Lemon sole Microstomus kitt in the northern North Sea: a multidisciplinary approach to the early life-history dynamics

Lemon sole Microstomus kitt is a commercially valuable flatfish species that occurs in shelf waters around the northeast Atlantic. Only the most basic life-history information is available for the North Sea. Spawning is generally assumed to occur between early May and October, with a peak between May and August. Lemon sole larvae have been found in the water column in the northern North Sea in winter during standard surveys. Larvae captured in November/December 2016 and January/February 2017 using the International Council for the Exploration of the Seas standard 2 m Midwater Ring trawls (MIK) were analysed to gain a better understanding of the pelagic early life-history stages of lemon sole, especially in relation to the timing of spawning and the dispersal of overwintering larvae. Larval age was estimated from sagittal otolith primary increment counts. The larvae caught in November/December ranged in nominal age from 4 to 45 days post-hatching which suggests that spawning continues into late October and November. Most, but not all, of the larvae caught in January/February were post metamorphosis, and the difference in age between the two sampling dates was consistent with the elapsed time between samplings. The estimated hatching dates confirm that lemon sole spawning extends into late autumn in the northern North Sea, with overwintering larvae in all developmental stages. Drift modelling of eggs and larvae released at historically documented spawning grounds in the northern North Sea suggests that these grounds are also the source for all of the larvae sampled during the 2016–2017 surveys.     

Comparison between the life cycles of two Soleidae, the common sole, Solea solea, and the thickback sole, Microchirus variegatus, in the Bay of Biscay (France)

The life history of two Soleidae, the common sole, Solea solea, and the thickback sole, Microchirus variegatus, were compared in the Bay of Biscay in an attempt to set out factors which could explain settlement styles known to be different between juveniles of each species. Common sole juveniles had been shown to depend on coastal and estuarine nurseries, and the thickback sole to develop in open-sea nurseries, although the spawning grounds and spawning season of both species overlapped (offshore and at springtime, respectively). For this study, data on adult, juvenile and larva distributions were obtained from cruises carried out in the Bay of Biscay during the last decade. In addition, growth rate of larvae and planktonic interval duration, estimated by means of otolith increment analysis, were compared, as well as literature-derived information on behaviour of larvae. By comparing larval features, it appeared that thickback sole did not obtain the advantage of a slightly longer pelagic life span for an increased dispersal, due to an early shift to benthic behaviour. Other evidence was given by more specifically stated distributions that the further and deeper offshore spawning of M. variegatus, compared to S. solea, was a likely key-factor of the juvenile settlement process. This could explain why the thickback sole, contrary to the common sole, never reach coastal areas and thus settle offshore, in waters deeper than 30 m.     

Vertical Distribution and Feeding Activity of Metamorphosing Sole, Solea Solea, Before Immigration to the Bay of Vilaine Nursery (Northern Bay of Biscay, France)

To evaluate the impact of metamorphosis on the vertical distribution and feeding activity of sole, Solea solea, larvae passing from offshore spawning grounds to the Bay of Vilaine, sampling series at fixed stations were carried out in April 1991 and April 1993 at depths from 50 to 30 m. Comparisons between plankton and bottom samplin series indicated differences in vertical distribution of larvae in pre-metamorphic and metamorphic steps. Metamorphosing larvae displayed a tendency to concentrate in the lower part of the water column, mainly during the day. Gut contents, analysed for prey identification, fullness index and carbon content, indicated that metamorphosing larvae fed mostly on plankton. Variations in fullness index were observed not only during the day, but also depended on tide and wind-induced mixing conditions. Larvae sampled in mixed spring-tide waters had highly variable carbon estimates, resulting in unclear diel activity. More larvae fed actively at neap-tide, which allowed the observation of a diurnal feeding activity through hourly changes in carbon estimates. It is concluded that immigrating sole were not yet able to settle but prepared themselves for demersal life (i) without undergoing starvation and (ii) by modifying the patterns of vertical distributions. The presence of a larval swimbladder suggests they can adjust their vertical movements, depending on tidal cycles, which could in turn favour coastal accumulation of metamorphosing larvae and pulses of new settlers entering the nursery grounds.     

