斯菲尔德海峡南极磷虾集群时空分布

南极磷虾是南极海洋生态系统中的关键物种,具有重要的商业开发潜力,但其集群的类型与分布存在较大时空异质性,这增加了南极磷虾资源评估的难度,也对南极磷虾渔业的海上作业与企业生产安排带来了较大的挑战.为了探究布兰斯菲尔德海峡渔场内南极磷虾的集群分布和结构特征,提高渔船作业效率,基于渔船采集的声学数据,分析其时空分布特征,昼夜...     

Larval fish assemblages and water mass structure off the oligotrophic south-western Australian coast

Larval fish assemblages were sampled using replicated oblique bongo net tows along a five‐station transect extending from inshore (18 m depth) to offshore waters (1000 m depth) off temperate south‐western Australia. A total of 148 taxa from 93 teleost families were identified. Larvae of Gobiidae and Blenniidae were abundant inshore, while larvae of pelagic and reef‐dwelling families, such as Clupeidae, Engraulidae, Carangidae and Labridae were common in continental shelf waters. Larvae of oceanic families, particularly Myctophidae, Phosichthyidae and Gonostomatidae, dominated offshore assemblages. Multivariate statistical analyses revealed larval fish assemblages to have a strong temporal and spatial structure. Assemblages were distinct among seasons, and among inshore, continental shelf and offshore sampling stations. Inshore larval fish assemblages were the most seasonal, in terms of species composition and abundance, with offshore assemblages the least seasonal. However, larval fish assemblages were most closely correlated to water mass, with species distributions reflecting both cross‐shelf and along‐shore oceanographic processes and events. Similarity profile (SIMPROF) analysis suggested the presence of twelve distinct larval fish assemblages, largely delineated by water depth and season. The strength and position of the warm, southward flowing Leeuwin Current, and of the cool, seasonal, northward flowing Capes Current, were shown to drive much of the variability in the marine environment, and thus larval fish assemblages.     

Springtime ichthyoplankton of the slope region off the north-eastern United States of America: larval assemblages, relation to hydrography and implications for larval transport

Larval transport in the slope region off north‐eastern North America influences recruitment to juvenile habitats for a variety of fishes that inhabit the continental shelf. In this study, collections of larval fishes were made during springtime over the continental slope to provide insights into larval distributions and transport. Ichthyoplankton composition and distribution mirrored the physical complexity of the region. Three larval fish assemblages were defined, each with different water mass distributions. A Gulf Stream assemblage was found predominantly in the Gulf Stream and associated with filaments of discharged Gulf Stream water in the Slope Sea. Larvae of this assemblage originated from oceanic and shelf regions south of Cape Hatteras. Several members of this assemblage utilize habitats in the Middle Atlantic Bight (MAB) as juveniles (Pomatomus saltatrix, Peprilus triacanthus) and other members of the assemblage may share this life cycle (Mugil curema, Sphyraena borealis, Urophycis regia). A Slope Sea assemblage was found in all water masses, and was composed of epi‐ and mesopelagic fish larvae, as well as larvae of benthic shelf/slope residents. Larvae of one member of this assemblage (U. tenuis) are spawned in the Slope Sea but cross the shelf‐slope front and use nearshore habitats for juvenile nurseries. A MAB shelf assemblage was found in MAB shelf water and was composed of larvae that were spawned on the shelf. Some of these species may cross into the Slope Sea before returning to MAB shelf habitats (e.g. Enchelyopus cimbrius, Glyptocephalus cynoglossus). Previous studies have examined the effect of warm‐core rings on larval distributions, but this study identifies the importance of smaller‐scale features of the MAB shelf/slope front and of filaments associated with Gulf Stream meanders. In combination with these advective processes, the dynamic nature of larval distributions in the Slope Sea appears to be influenced, to varying degrees, by both vertical and horizontal behaviour of larvae and pelagic juveniles themselves.     

基于物种分布集成模型的布兰斯菲尔德海峡南极磷虾栖息地研究

南极磷虾为南大洋海洋生态系统中的关键物种,但目前关于该物种栖息地研究仍较为有限,这不利于对该物种分布的理解以及资源管理.实验利用南极磷虾资源密度数据与海表面温度、海表面叶绿素、海表面高度、净初级生产力和季节性海冰覆盖等5个环境因素,通过12种算法的集成模型对南极磷虾栖息地进行分析.结果显示,支持向量机、随机森林、多元自...     

