Characterization of the pelagic ecosystem in surface waters of the northern Gulf of St, Lawrence in early summer: the larval redfish-Calanus-microplankton interaction

In June 1989, the water column along a transect in the north-central Gulf of St Lawrence was thermally stratified (10–14^oC at the surface; 0-l^oC at 30 m). In the surface layer, nitrate and chlorophyll concentrations were very low; the mean concentration of chlorophyll a > 5 μm in the subsurface maximum was 0.26 μg1^-1. Autotrophic and (presumably) heterotrophic flagellates and dinoflagellates were the most abundant micro-plankton. In this system, redfish (Sebastes spp.) larvae and the planktonic copepod Calanus finmarchicus overwhelmingly dominated the ichthyoplankton and zoo-plankton, respectively. Redfish larvae, Calanus females and Calanus eggs were most abundant in the surface layer (0–25 m) day and night. Daily specific egg production rates of Calanus, calculated from shipboard incubations of females, approached the predicted maximal level for this species at the ambient temperature of the surface layer, indicating no or little food limitation. The redfish larvae were feeding almost exclusively on the Calanus eggs and were found in greatest abundance along the transect where Calanus egg production rates (eggs m^-2 day^-1), calculated from the product of the specific egg production rate and female concentration, were highest. The mono-specificity of the larval redfish diet and the codom-     

海州湾及邻近海域春夏季典型断面鱼类浮游生物群落的结构特征

根据2015年5―7月在海州湾及邻近海域存在空间异质性的南北两个典型断面进行的鱼卵、仔稚鱼水平拖网调查数据,采用多元统计分析等方法研究了该海域春、夏季鱼类浮游生物群落的空间变化。结果表明,本次调查共获得鱼卵33587粒,仔稚鱼713尾。出现鱼卵25种(未定种1种),隶属于14科25属,仔稚鱼13种(未定种1种),隶属于13科13属。鱼卵优势种主要是鳀(Engraulis japonicus)、多鳞鱚(Sillago sihama)、(魚銜)属(Callionymus spp.)、皮氏叫姑鱼(Johnius belengerii)、江口小公鱼(Stolephorus commersonni)和短吻红舌鳎(Cynoglossus joyneri);仔稚鱼优势种主要是(魚銜)属和斑鰶(Konosirus punctatus)。鱼类浮游生物种类组成年代际变化明显,目前以生命周期短、个体小、资源更新节律快的小型鱼种为主;研究表明,鱼类浮游生物的优势种在不同月份和断面之间存在一定变化,5、6月南北两断面优势种组成不同,7月开始出现共同优势种。从鱼类浮游生物的空间分布来看,近岸海域的丰度较高,5、6月鱼类浮游生物的平均丰度均为北面断面1高于南面断面2,7月反之。鱼类浮游生物群落在两个典型断面随月份呈现出不同特征,水深、温度和盐等海洋环境因子综合影响着春、夏季海州湾及邻近海域鱼类浮游生物群落结构。     

Distribution of the early life stages of small yellow croaker in the Yangtze River estuary and adjacent waters

The horizontal distribution of the early life stages of small yellow croaker Larimichthys polyactis in the Yangtze River estuary and its adjacent area was investigated through six ichthyoplankton surveys conducted during the period of mid-April to mid-July 2015. A total of seven eggs and 2461 larvae and juveniles of small yellow croaker were collected. Abundance of the specimens was highest in mid-May and lowest in mid-July. The composition of the different development stages of small yellow croaker varied among the six cruises, although post-flexion larvae and juveniles dominated the ichthyoplankton collection in each cruise. Specimens at different development stages showed different distribution patterns in the study area. The eggs, yolk-sac and pre-flexion larvae were mainly collected at stations with depth exceeding 30 m, while post-flexion larvae and juveniles were mainly distributed in the relatively shallow waters near to the mouth of the Yangtze River. In conclusion, the study suggested that the study area had largely lost the ecological function to support small yellow croaker spawning, although it could still serve as nursery ground for the species.     