Modelling population dynamics of the pelagic larval shrimp Metapenaeus ensis in the Osaka Bay estuary

Aiming at providing numerical tools useful to assess the impacts of coastal development pressures on marine life, a Lagrangian model for population dynamics of pelagic eggs and larvae of the greasyback shrimp, Metapenaeus ensis, in Osaka Bay was developed and improved based on laboratory experiments. The model was combined with a 3-D Eulerian numerical model that predicts physical and biological conditions of the habitat. A series of numerical experiments was done to investigate their transport processes from the spawning grounds, and the concentration process of full-grown larvae towards the mouth of Yodo River that flows into the innermost basin. Model results revealed, as a general tendency, that the early larval developmental stages through nauplius to zoea continue to drift like a passive tracer, and begin to concentrate at the river mouth area after the mysis stage, mainly avoiding low saline environment in the surface layer. This suggests that the full-grown larvae may be favored with chance to take advantage of the river-induced gravitational circulation that dominates the innermost estuarine basin. In addition, it was found that tidal condition around the spawning period also exerts a considerable influence upon the fate of pelagic larvae.     

Effect of spawning ground location on the transport and growth of chub mackerel (Scomber japonicus) eggs and larvae in the East China Sea

Chub mackerel (Scomber japonicus) are an important pelagic fish species within the China Sea. Annual recruitment of this species is determined primarily by survival in the early life history stages. Minor changes in the physical marine environment can have a significant effect on the growth and survival of eggs and larvae, thereby affecting recruitment of population. To model this interaction, we constructed a bio-physical dynamic model of the early life history of chub mackerel in the East China Sea (ECS). The physical model was based on the unstructured grid Finite Volume Coast and Ocean Model (FVCOM) and simulated the 3-D physical fields. The biological model was based on individual-based models (IBMs) in which the early life stages of chub mackerel were divided into five stages based on age or length. The model was parameterized using functions describing spawning, growth, and survival for chub mackerel in the ECS. Using this coupled physical and biological model, driven by the March–July climatological forcing, we tracked super individuals from spawning grounds to the nursery grounds to evaluate the influence of the physical environment at each of the spawning locations (western, normal, eastern) on the transport and survival of chub mackerel. The model suggests that spawning location has a significant effect on larval transport, although the larvae were generally advected northeastward to enter the Japan/East Sea through the Tsushima/East Strait or southeastward with the Kuroshio Current which then flows along the eastern Japanese coast. Spawning to the west was highly influenced by the Taiwan Warm Current (TWC) during early transport when the larvae were advected northward and then northeastward. The speed of drifting during this period was relatively slow. The model predicted that a large number of eggs and larvae would enter and transit through China’s coastal waters (Changjiang River Estuary, Hangzhou Bay, and the Zhoushan Islands). Under this scenario, the majority of larvae were transported to the northern nursery grounds, 79% to the nursery at Jeju Island and 10% to the nursery at Tsushima Strait. In contrast, only 11% were transported to the southern nursery grounds in the Pacific Ocean and Kyushu. Larvae spawned at the eastern spawning ground were primarily influenced by the Kuroshio Current which transported the larvae southeastward. Kuroshio acts as a barrier, restricting larvae from being advected to the interior of the western Pacific Ocean. Under such circumstances, almost no eggs and larvae were retained in the coastal waters of China. Instead, the larvae were rapidly transported northeastward from the Chinese shelf towards the coast of Japan. The model predicted that a large number of larvae would be transported to the southern nursery grounds in the Pacific Ocean and Kyushu, before entering the Pacific Ocean and Japan Sea. In total, 36% of larvae were transported to the Pacific Ocean nursery, 45% to the northern nursery grounds of Jeju Island and Tsushima Strait, and 27% to the Jeju Island nursery. The three simulations assumed the same number of eggs were spawned (2.17 × 10¹²) and the survival of larvae at the western, normal, and eastern spawning grounds was 0.0306%, 0.0353%, and 0.0234%, respectively. The average length was 123.7, 126.0, and 123.5 mm, respectively. Our results suggest that larvae spawned in different regions encountered different physical environments and were subject to different transport processes. These differences explain the changes in survival and growth observed between larvae from the different areas. Survival and growth was highest for chub mackerel that were spawned at the normal spawning location and subject to suitable water depths and temperatures during transport.     