Entrainment of larval fish assemblages from the inner shelf into the East Australian Current and into the western Tasman Front

Entrainment and transport of larval fish assemblages by the East Australian Current (EAC) were examined from the coastal waters of northern New South Wales (NSW) to the western Tasman Front, via the separation of the EAC from the coast, during the austral spring of 2004. Shore‐normal transects from the coast to the EAC off northern NSW revealed an inner shelf assemblage of near‐shore families (Clupeidae, Engraulidae, Platycephalidae and Triglidae), an EAC assemblage dominated by Myctophidae and Gonostomatidae, and a broadly distributed assemblage over the continental shelf dominated by Scombridae and Carangidae. Further south and after the EAC had separated from the coast, we observed a western Tasman Front assemblage of inner shelf and shelf families (Clupeidae, Engraulidae, Serranidae, Scombridae, Carangidae, Bothidae and Macroramphosidae). The abundance of these families declined with distance from the coast. Surprisingly, there was no distinctive or abundant larval fish assemblage in the chlorophyll‐ and zooplankton‐enriched waters of the Tasman Sea. Water type properties (temperature‐salinity, T‐S), the larval fish assemblages and family‐specific T‐S signatures revealed the western Tasman Front to be an entrained mix of EAC and coastal water types. We found an abundance of commercially important species including larval sardine (Sardinops sagax, Clupeidae), blue mackerel (Scomber australasicus, Scombridae) and anchovy (Engraulis australis, Engraulidae). The entrainment and transport of larval fish from the northern inner shelf to the western Tasman Front by the EAC reflects similar processes with the Gulf Stream Front and the Kuroshio Extension.     

Larval and early juvenile fish dynamics in main channel and backwater lake habitats of the Illinois River ecosystem

The spatial and temporal complexity of large river ecosystems likely promotes biological diversity within riverine larval fish assemblages. However, the focus of most previous riverine studies of larval fish distribution has tended to concentrate mainly on backwater habitats. There has been less focus on the value of the main channel for larval fishes. We sampled two habitats types (three main channel sites and three backwater lakes) along 20 km of the Illinois River ecosystem during 2 years to compare the larval fish distribution along both spatial and environmental gradients between these habitats. Across the 2 years of this study, we found similar trends in the spatial and temporal distribution of larval fish, although there were some differences in densities between years. The relative abundance and size of many of the different fish taxa varied among habitats. Centrarchids, clupeids, poeciliids, cyprinids (excluding common carp) and atherinids were more abundant within backwater lake habitat. In contrast, common carp (Cyprinus carpio), sciaenids, moronids and catostomids were more abundant in main channel habitats. Furthermore, sciaenid and clupeid larvae captured in the backwater lake habitat were larger as the season progressed than those captured in the main channel. Our study suggests that larval fish show habitat specialisation, similar to adults, indicating that both the backwater lakes and the main channel are both important for larval fish and preserving the diversity of the fish assemblages in large floodplain rivers.     

夏季台湾海峡北部及邻近海域鱼类群落结构及环境解释

根据2014年7月台湾海峡中部、北部及邻近水域渔业资源底拖网调查资料,分析了该水域的鱼类群落结构,包括种类组成、区系特点、优势种、多样性及空间分布等,探讨了鱼类群落结构与环境因子的关系,并阐述了鱼类群落的群聚结构。结果表明,调查海域共捕获鱼类84种,隶属于16目、48科、69属。从种类数上看,适温类型以暖水种为主,区系类型以大陆架浅水底层鱼类以及大陆架岩礁性鱼类为主;从生物量组成上看,区系类型则以大陆架浅水中低层鱼类为主。优势种为带鱼(Trichiurus japonicus)和七星底灯鱼(Benthosema pterotum),合计渔获质量占总渔获质量的46.92%,对总渔获质量的回归贡献值分别为0.30和0.62;高生物量区集中分布在台湾海峡北口海域,在空间上表现为明显的生态位重叠。层次聚类分析将群落优势物种划分为2个主要的生态类型:沿海类型和广布类型,沿海类型的代表性物种包括龙头鱼、黄鲫、鳓;广布类型物种有带鱼、窄颅带鱼、七星底灯鱼、竹荚鱼、刺鲳、麦氏犀鳕。Shannon-Wiener多样性、Pielou均匀度和Margalef丰富度的变化范围分别为0.22~2.31、0.11~0.72、0.36~4.04,平均值分别为1.44、0.51、1.59,丰富度与总渔获质量表现为显著负相关(r=?0.65),与深度显著正相关(r=0.48)。物种?环境典范对应分析表明,与物种空间结构关系密切的影响因子为底盐、底层无机氮、底温、表底温差和水深;而影响群落优势群体分布的因子为底温、底盐和底层无机氮。     

Influence of mesoscale eddies on ichthyoplankton assemblages in the Gulf of Alaska