东海生态系统中鱼卵、仔稚鱼种类组成、数量分布及其与环境因素的关系

为了解当前东海生态系统中鱼卵、仔稚鱼种类组成和数量分布的现状及其变化与物理环境因素的关系,根据2006年11月—2008年6月5个航次的鱼卵、仔稚鱼和物理环境调查资料,对鱼卵、仔稚鱼种类组成、数量分布与产卵场物理环境进行分析,探讨不同季节、不同年份鱼卵、仔稚鱼种类组成和数量分布的变化及其与物理环境的关系。结果显示,5个航次采集到74 813粒鱼卵、16 826尾仔稚鱼,共有135个种类。其中,鉴定到种的有109种,隶属于15目67科99属,还有17个种类仅能鉴定到属、6个种类仅能鉴定到科和3个种类仅能鉴定到目。2006年—2007年秋季、冬季和春季鱼卵、仔稚鱼的种类和数量随着季节变化逐渐增多;2008年春季的种类和数量较2007年春季明显偏少;2008年初夏种类的数量与2008年春季基本相近,但鱼卵的数量明显增多,仔稚鱼的数量基本相近。42种优势种类、重要种类和主要种类构成当前东海生态系统中鱼卵、仔稚鱼种类组成的主要成分。东海表层水温和盐度分布有显著的季节变化。秋、冬季表层水温锋面强度最强,春季次之,初夏最弱;锋面的位置秋季离岸最近,冬季次之,春季和初夏离岸最远,冬季偏南,初夏季节北移。表层盐度锋面主要分布在近岸区域,与岸线大致平行,其强度冬季最强,春、秋季次之,初夏季节最弱。秋、冬季节陆架深水海域的水温较沿岸海域高,鱼类生殖群体在陆架深水高温区产卵;春季和初夏季节沿岸海域明显升温,鱼类生殖群体由深水区向近岸海域进行生殖洄游,产卵场分布由陆架中部向近岸海域扩展,并在近岸海域形成了中心产卵场。鱼卵和仔稚鱼的分布与温、盐锋面和种类的温、盐属性的关系密切,主要分布在温度锋面暖水一侧,并有各自最适宜的温度和盐度范围。水温、盐度与种类的繁殖生物学特性是导致鱼卵和仔稚鱼种类组成与数量发生变化的主要因素;适宜的温度和盐度范围、锋区的辐聚和卷夹作用以及种类的生物学属性是影响鱼卵和仔稚鱼数量分布以及密集分布区形成的主要因素。     

基于线粒体COⅠ基因和形态学方法的3种梭子蟹科溞状幼体物种鉴定

为调查黄海蟹类资源情况,并识别梭子蟹科溞状幼体各阶段形态,利用2018年5月下旬至8月上旬在黄海海州湾及邻近水域的鱼类浮游生物大面综合调查获得的海洋蟹类幼体样品,基于线粒体COⅠ基因和形态学方法对梭子蟹科溞状幼体种类进行了鉴定。结果显示,春夏季调查水域共出现3种梭子蟹科幼体:三疣梭子蟹(Portunus trituberculatus)、日本蟳(Charybdis japonica)和双斑蟳(Charybdis bimaculata);线粒体COⅠ基因测序可准确识别3个物种。对3种梭子蟹溞状幼体的形态学观察结果表明,背棘与额棘形态、尾叉外缘小刺的有无可作为区分上述3种梭子蟹溞状幼体的主要形态学指标。根据3个物种幼体形态特征建立了梭子蟹科溞状幼体分类检索表,基于检索表对幼体进行分类鉴定,并选择8月上旬航次形态学鉴定的80个三疣梭子蟹溞状幼体、24个日本蟳溞状幼体、70个双斑蟳溞状幼体样品进行分子测序验证。结果表明,上述3种蟹类溞状幼体的形态学鉴定准确率分别达到93.75%、100%和97.14%,误判皆发生于溞状幼体Ⅰ期梭子蟹科3个物种之间。研究初步建立了黄海中部梭子蟹科溞状幼体形态鉴定...     

