Larval fish distribution and retention in the Canary Current system during the weak upwelling season

The spatial distribution of fish larvae was studied in the Canaries‐African Coastal Transition Zone, outside the strong upwelling season. An onshore–offshore transition in the larval fish community structure was observed, from a coastal assemblage dominated by small pelagics (sardine, anchovy, mackerel), bounded by the upwelling front, to an offshore assemblage dominated by mesopelagic species (mainly Myctophidae, Phosichthydae, Gonostomatidae). Distribution of the neritic larvae was deeply influenced by the intense mesoscale activity found in the area, both horizontally (larvae were advected offshore but were always retained within the upwelling area) and vertically (larvae were deepened in the vicinity of two anticyclonic eddies). A combined effect of the upwelling front and a cyclonic–anticyclonic eddy dipole is likely the successful retention mechanism for these larvae. These results support the current belief that retention may be higher than previously thought in upwelling areas. Oceanic larvae were also collected in higher abundances near the front and an anticyclonic eddy. Neritic and oceanic larvae frequently showed a differentiated position in the water column, although they sometimes coexisted. Finally, larval connectivity between Islands within the Canary archipelago is suggested. The present study thus contributes to the understanding of the complex dispersal and retention processes in the Canaries‐African Coastal Transition Zone. However, results also highlight the poor knowledge of this region compared with the other three main Eastern Boundary Upwelling Systems in terms of ichthyoplankton dynamics. The importance of routine monitoring programs of commercial and non‐commercial species in the area is emphasized.     

Larval lake sturgeon production and drift behaviour in the Menominee and Oconto Rivers,Wisconsin

Lake sturgeon (Acipenser fulvescens) have been negatively impacted by barriers to migration, pollution and overharvest. Biological data such as the timing of spawning activity and larval drift have provided a better understanding of larval production success or failure on a site-specific basis. However, many river systems that serve as reproductive locations for remnant lake sturgeon populations remain understudied. The objective of this study was to compare and contrast aspects of larval lake sturgeon drift within and between the Oconto and Menominee Rivers over multiple reproductive seasons. Differences in larval drift chronology, the size of drifting larvae during the season and the cross-sectional profile of drifting individuals as a function of river velocity were evaluated. D-frame drift nets were deployed at a single transect below spawning sites in the Menominee (2012, 2013 and 2014) and Oconto Rivers (2013, 2014 and 2015). A total of 4,442 larvae were captured across all seasons. Larvae exhibited nonrandom drift profiles related to water velocity, and larvae size was related to horizontal drift location. The seasonal increase in body size of drifting larvae also differed among drift events within and between years and across rivers. This information will provide a better understanding of lake sturgeon early life history and has practical management connections including spawning site protection/enhancement and river flow mitigation.     

Spatial and temporal patterns in fish communities along the Illinois River

Abstract –  Fish abundance data from a fish population study (1957–2000) on the Illinois River, IL, USA were used to assess community structure. There was considerable variability among reaches and years, but three distinct fish communities were identified encompassing both temporal and spatial aspects. Temporal community shifts in the upper half of the river created two distinct fish communities, one prior to 1983 and the other after 1983. This is believed to be in response to improved water quality, albeit the responses were delayed for several years after policy implementation. The third group (Lower River) was spatially separated from the two upper river groups. These differences may reflect a combination of water quality (e.g., pollution) and habitat issues (e.g., geomorphology), common to many regulated rivers. Fish community responses in larger rivers may have considerable temporal lags after implementation of management or restoration activities that warrant strong consideration during any planning process.     

西江肇庆江段鱼类早期资源时空分布特征研究

2006年5～7月对西江肇庆江段鱼苗的时空分布进行了研究,结果表明:5月17日及6月1日前后该江段有苗汛发生,鱼苗密度平均值为0.83尾/m3,最大值为7.9尾/m3;鱼苗密度昼夜分布有显著性差异(n=26,P<0.01),夜间的密度比白天的高;鱼苗的种类在昼夜分布上也有明显差异,四大家鱼鱼苗的分布主要集中于夜间;鱼苗的分布具空间差异性,近岸的鱼苗密度高于江中央的。     