The influence of spawning and nursery grounds on the distribution of sole Solea solea (L.) in the Irish Sea, Bristol Channel and adjacent areas

In the coastal waters of west England and Wales, sole, Solea solea (L.), are found in greatest abundance in the north-east Irish Sea and the Bristol Channel. Data from research and charter vessel surveys in these areas showed differences in the spatial distribution of age-groups between the two regions. Juvenile sole (0-group, 1-group and 2-group) were found almost exclusively in the shallow (<20 m deep) parts of the north-east Irish Sea and adults (3-group and older) were also found in the same area and in deeper water. In contrast, while juvenile sole in the Bristol Channel were abundant in and around Carmarthen Bay, Swansea Bay and the Severn estuary, they also occurred frequently in deeper areas of the Bristol Channel down to depths of 40 m. Adult sole in the Bristol Channel were also relatively more abundant at depths >40 m than adults in the Irish Sea. The movements of sole which produce these patterns of distribution in the two areas are also shown by the recaptures of sole tagged in the respective nursery areas. The differences in the distribution of sole in the two areas may be related to the depths of their spawning grounds and the distances that maturing fish must travel to reach them.

In the north-east Irish Sea, sole spawning grounds are generally in waters of <40 m depth and within an extensive area of relatively shallow and gently shelving sediments close to the coastal nursery grounds. The bottom topography of the Bristol Channel is more steeply shelving and the spawning grounds of sole are at a depth of 40–75 m off Trevose Head, ≈100 km from the main nursery areas. The hydrographic conditions in the two areas are described, and it is concluded that one of the more important requirements of a successful spawning ground is the presence of suitable hydrographic conditions to transport eggs and larvae to nursery areas.     

三峡库区丰都江段鱼类早期资源现状

2014 年47 月鱼类主要繁殖季节于三峡库区(重庆丰都县)进行鱼类早期资源调查, 以了解三峡库区鱼类早期资源现状, 四大家鱼在库区是否仍有产卵场等问题。调查共采集到鱼类50 种, 分属5 目9 科。采集时, 卵汛出现在6 月后流速较高的时段, 其中贝氏的数量最多, 占86.24%。仔鱼出现的高峰期为6 月上旬至7 月中旬, 太湖新银鱼的数量最多, 占58.36%, 其次为子陵吻虎鱼, 占27.04%。在仔鱼中, 种类组成呈明显的月份差异, 4 月鲤、鲫占数量优势;5 月太湖新银鱼、子陵吻 虎鱼占数量优势;6 月后鲌亚科、鳅科、鳜等种类开始出现, 种类明显增多。通过估算, 调查期间流经丰都断面的鱼卵总量为4.37108 粒, 四大家鱼鱼卵为0.21107 粒;仔鱼总量为111.98108 尾, 四大家鱼仔鱼为0.21108 尾。通过产卵场的推算, 丰都断面采集的四大家鱼来自涪陵城区江段和三峡库区上游的重庆巴南区至朱沱镇江段的产卵场。通过对卵苗漂流密度的昼夜规律分析, 6 月之前夜间仔鱼密度显著高于白天, 而6 月后仔鱼昼夜漂流密度无显著差异。本研究表明, 从三峡库尾进入三峡水库的鱼类早期资源丰富, 大部分鱼类繁殖发生在6 月以后水温较高、入库流量大、库区流速较高的时段, 库尾部分江段在流速较高时期, 仍存在四大家鱼的产卵场。       

基于个体的东海鲐鱼生长初期生态模型的构建

采用FVCOM物理模型生成三维物理场,基于个体模型参数化东海鲐鱼早期生物过程,通过拉格朗日质点的方法将模拟生成的3-7月物理场和生物模型进行耦合,构建了基于个体的东海鲐鱼早期生态模型.结果表明:所构建模型可很好地模拟东海鲐鱼鱼卵和仔鱼的输运过程和丰度分布,台湾暖流、黑潮和对马暖流直接影响鱼卵和仔鱼的输运和分布,通过输运到不同育肥场的温度和食物差异间接地影响鱼卵和仔鱼的生长、生存.东海南部产卵场对东海东北部渔场有很大的补充量,但对长江口和舟山外海渔场的补充量很少.产卵场的西北部、西南部与济州岛、对马海峡育肥场之间有很大的连通性,产卵场的东北部、东南部与九州岛、太平洋育肥场之间有很大的连通性.     