Mesoscale eddies (100–200 km in diameter) propagating along the shelf‐break in the Gulf of Alaska are ubiquitous and have been shown to influence the ecosystem, but their influence on ichthyoplankton species composition and diversity has not been described. Evidence for larval fish entrainment in these eddies was examined using data from a cruise in 2005 that sampled three eastern Gulf of Alaska mesoscale eddies, and sampling that compared shelf to slope ichthyoplankton assemblages in the northern Gulf of Alaska (2002–2004). Hierarchical cluster analysis of oceanographic data showed that stations grouped according to location within an eddy. Species hierarchical cluster analysis revealed a latitudinal turnover in species composition, and an abundant species group. Species richness was correlated with distance from eddy center (P = 0.00025), and assemblages within eddies were significantly different (P < 0.05) from those in surrounding basin and shelf waters. These results suggest that mesoscale eddies propagating along the continental shelf‐break influence larval fish assemblages over the shelf and slope, which has implications for the timing and extent of larval fish distribution in the Gulf of Alaska.     

Modeling the egg and larval transport pathways of the Antarctic toothfish (Dissostichus mawsoni) in the East Antarctic region: New insights into successful transport connections

The Antarctic toothfish (Dissostichus mawsoni) is an important fishery species widely distributed in the Southern Ocean, especially in areas covered by sea ice. Understanding fish distributions and life cycles, including the transport and survival of eggs and larvae, is essential for the assessment and sustainable management of the fishery. However, owing to difficulties with in situ winter observations, information on the early life stages of D. mawsoni is lacking. Here, we investigated the transport pathways of fish eggs and larvae through a particle tracking study, using satellite-derived ocean surface velocities in the East Antarctic region, which includes important D. mawsoni habitats and exploratory fisheries. Our results indicate that particles released from continental slopes are more likely to be successfully transported to suitable settlement grounds than those released from the BANZARE Bank (the southern region of the Kerguelen Plateau), which is situated further north and has been hypothesized to be a potential spawning ground for D. mawsoni. This study demonstrates successful source–settlement connections in relation to ocean recirculation and suggests important settlement regions for D. mawsoni larvae in the East Antarctic region.     

Larval fish assemblages along the south-eastern Australian shelf: linking mesoscale non-depth-discriminate structure and water masses

We present findings of the first mesoscale study linking larval fish assemblages and water masses along shelf waters off south-eastern Australia (southern Queensland-New South Wales), based on vertical, non-depth discriminate data from surveys in October 2002 and 2003 (spring) and July 2004 (winter). Clustering and ordination were employed to discriminate between larval assemblages and, for the first time, to define water masses from water column temperature frequencies. Surveys yielded 18 128 larval fishes comprising 143 taxa from 96 identifiable families, with small pelagics accounting for 53% of the total. Three major recurrent larval assemblages were identified during the study, each of which matched one of three water masses, namely East Australian Current to the north (EAC; 20.5–23.4°C), Tasman Sea to the south (TAS; 14.8–17.5°C), and mixed EAC–TAS water in between (MIX; 18.3–19.9°C). All three assemblages were present in spring, whereas only EAC and MIX occurred in the more northerly constrained winter survey. Furthermore, boundaries between the EAC, MIX and TAS assemblages were found to be dynamic, with locations shifting temporally and spatially depending on EAC extent. Assemblage composition differed significantly between water masses across surveys, with EAC–TAS being most dissimilar. Such contrast was due to the presence of tropical/temperate taxa in EAC, primarily temperate-associated taxa in TAS, and a combination of EAC–TAS taxa within MIX consistent with the convergence of both waters. Results highlight the strength of employing larval assemblages as indicators of water masses, particularly in view of the potential effect of climate change on spawning habitats of shelf fishes.     

采用声学方法研究2016年秋季布兰斯菲尔德海峡南极磷虾群昼夜垂直移动特征及其影响因素

近年来,南极磷虾渔业过于集中于布兰斯菲尔德海峡,这也使得该海区磷虾资源状况及其生态学特征日益受到关注。南极磷虾群具有较为明显的昼夜垂直移动特征,开展此方面的研究可为探索其渔场形成机制提供基础数据,并为磷虾渔业反馈式管理提供参考。基于磷虾渔船上Simrad EK80记录的相关声学数据,使用Echoview软件判别声学数据中的磷虾群体,对2016年秋季布兰斯菲尔德海峡南极磷虾群昼夜垂直移动特征进行分析,并进一步分析影响磷虾群昼夜垂直移动的因素。结果显示,3月和4月磷虾群深度基本维持在250 m以浅,虾群最大深度出现在日升时分的频次最高（22.9%）,而最浅深度出现在夜间时分的频次最高（36.0%）,同时在日升时分,虾群厚度达到最大值;白天磷虾群多集中在较深水层,夜间会上浮到较浅水层。随着月份的推移,磷虾群平均深度总体呈现加深的趋势。光强和海底深度是影响磷虾群深度变化的2个主要因素。     