Characterizing larval swordfish habitat in the western tropical North Atlantic

Swordfish Xiphias gladius (Linnaeus, 1758) are a circumglobal pelagic fish targeted by multiple lucrative fisheries. Determining the distribution of swordfish larvae is important for indicating reproductive activity and understanding the early life history of swordfish. We identify and characterize larval swordfish distributions during peak swordfish spawning throughout the Gulf of Mexico and western Caribbean Sea with generalized additive models (GAMs) using catches of swordfish larvae during ichthyoplankton surveys in April and May of 2010, 2011, and 2012. The best fit GAM, as determined by stepwise, backward Akaike Information Criterion selection, included both physiochemical (temperature at 5 m, sea surface height anomaly (SSHA), eddy kinetic energy (EKE)), temporal (lunar illumination, hour of sampling) and spatial (location) variables, while near surface chlorophyll a concentration residuals remained as a random effect. The highest probability of larval swordfish catch occurred at sub‐surface temperatures, SSHA, and EKE values indicative of boundary currents. Standard lengths of larvae were larger further downstream in the boundary currents, despite high variability in length with location due to multiple spawning locations of swordfish near these currents. Probability of larval swordfish catch also peaked during the crescent and gibbous moons, indicating a lunar periodicity to swordfish spawning. These results suggest that swordfish may spawn during select moon phases near boundary currents that transport their larvae to larval and juvenile habitat including the northern Gulf of Mexico and coastal waters of the southeast United States.     

Observations on larval fish transport and retention on the Scotian Shelf in relation to geostrophic circulation

We draw inferences about the dynamic processes responsible for the dispersal of ichthyoplankton on small marine banks using physical and biological data derived from static point-estimates of water-mass characteristics and ichthyoplankton collected concomitantly on the central Scotian Shelf. Where the density field evolves slowly and ageostrophic forcing is weak, the near-surface geostrophic flow can be derived from hydrographic data using the dynamic height method modified for shallow seas. We assess our interpretations of larval distributions using simple particle tracking. The hydrography of the Scotian Shelf during November of 1997 was typical of late autumn, when density is determined by surface variation in salinity. Surface isopycnals generally paralleled isobaths, and there was no evidence of strong surface fronts. Sizes of larvae of pelagic origin (e.g. cod and hake) on Western Bank (sole spawning source) increased and became skewed towards larger animals (cod, 3–10 mm; hake, 5–15 mm) in water-mass (Temperature and Salinity) space along isopycnals, consistent with gradual mixing and limited transport in the geostrophic flow (i.e. retention). Conversely, larvae of benthic origin (e.g. herring, 6–25 mm) were distributed across water-mass space, consistent with multiple origins and substantial transport. Our results indicate that dispersal from small, low-energy marine banks results from the interaction of spawning location, geostrophic currents and bathymetric steering, and requires neither convergence nor larval behaviour.     

Mesoscale physical processes and the distribution and composition of ichthyoplankton on the southern Brazilian shelf break

The southern Brazilian shelf supports the largest fish stocks in the country, and studies on physical–biological processes in the ecology of ichthyoplankton have been recommended to provide a better understanding of the variability of the recruitment of fishing resources. This study is the first to examine the influence of mesoscale physical processes on the distribution of early life stages of fish in this shelf‐break region. Collections of fish eggs and larvae and measurements of temperature and salinity were made at 13 stations along cross‐shelf transects in December 1997. Myctophidae, Bregmacerotidae, Clupeidae, Synodontidae and Engraulidae were the most abundant larvae in the northern region, while Engraulidae and Bregmacerotidae prevailed further south. In situ hydrographic data, NOAA/AVHRR images and merged TOPEX/POSEIDON + ERS‐1/2 satellite altimetry taken during the cruise revealed an anticyclonic eddy dominating the shelf around 31°S. Larval fish abundance was lower at the centre of this feature, suggesting that the eddy advected poorer offshore waters of tropical origin towards the inner shelf‐concentrating the larvae around the eddy.     