Dispersion of vendace eggs and larvae around potential nursery areas reveals their reproductive strategy

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Ontogenic migration of Pleuronectes flesus larvae in the eastern English Channel

Along the French coast of the eastern English Channel there is a strong separation in the hydrology, zooplankton community and ichthyoplankton assemblages, between a coastal ecosystem of continental influence and an offshore ecosystem of Atlantic influence. During April and May 1995, two surveys (60 stations) were conducted to describe the early life history of fishes in this area, and especially the influence of hydrodynamics on Pleuronectes flesus larval transfer from the spawning grounds to the nurseries. Ontogenic changes in larval distributions were described by variograms and path analysis. P. flesus eggs and young larvae were found in the southern offshore area. Their distributions were mainly influenced by sediment and cold temperature found in the central part of the Channel. Older larvae were found at more northern stations, showing a clumped distribution near estuaries, in areas of low salinity. Apparently, young stages of this species were transported from the south central spawning area to coastal waters by residual currents. Behavioural changes in older larvae facilitate the move to nurseries along the French coast.     

Genetic Analysis of the Populations of Japanese Anchovy (Engraulidae: Engraulis japonicus) Using Microsatellite DNA

We analyzed the population structure of the Japanese anchovy (Engraulis japonicus), a small pelagic fish, using 6 microsatellite DNA loci. The anchovy is known to have 2 separate spawning populations, one near northeastern Taiwan in the Pacific Ocean and the other near southwestern Taiwan in the Taiwan Strait. The planktonic larvae then drifted north to the feeding grounds in the East China Sea to advance in their life history. Three populations of the anchovy were analyzed, including 2 temporal population from the northeastern spawning ground (I-Lan 1999 and I-Lan 2000) and one population from the southwestern spawning ground (Peng-Hu 2000). The genetic variability of the 6 loci was high for all the populations. The average numbers of alleles per population ranged from 25.5 to 32.3, and the average observed heterozygosity ranged from 0.559 to 0.650. A significant population differentiation was found between geographic populations but not between the temporal populations. However, the level of geographic differentiation was weak, average FST 0.0088. The significant geographic population structure indicated that the populations of 2 spawning grounds belonged to separate stocks. Moreover, 16 of the 18 population-locus cases showed significant departure from Hardy-Weinberg equilibrium, implying that each spawning population in turn consisted of mixed native stocks. Finally, we posed 3 population models to be evaluated against the genetic data disclosed with the microsatellite markers.     

Diel patterns of larval drift of honmoroko Gnathopogon caerulescens in an inlet of Ibanaiko Lagoon,Lake Biwa,Japan

Diel drift patterns of larvae of the endangered cyprinid Gnathopogon caerelescens in an inlet of the Ibanaiko Lagoon, connected to Lake Biwa in Japan, were assessed in April 2012. Peak occurrence of yolk‐sac larvae was within a few hours after dark. Drift of newly hatched larvae is considered to be an important biological mechanism that ensures larval dispersal and recruitment from the inlets (spawning grounds) to the lagoon which functions as a nursery ground.     

Reproductive adaptations of Antarctic benthic invertebrates

The majority of Antarctic benthic invertebrates so far studied do not produce pelagic larvae, but develop non-pelagically by means of egg capsules, brooding or viviparity. The predominance of protected development in the Antarctic benthos is primarily due to the short period of summer phytoplankton abundance and the low sea temperature. Such conditions make it difficult for a larva to complete pelagic development before food becomes scarce in the surface waters. Prosobranch gastropods illustrate some important aspects of Antarctic benthic invertebrate reproduction. Species which develop non-pelagically have an aseasonal or prolonged spawning period. They produce a small number of large yolky eggs which remain in the benthos and develop slowly, giving rise to large, fully competent juveniles. Conversely, one species with free development has a short, synchronous spawning period during early summer, producing larvae which can benefit from the phytoplankton bloom. Protected development by means of brooding will limit dispersion, but transport on floating algae and by anchor ice may partially compensate for this in the Antarctic.     