长江中游黄石江段三种不同类型河道中仔鱼空间分布研究

2016年6月10-15日对长江中游黄石江段三种不同类型河道(分汊型、顺直型和弯曲型)中仔鱼的空间格局进行了研究。共采集仔鱼12 331尾,隶属于5目7科25种,优势种为贝氏(Hemiculter bleekeri)(占仔鱼总数的89.4%)、鳊(Parabramis pekinensis)(占4.6%)和吻虾虎鱼属(Rhinogobius sp.)(占1.6%)。弯曲型河道仔鱼平均密度最大,为(2.34±1.10)ind/m~3;分汊型河道次之,为(1.97±2.03)ind/m~3,顺直型河道最低,为(1.79±1.19)ind/m~3。三种河道类型的仔鱼总体空间分布特征相似,在水平分布上,近岸处仔鱼密度最高(3.06±1.54)ind/m~3,江心最低(1.16±0.94)ind/m~3;垂直分布上,仔鱼密度表层(3.20±2.51)ind/m~3最高,其次为中层(1.69±1.35)ind/m~3,底层最低(1.20±1.20)ind/m~3。不同发育阶段的仔鱼分布呈现一定规律,总体上仔鱼从卵黄吸尽期开始倾向于分布在近岸处浅水区。本研究表明分汊型和弯曲型河道中的近岸水域是鱼类育幼场的主要分布区,在航道整治等涉水工程的建设中应该予以重点保护。     

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.     

Impacts of decentralized fish fingerling production in irrigated rice fields in Northwest Bangladesh

Rice field‐based fish seed production (RFFSP) has become established in parts of Northwest Bangladesh (NWB) as part of promoting improved rice‐based livelihoods. The impact of RFFSP on adopting households in terms of interactions of assets and other activities was assessed in a comparison of seed‐producing (RF; n = 60) and non‐seed‐producing (NRF; n = 58) households that were sampled randomly and ranked as poor, intermediate and better‐off. Adoption of RFFSP was not constrained by illiteracy of the household head, the size or ownership status of ponds, or lack of ownership of land or an irrigation pump. Poorer and intermediate households had smaller RF plots and lower production of fingerlings (kg per household) compared with the better‐off, although production efficiency (kg ha^?1) was higher. Restocking of fingerlings in RF household ponds increased productivity by 60% over NRF. Fish consumption of better‐off RF households exceeded NFR by 50%. Among the poor, seasonal benefits of income from sales and subsistence consumption of fingerlings were significant. Rice production in irrigated, and income in both irrigated and rain‐fed seasons was higher, and production costs lower, in riceplots producing fish than in rice‐only plots. Implications for supporting the innovation networks promoting and establishing RFFSP among rice growers, are discussed.     

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.     

Spatial distribution patterns of fish egg and larval assemblages in the lower reach of the Yangtze River: Potential implications for conservation and management

1. River fish diversity is threatened by anthropogenic environmental alteration to landscapes. The early life-history stages of fish play an important role in maintaining diversity and population recruitment and can be heavily influenced by landscape patterns. Information on temporal and spatial distribution patterns of fish eggs and larvae is also important for biodiversity conservation and management of fish resources.
2. The Yangtze River possesses a high diversity of fishes, including many commercially important species. The economy along the lower reach of the river is well developed, and most of the area is experiencing high pressure from human impacts. This section of the Yangtze River connects with the largest freshwater lake in China at the upstream end and flows into the estuary at the downstream end. These two landscape features are likely to have a significant impact upon the spatial distributions of fish egg and larval assemblages.
3. Environmental variables, fish eggs, and larval assemblages were sampled in three locations, at Hukou, Anqing, and Jingjiang, in the lower reach of the Yangtze River. The results suggest that the higher number of species and greater abundance in upstream sites reflect the critical function of connectivity of Poyang Lake with the river for fish recruitment in the lower Yangtze. The delayed bloom of larval fish, occurrence of estuarine species, and a lower species number and abundance of freshwater fish downstream reflect the influence of tidal intrusion from the estuary.
4. This study highlights the value of maintaining natural river–lakes connectivity in the Yangtze River as a conservation measure. The connected river–lake system should be designated as a priority area for fish resource protection in the lower reach of the Yangtze River. We recommend further measures to break down barriers between the river and other lakes and to restore the natural lateral connectivity of the floodplain ecosystem.