The influence of diel vertical migration on zooplankton transport and recruitment in an upwelling region: estimates from a coupled behavioral-physical model

Diel vertical migration (DVM) is a common zooplankton behavior in which organisms reside in surface or near‐surface waters at night and at deeper depths during the day. In many upwelling regions, DVM reduces the transport of organisms away from the region. It is unclear, however, what role DVM plays in recruitment (the arrival of larvae or juveniles to locations where they will become reproducing adults) to upwelling regions. In this study, we estimate the influence of DVM on zooplankton transport, the level of recruitment of locally produced propagules (self‐recruitment), and sources of recruits in the upwelling region near Monterey Bay, California, by simulating the trajectories of fixed‐depth and vertically migrating organisms with a drifter‐tracking algorithm driven by climatological velocity fields from a three‐dimensional hydrodynamic model. Our simulations suggest that DVM into subsurface poleward and onshore currents during the day does not fully compensate for equatorward and offshore transport in the surface Ekman layer at night and does not retain zooplankton in the Monterey Bay region. Our simulations also suggest that DVM decreases the ability of zooplankton to return to the region after being transported away and shifts source regions for recruits closer to the bay. While DVM does not appear to substantially increase the potential for self‐recruitment to the region, this study indicates that other mechanisms, such as transport during non‐upwelling periods, continuous transport below the surface, increases in mean transport depth over time, or seasonal changes in hydrography, may still enable relatively high levels of self‐recruitment to this highly advective region.     

On 'variability' as a sampling artefact: the case of Sardinella in north-western Africa

Objective evaluation of the global impact of fisheries on ocean ecosystems may be hampered by various biases suggesting natural variability of exploited species to be stronger and more widespread than is really the case. One of these is reporting biases: papers are usually not published which show that nothing has changed. Another such bias is that much variability is fishery-induced, i.e. due to the truncation by fishing of the age composition of exploited populations. A third source of bias, emphasized here, is that resulting from sampling a migrating population with a fixed device. This bias is illustrated by contrasting the relatively stable echo-acoustic estimates of biomass of Sardinella spp. along the north-west African coast, i.e. from Morocco and Mauritania to Senegal (data from 1992–98), with the more variable estimates of biomass in the waters of each of these countries. We conclude that published reports of 'variability' in exploited species should explicitly account for the effect of migrations and other movements, especially when such reports are to be used for contrasting fisheries-induced with environmental impacts on biomass.     

Advection of anchovy (Engraulis encrasicolus) larvae along the Catalan continental slope (NW Mediterranean)

The Gulf of Lions is one of the main anchovy (Engraulis encrasicolus) spawning areas in the NW Mediterranean. During the spring, low‐salinity surface water from the outflow of the Rhône is advected by the shelf‐slope current along the continental slope off the Catalan coast. In June 2000, a Lagrangian experiment tracking these low‐salinity surface waters was conducted to assess the importance of this transport mechanism for anchovy larvae and to determine the suitability of the tracked surface waters for survival of anchovy larvae. The experiment consisted of sampling the tracked water parcel for 10 days with three drifters launched at the core of the shelf‐slope current where low‐salinity surface waters were detected. The survey was completed by sampling the surrounding waters. Anchovy larvae from the spawning area in the Gulf of Lions were advected towards the south in the low‐salinity waters. The size increase of anchovy larvae throughout the Lagrangian tracking closely followed the general growth rate calculated by otolith analysis (0.65 mm day⁻¹). However, advection by the current was not the only mechanism of anchovy larval transport. A series of anticyclonic eddies, originated in the Gulf of Lions and advected southwards, seemed to play a complementary role in the transport of larvae from the spawning ground towards the nursery areas. These eddies not only contributed to larval transport but also prevented their dispersion. These transport and aggregation mechanisms may be important for anchovy populations along the Catalan coast and require further study.     