Larval growth and drift pattern and the separation of herring spawning groups in the North Sea*

Data from two internationally co-ordinated survey programmes are used in an attempt to display the events in the early life that took place during the ‘recovery period’ of the North Sea herring Stock, 1979–1986. During the period, an increasing importance of the spawning grounds off Buchan and off Yorkshire is evident from distributions of newly hatched herring larvae. The dramatic changes in relative importance of spawning grounds are traced in the data on both late larvae (6 months old) and juveniles (18 months old). The onset of extended spawning off Buchan and off Yorkshire was followed by increase in distinct groups of late larvae of large mean length, and by enlargement of a group of medium-sized juveniles. It is hypothesized that the identified groups are interconnected. Thus, larvae spawned off Buchan and off Yorkshire are found to have growth rates superior to those attained by larvae from west of Scotland and around the Orkney/Shetland Isles, whereas the relationship is reversed in the juveniles. In the investigated period, larval drift routes exhibited the same trends from year to year, the drift of the northerly spawned larvae being the most variable. Thus, changes in the relative contributions from spawning grounds apparently influence the overall spatial distribution as well as size composition of larval and juvenile North Sea herring. The findings indicate that groups of larvae retain, to a large extent, separate distributions until metamorphosis, and point to larval drift pattern as a determinant of spawning group distinctness.     

Complex effect of projected sea temperature and wind change on flatfish dispersal

Climate change not only alters ocean physics and chemistry but also affects the biota. Larval dispersal patterns from spawning to nursery grounds and larval survival are driven by hydrodynamic processes and shaped by (a)biotic environmental factors. Therefore, it is important to understand the impacts of increased temperature rise and changes in wind speed and direction on larval drift and survival. We apply a particle‐tracking model coupled to a 3D‐hydrodynamic model of the English Channel and the North Sea to study the dispersal dynamics of the exploited flatfish (common) sole (Solea solea). We first assess model robustness and interannual variability in larval transport over the period 1995–2011. Then, using a subset of representative years (2003–2011), we investigate the impact of climate change on larval dispersal, connectivity patterns and recruitment at the nursery grounds. The impacts of five scenarios inspired by the 2040 projections of the Intergovernmental Panel on Climate Change are discussed and compared with interannual variability. The results suggest that 33% of the year‐to‐year recruitment variability is explained at a regional scale and that a 9‐year period is sufficient to capture interannual variability in dispersal dynamics. In the scenario involving a temperature increase, early spawning and a wind change, the model predicts that (i) dispersal distance (+70%) and pelagic larval duration (+22%) will increase in response to the reduced temperature (?9%) experienced by early hatched larvae, (ii) larval recruitment at the nursery grounds will increase in some areas (36%) and decrease in others (?58%) and (iii) connectivity will show contrasting changes between areas. At the regional scale, our model predicts considerable changes in larval recruitment (+9%) and connectivity (retention ?4% and seeding +37%) due to global change. All of these factors affect the distribution and productivity of sole and therefore the functioning of the demersal ecosystem and fisheries management.     

Hatch-period-dependent early growth and survival of Pacific herring Clupea pallasii in Miyako Bay, Japan

Considerable interannual variation in the abundance of larval and juvenile Pacific herring Clupea pallasii was detected in Miyako Bay, on the Pacific coast of northern Japan; abundances were high in 2001 and 2003 and low in 2000 and 2002. Hatch dates and growth rates for larval and juvenile survivors were estimated through otolith analysis. Water temperature and food availability were monitored on the spawning and nursery grounds in the inner part of the bay. The number of spawning females caught in nets set around the spawning ground was recorded during each spawning season (January to May) in 2000–2003. No correlation was found between the number of spawning females and the abundance of larvae and juveniles on the spawning and nursery grounds. The hatch dates of surviving larvae and juveniles were concentrated at the end of the spawning season in 2001 and in the middle of the season in 2003. The larvae experienced relatively high prey concentrations during the first-feeding period in 2001 but low concentrations in 2003. Survival of larvae during the first-feeding period may be a function of prey concentration as well as water temperature. In 2003, low water temperature would reduce starvation mortality during the first-feeding period. In contrast, unfavourable feeding conditions with higher temperatures during the first-feeding period seemed to result in low larval survival in 2000 and 2002. The 2001 larvae grew faster than those in 2003 because of the late hatch dates and the higher ambient temperatures that resulted. Temperature might be a major factor controlling growth rates of C. pallasii larvae in Miyako Bay.     