     

赤水河赤水市江段鱼卵漂流密度的昼夜变化特征

基于2011-2012年6-7月赤水河赤水市江段鱼类早期资源昼夜24 h连续采样情况,对该江段鱼卵漂流密度的昼夜变化特征进行了研究。7个昼夜共采集银（ Squalidus argentatus）、宜昌鳅（ Gobiobotia filifer）、鳜（ Siniperca chuatsi）、寡鳞飘鱼（ Pseudolaubuca engraulis）、犁头鳅（ Lepturichthys fimbriata）、四川华吸鳅（ Sinogastro-myzon szechuanensis）、长薄鳅（ Leptobotia elongata）、中华沙鳅（ Botia superciliaris）、紫薄鳅（ Leptobotia taeniops）和花斑副沙鳅（ Parabotia fasciata）10种鱼类的卵粒9099枚。结果显示,这些鱼卵漂流密度的昼夜变化特征不尽一致,其中银、四川华吸鳅、紫薄鳅和花斑副沙鳅夜间的漂流密度显著大于白天（Mann-Whitney U-tests, P＜0.05）,宜昌鳅和犁头鳅白天的漂流密度显著大于夜间（Mann-Whitney U-tests, P＜0.05）,而中华沙鳅和长薄鳅的漂流密度昼夜差异不显著（ Mann-Whitney U-tests, P＞0.05）。根据采集鱼卵所处发育期和孵化水温推算可知,银、宜昌鳅、长薄鳅、紫薄鳅、中华沙鳅和花斑副沙鳅的繁殖活动集中在白天时段,而犁头鳅和四川华吸鳅的繁殖活动主要发生在夜间时段。繁殖时间的昼夜分化可能是导致鱼卵漂流密度昼夜差异的主要原因。     

郁江梯级水电站群联合优化调度初探

2012—2013年3—9月在郁江金陵江段开展了漂流性鱼卵、仔稚鱼补充群体定点调查监测。结果显示共有鱼卵、仔稚鱼21种(类),隶属4目8科。优势种为䱗 (Hemiculter leucisculus) (22.2%)、鰕虎鱼(Gobiidae)(15.0%)、䱻属(Hemibarbus) (14.4%)、银鮈 (Squalidus argentatus) (7.2%)和银鲴(Xenocypris argentea) (5.5%)。每年流经金陵断面的卵苗总量平均为1.29×10⁸尾,以产黏性卵和沉性卵鱼类仔稚鱼为主,产漂流性卵鱼类仔稚鱼占卵苗总量的22.3%,未采集到四大家鱼鱼卵和仔稚鱼。卵苗发生在5—8月,以6月为盛期,月平均卵苗密度达0.041 4 ind·m^–3。鱼卵密度、仔稚鱼总密度与径流量之间具有极显著正相关关系(P<0.01,n=270),径流量与䱗、银鮈、䱻属仔稚鱼密度之间也存在显著正相关关系(P<0.05,n=270)。与历史资料对比,郁江鱼类产卵场功能发生了较大的变化,四大家鱼产卵场基本消失,仅赤眼鳟(Squaliobarbus curriculus)、鲮(Cirrhinus molitorella)、银鮈等小型产漂流卵鱼类还能成功补充,但资源量较小。径流量的年际波动是影响郁江中游早期资源补充的重要因素。     

Diel and seasonal abundance of fishes in the Platte River, Nebraska, USA

ABSTRACT:   The objective of the present study was to determine diel and seasonal patterns of fluvial fish composition and abundance. Electrofishing grids were used to collect fish in the Platte River at North Bend, Nebraska, USA. Sampling was started at 12.00 h and continued every 3 h for a 24-h period. More species were taken during the day than at night in the spring. In contrast, more species were taken at night than during the day in summer. In the fall, equal numbers of species were caught during the day and night. Comparisons of fish densities showed significant differences among the three seasons. Major taxa were significantly more abundant in spring, but river shiner Notropis blennius and western silvery minnow Hybognathus argyritis were more abundant in the fall. The greater nocturnal abundance of fish in summer and fall than in the spring may be due to changes in the physical and chemical characteristics during the study periods. The significance of seasonal difference in abundance of fish assemblages may indicate a response to changes in available habitats.     