Intra‐annual patterns of coastal larval fish assemblages along environmental gradients in the northeastern Mediterranean

To date, little is known about the larval‐fish assemblages (LFAs) in the eastern Mediterranean. The purpose of this study is to investigate the intra‐annual variations of LFAs with an emphasis on the effects of physical, chemical, biological and meteorological conditions in the gulf of Iskenderun, which is a shallow (100 m maximum depth), semi‐enclosed bay located in the northeastern corner of the Mediterranean. The gulf is under the influence of offshore waters throughout the year. The study was based on an ichthyoplankton survey program performed at 28 stations over 12 months, between November 2009 and October 2010. During the study, a total of 11,411 larval individuals belonging to 177 taxa were sampled. The jackknife estimate of maximum species richness was 225 ± 19 for the study area. The maximum larval richness (84 species) and abundance (827 larvae/10 m²) values coincided with spring bloom in April. Gobiids dominated the ichthyoplankton of Iskenderun Bay by constituting 9% of species richness and 42% of total individuals. Four LFAs were identified which were in early winter (November to January), late winter (February and March), spring (April to June) and summer (July to October). The intra‐annual variations of richness, abundance and composition of ichthyoplankton were significantly correlated with the temperature and mesozooplankton biomass. The wind conditions and thermal stratification were also significantly correlated with the composition of LFAs. In conclusion, phenology of LFAs were formed under the influence of physical and tropho‐dynamic conditions in Iskenderun Bay, Northeastern Mediterranean.     

Ichthyoplankton-based spawning dynamics of blue mackerel (Scomber australasicus) in south-eastern Australia: links to the East Australian Current

We describe findings of three ichthyoplankton surveys undertaken along south‐eastern Australia during spring (October 2002, 2003) and winter (July 2004) to examine spawning habitat and dynamics of blue mackerel (Scomber australasicus). Surveys covered ～860 nautical miles between southern Queensland (Qld; 24.6°S) and southern New South Wales (NSW; 41.7°S), and were mainly centred on the outer shelf including the shelf break. Egg identifications were verified applying mtDNA barcoding techniques. Eggs (n = 2971) and larvae (n = 727; 94% preflexion) occurred both in spring and winter, and were confined to 25.0–34.6°S. Greatest abundances (numbers per 10 m²) of eggs (1214–7390) and larvae (437–1172) occurred within 10 nm shoreward from the break in northern NSW. Quotient analyses on egg abundances revealed that spawning is closely linked to a combination of bathymetric and hydrographic factors, with the outer shelf as preferred spawning area, in waters 100–125 m deep with mean temperatures of 19–20°C. Eggs and larvae in spring occurred in waters of the East Australian Current (EAC; 20.6–22.3°C) and mixed (MIX; 18.5–19.8°C) waters, with none occurring further south in the Tasman Sea (TAS; 16.0–17.0°C). Results indicate that at least some of the south‐eastern Australian blue mackerel stock spawns during winter‐spring between southern Qld and northern NSW, and that no spawning takes place south of 34.6°S due to low temperatures (<17°C). Spawning is linked to the EAC intrusion, which also facilitates the southward transport of eggs and larvae. Since spring peak egg abundances came from where the EAC deflects offshore, eggs and larvae are possibly being advected eastwards along this deflection front. This proposition is discussed based on recent data on blue mackerel larvae found apparently entrained along the Tasman Front.     

长江口两种仔稚鱼网具的采集效率比较

为获得更为准确的数据,提高对长江口鱼类早期资源评估的准确度,本研究同时采用方形网(网口为1.0 m×2.0 m,网目1.0 mm,网衣长5.5 m)和标准网(网口为直径0.8 m圆形,网目0.5 mm,网衣长3.5 m)于2014年4—7月在长江口邻近海域采集仔稚鱼样本,分析比较这2种网具所采集仔稚鱼种类和数量差异,从而选择更适宜采集长江口水域仔稚鱼的采样网具。结果表明:1方形网采集到51种仔稚鱼,多于标准网的37种,两种网具的共有种类有34种,主要优势种组成没有明显差异;24月,前弯曲期仔鱼较多,它们个体小,容易从网眼滤出,导致网目较小的标准网的样品平均密度高于方形网;35—7月,方形网的样本平均密度高于标准网,但样本中仔稚鱼个体发育阶段组成有明显不同。标准网样本中前弯曲期仔鱼占多数,体形为细长形的日本鳀和鳅虎鱼的前弯曲期仔鱼平均密度高于方形网;方形网样品中后弯曲期仔鱼占优势,小黄鱼、日本鳀和鳅虎鱼等优势种的后弯曲期仔鱼平均密度均高于标准网。总体而言,方形网所采集仔稚鱼种类和数量的效果优于标准网;对于细长体形种类(如日本鳀),需结合不同网具以便采集到全部发育阶段个体,而体形较宽种类(如小黄鱼)可仅以方形网采集。     