太湖五里湖仔稚鱼时空分布特征

为探究五里湖仔稚鱼群落结构及分布特征，于2016年4—10月对五里湖仔稚鱼进行系统调查。期间共采集仔稚鱼70678尾，共鉴定出鱼类20种(属)，隶属于7目8科18属。五里湖仔稚鱼密度均值为3825尾/100 m3，主要优势种为?属(Hemiculter sp.)，其数量占比为68.76%。五里湖仔稚鱼主要采集于4—8月，密度高峰期为6月，各物种密度高峰期存在差异，最早的为鲤(Cyprinus carpio)、鲫(Carassius auratus，4月)，最晚的为短吻银鱼属(Salangichthys sp.，8—9月)。五里湖仔稚鱼分布具有显著的空间差异，沿岸带仔稚鱼密度显著高于(P<0.05)敞水区，密度分别为5650和310尾/100 m3。西五里湖仔稚鱼的密度高于东五里湖，密度分别为4482和3600尾/100 m3。典范对应分析结果显示，水温、溶解氧、浮游植物和浮游动物密度是与仔稚鱼分布显著相关的环境因子(P<0.05)。研究结果显示，五里湖鱼类主要繁殖期为4—8月，主要产卵和育幼水域为沿岸带，其中西五里湖的育幼功能优于东五里湖，因此进一步维持对西五里湖的生境保护，加强东五里湖沿岸带植被恢复及入湖支流水质监控，控制外源污染物，对促进五里湖生境优化及鱼类资源自然增殖具有积极意义。     

The application of acoustic Doppler current profilers to measure the timing and patterns of coral larval dispersal

An experiment was conducted along the reefs off west Maui, Hawaii, during the summer of 2003 to monitor the spawning of the reef-building coral Montipora capitata and to determine the role of ocean currents in dispersing the larvae from the natal reef. Instruments documented the environmental forcing during the coral spawning season; drifters were deployed on three successive nights following direct observations of coral spawning. Both the timing and relative magnitude of the coral spawning were identifiable in acoustic backscatter data and correlated to plankton tow data. Each drifter track showed that the surface water containing coral eggs and planula larvae were transported rapidly offshore and not locally retained. Wind and current patterns during the previous year and during subsequent coral spawning events later in the summer were similar to those observed during the drifter releases. This suggests that the trajectories observed during the focused experiment are representative of the general pattern of larval dispersal off west Maui. These findings demonstrate the application of acoustic profilers for remotely imaging coral spawning and predicting their initial dispersal patterns.     

The abundance and patterns of the egg and larval spatial distribution of Eastern Baltic cod Gadus morhua callarias (Gadidae) in 1931–1996

According to ichthyoplankton surveys of AtlantNIRO and published sources, the data on abundance of eggs and larvae of eastern Baltic cod Gadus morhua callarias at different spawning grounds of the Baltic Sea in 1931–1938, 1949–1956, and 1991–1996 are considered. We show that a similar type of spatial distribution of eggs and larvae of cod with localization of the greatest amount of its early ontogenetic stages in the Bornholm Basin in the southwest of the sea was observed in the 1930s and 1990s. The extension of the area of distribution was accompanied by an increase in the numbers of eggs and larvae of cod in all areas of the sea, and its decline was followed by a decrease in numbers, in the first turn, at northeastern spawning grounds in the Gotland Basin. The period of high numbers of eggs in 1949–1956 coincided with the century maximum of salinity of the near-bottom water layer.     

An alternative mode of larval development inScoloplos armiger (O. F. Müller, 1776) (Polychaeta,Orbiniidae)

During a three-year plankton monitoring at the island of Helgoland (German Bight, North Sea), pelagic larvae ofScoloplos armiger (O. F. Müller, 1776) were observed to occur regularly from February to April. Up to the present day, only benthic development within egg cocoons has been described (Anderson, 1959). Planktonic larvae comprise early, ovoid trochophores up to advanced stages with 11 setigers. The main morphological difference between the two larval types is the more numerous differentiation of lateral cilia by the pelagic larvae. Annual alterations in appearance and abundance suggest that reproduction is correlated with water temperature.