Dynamic regulation of larval fish self‐recruitment in a marine protected area

The factors that regulate the self‐recruitment of fish larvae were explored in Cabrera National Park (CNP), an insular Marine Protected Area (MPA) located off southern Mallorca (Western Mediterranean). Our study attributes the regulation of larval arrival to the MPA to a combination of retention by topographically generated circulation patterns around the island and shelf break frontal dynamics. Specifically, within the shelf, interaction of the wind‐induced oscillatory flow with the island was shown to generate ephemeral recirculation patterns that, over time, favor larval retention in the proximity of the MPA. According to our measurements, oscillatory flows produced by wind‐forced island‐trapped waves (ITWs) dominate the flow around CNP. ITW‐forced dispersion simulations were in agreement with the observed distributions of several typical fish species that breed in the CNP. A second regulator of environmental variability is the influence of boundary currents and open ocean mesoscale structures at the shelf break. These structures generate frontal zones that are comparatively more long‐lived than inner‐shelf circulation patterns, and they were shown to act as barriers to the offshore dispersion of coastal fish larval assemblages. Finally, inferences from larval size distributions around the MPA together with particle‐tracking model simulations suggested the relevance of behavioral processes for larval recruitment to the MPA. Based on these observations, the waters around the CNP can be viewed as a relatively stable system that allows breeding fish populations to rely on self‐recruitment for their long‐term persistence, independent of other source populations along the coast of Mallorca.     

Spatial distribution of Antarctic minke whales (Balaenoptera bonaerensis) in relation to spatial distributions of krill in the Ross Sea,Antarctica

The spatial distribution of Antarctic minke whales in the Ross Sea with relation to spatial distributions of their prey – krill – was investigated in this study using generalized additive models (GAMs). Spatial distributions of two species of krill (ice and Antarctic krill) were estimated by GAMs. Three abiotic factors – distance from the continental shelf break (800 m isobaths), the mean temperature and salinity from the surface to 200 m (MTEM‐200 and MSAL‐200), and latitude and longitude – were used as covariates for models of krill. Estimated spatial distributions of krill were then used with other covariates to model the spatial distribution of Antarctic minke whales. In the selected model of Antarctic minke whales, Antarctic krill were more influential than ice krill. The number of Antarctic minke whales increased as the density of Antarctic krill increased to around 1.5 g m^?2. Beyond that, the number of Antarctic minke whales decreased as the density of Antarctic krill increased. High densities of the Antarctic minke whales were estimated along the sea ice edge in the eastern part of the Ross Sea. Specifically, the densities were high in the north of the continental shelf break where low MTEM‐200 and MSAL‐200 and intermediate densities of Antarctic krill were observed. Further data collection is needed to investigate interannual variations and trends in their relationship. The results show that the spatial distribution of Antarctic minke whales is a function of longitude, distance from the shelf break, oceanographic condition (temperature and salinity), and densities of ice and Antarctic krill.     

Improvement in the efficiency of stocking lakes with larvae of Coregonus albula L. by delaying hatching

Low survival of vendace (Coregonus albula) eggs incubating on natural spawning grounds (due to silting, oxygen deficits and action of predators) is discussed as one of the reasons for the great fluctuation in numbers of commercial fish. Incubation of eggs in hatcheries where the survival rate averages 60% could compensate for the great numerical disparity between the eggs spawned naturally and those taken for hatcheries. In the absence of the effects of mass stocking of lakes with vendace larvae, one can conclude that apparent mortality during the larval stage also determines the strength of the successive year-class.Vendace larvae are usually stocked immediately after the ice cover recedes from lakes. At this time they often face a period of cold weather when water temperature is low and food organisms are scarce. Poor environmental conditions cause slow growth of larvae. This increases the period of highest vulnerability of the larvae to predation.It is possible to accelerate the growth of larvae by synchronizing the time of stocking with the development of favourable thermal conditions and food availability in lakes. In Polish climatic conditions the first 10 days of May seem to be a suitable time for stocking lakes.A technique for delaying vendace egg hatching by cooling the hatchery water has been developed. It enables hatching of vendace to be delayed from the beginning of April until the beginning of May, thereby inducing mass hatching of larvae when lake conditions are optimal for stocking.