Fish assemblages in the Southern California Current: relationships with climate, 1951–2008

We examined the dominant patterns of variability in the fish fauna of the southern California Current based on a principal component (PC) analysis of the California Cooperative Oceanic Fisheries Investigations ichthyoplankton data set, 1951–2008. Eighty‐six taxa were analyzed, including all ecologically dominant fish species, both exploited and unexploited. The first three PCs accounted for 20.5, 12.4 and 6.8% of the variance of the data, respectively (total: 39.7%). Each was dominated by taxa from particular adult or larval habitats. PC 1 predominantly represented the coherent response of 24 mesopelagic taxa from 10 families and was most highly correlated with long‐term trends in midwater oxygen levels. PC 2 was dominated by six of the seven most abundant ichthyoplankton taxa in the region, predominantly California Current endemics including key pelagic species (northern anchovy, Pacific sardine and Pacific hake), rockfishes (genus Sebastes) and two midwater taxa. It was correlated primarily with sea surface temperature and exhibited a significant declining trend. PC 3 was dominated by coastal and reef‐associated fishes with predominantly southerly affinities. It was positively correlated with sea surface temperature and sea level height, a proxy for diminished flow of the California Current. The taxa dominating PCs 2 and 3 mostly spatially co‐occur as ichthyoplankton. These results suggest that fish assemblages in the California Current are predominantly influenced by environmental forcing of their ocean habitats as adults or larvae, or both.     

Observed patches of walleye pollock eggs and larvae in Shelikof Strait, Alaska: their characteristics, formation and persistence

Using observations from 38 ichthyoplankton surveys conducted near Shelikof Strait, Alaska between 1979 and 1992, we characterized the horizontal distribution and spatial patchiness of the early life stages of walleye pollock ( Theragra chalcogtamma ). Lloyd's index of patchiness ranged from 3.9-6.1 for eggs and 3.9–16.2 for larvae. This index was size (age) dependent: low for eggs, high for newly hatched larvae, then decreasing through late larval stage. By the early juvenile stage, patchiness increased as pollock began to school. The percentage of larvae in a patch (defined as the percentage of larvae present at stations where larval counts exceeded the mean by one standard deviation during the given survey) varied greatly (26–92%). Larval distributions were used to deduce physical mechanisms responsible for patches. Three categories of patches were identified: those created by interaction of larvae with time-dependent currents, those in the vicinity of Sutwik Island, and those associated with eddies. Simulation experiments were utilized to examine processes influencing patch formation and the role of larval swimming. Between 5 and 6 weeks after hatching, larvae have swimming abilities that enable them to maintain a patch already created by physical mechanisms.     

The role of environmental conditions and exploitation in determining dynamics of redfish (Sebastes species) in the Northwest Atlantic

The six stocks of redfish (Sebastes spp.) in the Northwest Atlantic have been fished for the past 60 years, during which time they have also experienced considerable variability in environmental conditions. Despite their close proximity and with life‐history features characteristic of many deep‐sea fishes (long‐lived, slow‐growing, late‐maturing, relatively low fecundity), each redfish stock has displayed quite different dynamics. Some have been able to support apparently sustainable fisheries, whereas others have been forced to close. The causes of such differences are unclear. We used dynamic factor analysis to determine the relative impacts of exploitation (days fishing for redfish, days fishing for shrimp, days fished by all fisheries, catch in the redfish fishery, total redfish catch) and environment (North Atlantic Oscillation, surface temperature, salinity, shallow, middle, and deep bottom temperatures) on trends of abundance in each stock over the years 1960–2004. The results showed that a mix of exploitation and environmental variability, with various and different lag times, accounted for observed trends. The Gulf of St. Lawrence stock was affected most by exploitation. Flemish Cap and northern Newfoundland‐Labrador stocks were mostly affected by environmental factors with longer time lags than more southerly stocks. We conclude that management of redfish must take into account individual responses to exploitation and environment over the time periods during which such factors operate, often decades or more, as opposed to the usual practice of reviewing only dynamics of the past few years. Deep‐sea populations cannot be managed on the same scales as shelf fisheries.     