Variation in larval fish communities: implications for management and sampling designs in reservoir systems

Understanding spatial and temporal patterns in larval fish distributions is important for investigating factors related to recruitment variability and for developing sampling methodologies. Variation in species diversity (Shannon index) and density (number 100 m^?3) of larval fishes from nearshore and pelagic habitats in Glen Elder Reservoir, KS, USA, was assessed during 1999 and 2000. Species diversity and densities of individual taxa were significantly higher (P < 0.05) in nearshore habitats than pelagic habitats during both years. Larval fish densities were generally higher in the year 1999 with higher spring water levels. Gizzard shad Dorosoma cepedianum (Lesueur) was the most abundant taxon in nearshore and pelagic habitats during both years. In addition, larval gizzard shad was sampled for the longest duration in the upper water column and overlapped with all taxa collected. High densities of gizzard shad in both habitats suggested that the potential for competitive interactions was high, especially given the lack of aquatic vegetation and habitat heterogeneity in littoral habitats. Most of the variation in larval fish diversity and density was because of temporal variation. If sampling effort must be limited and the purpose of sampling is to monitor larval diversity or density, attention should focus on sampling the same location over long time periods rather than across a variety of sampling locations.     

Riverine spawning,long distance larval drift,and floodplain recruitment of a pelagophilic fish: A case study of golden perch (Macquaria ambigua) in the arid Darling River,Australia

1. Pelagic spawning riverine fish (pelagophils) spawn in free‐flowing river habitats with downstream drift of eggs and larvae but the spatial scale is often unknown, and this constitutes a major ecological knowledge gap.
2. In the arid Darling River in south‐eastern Australia, the present objectives were: (i) to determine the potential downstream dispersal distance of young golden perch (Macquaria ambigua); and (ii) to evaluate whether provision of environmental water enhanced dispersal of young fish from Menindee Lakes to the lower Darling River (LDR) while also cueing further spawning in downstream lotic reaches.
3. Golden perch spawned in unregulated lotic tributaries on a flood pulse and larvae drifted or dispersed >1,600 km downstream and entered large ephemeral productive floodplain lake nursery habitats as fully scaled fingerlings.
4. Planned releases of environmental water cued golden perch spawning in the LDR and enabled juvenile fish to disperse downstream from the Menindee Lakes nursery into receiving populations in the LDR, Great Darling Anabranch, and southern Murray River, with some fish potentially completing an active migration of >2,100 km by age 1 year.
5. The Darling River case study highlights the need for a system‐scale approach to the conservation management of pelagophilic fish, along with multi‐year perennial flow strategies to improve ecosystem integrity in large rivers globally.

     

Recruitment sources for fish stocks inside a floodplain river impoundment in Bangladesh

Abstract The sources of fish recruitment in the hydrologically modified, impounded Pabna Irrigation and Rural Development Project (PIRDP) flood control and irrigation scheme in NW Bangladesh were investigated. Catches at sluice gates were analysed to determine the migratory behaviour of fish. Fish attempted to migrate through the undershot sluice gates when they were opened, both with and against the currents, and both in and out of the PIRDP. Many fish were caught by the fishermen at such locations, but it is argued that some fish were probably able to enter the PIRDP from outside. One to two percentage of fish survived the dry season at the PIRDP, mostly in the deeper, perennial water bodies, both in rivers and lakes, and both inside and outside the flood control scheme. Fewer species survived inside the scheme, and the numbers of species remaining declined as the dry season progressed. It was shown in companion papers that fish production inside the PIRDP was lower than outside in both 1995 and 1996 even though the growth and reproductive potential of individual fish were at least as good inside as outside. The apparently negative impact of the PIRDP was explained by the reduced accessibility of the scheme to some migrant fish, as reflected by the inside/outside species compositions. It was concluded that fish catches within the PIRDP are sustained mainly from recruits produced by residing annual populations, while the biodiversity of the stocks was augmented by limited recruitment of fish migrating through the sluice gates from external sources. Two management approaches were proposed for increasing recruitment to the impounded PIRDP fishery as cheap alternatives to fish stocking: the use of dry season reserves to protect the residing spawning stocks; and the management of flood control sluice gates to maximise recruitment from external sources.     

Evaluation of freshwater prawn‐small fish culture concurrently with rice in Bangladesh