基于鱼卵仔鱼数据的东海中南部日本鲭产卵场分析

利用2016年4—5月在东海中南部海域的调查数据,对该海域日本鲭(Scomber japonicus)鱼卵仔鱼的分布特征进行了研究,并对产卵场的划分展开讨论及提出保护措施和管理建议。结果显示:4月,日本鲭鱼卵仔鱼主要出现在台湾海峡和东海南部海域,出现率均大于25%,但仔鱼在东海南部外海的出现率和丰度均较低,分别为5.00%和0.01个·100m-3。5月,日本鲭鱼卵仔鱼在台湾海峡的出现率和丰度均显著降低,分别下降至5.88%和0.22个·100m^-3;东海南部外海日本鲭鱼卵仔鱼的出现率和丰度则均显著升高,分别升至50%和36.48个·100m^-3,其中鱼卵集中出现在南部外海,出现率和丰度分别达到了40%和36.46个·100m^-3;东海中部外海从5月开始出现日本鲭鱼卵和仔鱼。结合历史资料,可以判断东海中南部日本鲭产卵场主要有台湾海峡、东海中南部近海、东海南部外海、东海中部外海等4个。日本鲭鱼卵丰度与表层水温呈显著相关关系(R=0.37,P<0.05),与表层盐度无显著相关关系(P>0.05);仔鱼丰度与表层水温及表层盐度均无显著相关关系(P>0.05)。结果表明,水温对日本鲭的产卵活动影响较大,随着水温的逐步升高,性腺发育速度加快,开始产卵的亲体数量也大量增加,这从鱼卵仔鱼的数量大量增加得以体现;而盐度变化对日本鲭的产卵活动影响相对较小。针对日本鲭不同的产卵场,建议制定差异化的繁殖亲体和幼鱼保护措施。     

Early life history and recruitment of black crappie (Pomoxis nigromaculatus) in two South Dakota waters

Abstract— We compared the early life history of black crappie ( Pomoxis nigromaculatus ) in Richmond (an impoundment) and Brant (a natural lake) lakes during 1994-1996. We expected variable recruitment (i. e., missing year classes) in the natural lake and more consistent recruitment in the impoundment. Larval black crappie abundance was always higher in Richmond Lake than Brant Lake. Peak abundance of larval black crappie was highest during 1994 in both waters. However, peak larval abundance did not correspond with fall trap-net catch per unit effort (CPUE) of age-0 black crappie, which was highest during 1995. Thus, recruitment of black crappie was not simply a function of the number of larvae hatched. Similar trends in catches of age-0 black crappie with the ichthyoplankton trawl and trap nets for both water bodies during 1994-1996 suggest that broad environmental factors similarly affected reproduction and recruitment in Richmond and Brant lakes.     

泉州湾浮性鱼卵和仔、稚鱼的种类和数量分布

根据2001-2002年在泉州湾海域分别进行4个季度月的调查资料，研究分析泉州湾鱼卵和仔、稚鱼的种类组成，数量和主要种类的分布。结果表明，本海区共出现鱼卵和仔、稚鱼34种，分别隶属于14科21属。在数量上，鱼卵和仔稚鱼最高值均出现在春季(5月)，其中鱼卵数量最大的种类是鳀科鱼类，约占总卵量34．2％。仔稚鱼则以鱚科鱼类最为丰富，占61．8％。在数量分布上，不论鱼卵或是仔、稚鱼均以9号站最为密集。这表明该区鱼类主要产卵期在春季。