An integrated aquaculture of freshwater prawn (Macrobrachium rosenbergii) and self‐recruiting small fish mola (Amblypharyngodon mola) was conducted in farmers' rice fields at Mymensingh, Bangladesh. There were four treatments with three replications. Four stocking densities, 10 000, 15 000, 20 000 and 25 000 ha^?1, of freshwater prawn were applied. The stocking density of mola was the same (20 000 ha^?1) in all treatments. During land preparation, triple super phosphate (TSP) and murate of potash (MP) were applied at the rate of 150 and 75 kg ha^?1 respectively. Urea was applied at the rate of 200 kg ha^?1 in equally distributed three installments after 16, 45 and 65 days of rice plantation. Prawns were fed with commercial pelleted feed at 3–8% body weight. All water quality parameters were found to be within the suitable range for freshwater prawn culture. There was a homogenous abundance of plankton communities in all treatments. The results of a 4‐month culture period showed that the average production of prawn ranged from 222 to 388 kg ha^?1, mola 51 to 68 kg ha^?1 and rice 2 880 to 3 710 kg ha^?1. Significantly higher production of both prawn and mola was recorded in the plots where the freshwater prawn stocking density was 15 000 ha^?1. This treatment resulted in a net profit of USD 1100 ha^?1.     

Reproductive migration of fish and movement in a series of reservoirs in the Upper Parana River basin,Brazil

This study evaluates the effectiveness of two fish passes at two hydropower dams (Canoas I and II) in the Upper Parana basin, which form part of a cascade of three reservoirs. Fish from 12 migratory species (3089 specimens) were captured during their ascending, reproductive migration and were tagged with hydrostatic tags. The recapture data (294 specimens over two consecutive years) showed that there is a strong tendency for the maintenance of ascending migration through reservoirs with fish passes but with differences in migratory activity within the same species. No eggs, larvae or juveniles of these species were found in samples collected over 5 years in the reservoirs above the fish passes. These data suggest that fish passes have contributed to the restoration of the migratory routes of adult fish but that in the absence of suitable spawning or nursery habitats for these species; they probably act as ecological traps and do not contribute to the recruitment of the species.     

珠江口鱼类群落结构的时空变化

根据1986～1987年珠江口及其邻近水域渔业资源的周年月份调查数据,运用MVSP软件包中的聚类分析和主坐标分析对珠江口鱼类群落的时空变化进行定量分析,描述珠江口鱼类群落的季节变化和区域变化特征,把珠江口从时空上划分为4个季节和5个水域,并与传统的划分方法作比较,讨论了这种分析结果的合理性。综合考虑个体数、重量、出现频率等因素,把珠江口鱼类的优势种确定为优势度大于1000的丽叶鲹、棘头梅童鱼、凤鲚、银鲳、杜氏棱鳀、带鱼、黄斑鲾和赤鼻棱鳀等8种,分析了优势种的区域和季节变化。     

长江中游洪湖段仔鱼昼夜变化特征的初步研究

为了解长江中游洪湖段仔鱼漂流的昼夜变化特征,于2015年6-7月,在该江段进行了3次昼夜连续采样调查,共采集仔鱼101 349尾,分属于6目8科22种,数量以贝■氏最多(占93.6%),其次是鳊(占4.3%)。仔鱼种类数和平均密度最大值均出现在20∶00-22∶00,分别为18种和(15.73±2.03)ind./m~3。以时间段为因素对部分仔鱼进行单因素分析检验,结果显示贝■氏(Hemiculter bleeker)、鳊(Parabramis pekinensis)、鲢(Hypophthalmichthys molitrix)、太湖新银鱼(Neosalanx taihuensis)仔鱼的漂流密度在不同时间段具有显著性差异,而子陵吻虾虎鱼(Rhinogobius giurinus)、鳜(Siniperca chuatsi)、鲤(Cyprinus carpio)在不同时间段差异不显著。聚类分析和非度量多维尺度排序(n MDS)结果显示,仔鱼出现时间段可分为昼和夜两组。光照强度和种间差异可能是引起仔鱼漂流特征昼夜差异的主要原因。研究结果表明将仔鱼漂流过程分时间段研究,对提高资源量精度评估也具有借鉴意义。     

Patterns of drift and power station entrainment of 0+ fish in the River Trent, England

Entrainment of 0+ riverine fish (mostly pelagic cyprinids) by a power station intake, and down-river drift over a nearby weir, followed the same pattern, occurring throughout the year and being greatest during the night in the first weeks of life (i.e. in summer), reaching a peak shortly after dusk. Entrainment and drift of benthic species, and of fish older than 0+, were negligible. Mortality following entrainment was 100%. Impingement of fish on the intake screens was negligible, probably because individuals larger than the screen mesh were able to escape the intake current. The species composition and length-frequencies of the drifting fish, but not their overall abundance, showed some variation with distance from the river margin. It is argued that the fish vulnerable to entrainment are those 0+ individuals which are dispersing in the river by drifting.