Relative importance of gulf and shelf waters for spawning and recruitment of Australian anchovy, Engraulis australis, in South Australia

Gonosomatic indices and egg and larval densities observed from 1986 to 2001 suggest that the peak spawning season of the Australian anchovy (Engraulis australis) in South Australia occurs during January to March (summer and autumn). This coincides with the spawning season of sardine (Sardinops sagax) and the period when productivity in shelf waters is enhanced by upwelling. Anchovy eggs were abundant throughout gulf and shelf waters, but the highest densities occurred in the northern parts of Spencer Gulf and Gulf St Vincent where sea surface temperatures (SST) were 24–26°C. In contrast, larvae >10 mm total length (TL) were found mainly in shelf waters near upwelling zones where SSTs were relatively low (<20°C) and levels of chlorophyll a (chl a) relatively high. Larvae >15 mm TL were collected only from shelf waters near upwelling zones. The high levels of larval abundance in the upwelling zones may reflect higher levels of recruitment to later stages in these areas compared with the gulfs. The sardine spawns mainly in shelf waters; few eggs and no larvae were collected from the northern gulfs. The abundance of anchovy eggs and larvae in shelf waters increased when sardine abundance was reduced by large‐scale mortality events, and decreased as the sardine numbers subsequently recovered. We hypothesize that the upwelling zones provide optimal conditions for the survival of larval anchovy in South Australia, but that anchovy can only utilize these zones effectively when the sardine population is low. At other times, northern gulf waters of South Australia may provide a refuge for the anchovy that the sardine cannot utilize.     

`Ocean triads' in the Mediterranean Sea: physical mechanisms potentially structuring reproductive habitat suitability (with example application to European anchovy, Engraulis encrasicolus)

Summaries of maritime weather reports and mean seasonal satellite-sensed ocean colour distributions for the Mediterranean Sea are used to identify characteristic configurations of physical mechanisms promoting (i) nutrient enrichment, (ii) concentration of larval food distributions, and (iii) local retention of eggs and larvae. Five subbasin scale `ocean triads', hypothesized to be particularly favourable groupings, are identified in the Aegean Sea, the Gulf of Lions and nearby Catalan Coast, the Alboran Sea, the Straits of Sicily/Tunisian Coast, and the Adriatic Sea. These are examined in relation to available knowledge of anchovy spawning grounds. All areas are characterized by patterns of linked wind-driven Ekman upwelling and downwelling. All areas except the Straits of Sicily are found to have inputs of less saline surface waters offering raised nutrient concentrations, enhanced upper layer stability, and frontal density contrasts, and to have areas where the characteristic rate of turbulent mixing energy input by the wind fall below a reference intensity level. All areas, except the Sicilian Channel/Tunisian Coast, also contain abundant locally reproducing anchovy populations.     

Entrainment and advection of larval sardine,Sardinops sagax,by the East Australian Current and retention in the western Tasman Front

The poleward flowing East Australian Current (EAC) drives sporadic upwelling, entrains coastal water and forms the western Tasman Front (wTF), creating a mosaic of water types and larval transport routes along south eastern Australia. The spatial distribution, otolith chemistry and growth rates of larval sardine (Sardinops sagax) were examined to infer spawning location and larval transport. A gradient of increasing larval size from north to south along the shelf was not detected but was evident between the shelf and offshore in the wTF. Here larvae were larger and older. Based on the occurrence of newly hatched larvae, spawning by S. sagax between southern Queensland and mid New South Wales (NSW) was more extensive than previously reported. The otolith chemistry from two wTF larval size classes differed, implying different origins. The otolith chemistry of wTF post‐flexion larvae was similar to larvae from northern NSW, whereas wTF flexion larvae were similar to larvae observed nearby from mid‐NSW. Two possible larval transport routes, direct and indirect, are inferred from otolith chemistry, current velocities and a previously published particle tracking study. Either larvae from northern NSW were advected south and entrained with younger larvae directly into the wTF, or larvae from a range of shelf regions were advected around the southern edge of an anticyclonic eddy, to join younger larvae directly entrained into the wTF. Based on the co‐occurrence of larval ages and sizes in the wTF and their advection routes, the wTF appears to be an important larval retention zone.     

Growth and movement patterns of early juvenile European anchovy (Engraulis encrasicolus L.) in the Bay of Biscay based on otolith microstructure and chemistry

Various hypotheses have been put forward to explain the mechanisms in the Bay of Biscay that result in a good recruitment of European anchovy. Anchovy larvae from the spawning area in the Gironde River plume are advected towards off-shelf waters, where juveniles are commonly observed. Otolith microstructural and chemical analysis were combined to assess the importance of this off-shelf transport and to determine the relative contribution of these areas for anchovy survival. Chemical analysis of otoliths showed that anchovy juveniles in the Bay of Biscay can be divided into two groups: a group that drifts towards off-shelf waters early in their life and returns later, and a group that remains in the low salinity waters of the coastal area. The first group presents significantly faster growth rates (0.88 mm day⁻¹) than those remaining in the coastal waters (0.32 mm day⁻¹). This may be due to off-shelf waters being warmer in spring/summer, and to the fact that the lower food concentration is compensated for by higher prey visibility. Furthermore, the group of juveniles that drifted off the spawning area and had faster growth rates represents 99% of the juvenile population. These findings support the hypothesis that anchovy in the Bay of Biscay may use off-shelf waters as a spatio-temporal loophole, suggesting that transport off the shelf may be favourable for recruitment.     

Hydrographic phenomena influencing early life stages of the Sicilian Channel anchovy

The information collected from a European Union funded project on the ‘Distribution Biology and Biomass Estimates of the Sicilian Channel Anchovy (Engraulis encrasicolus)’ was used to analyse the linkage between the general circulation pattern of the Atlantic Ionian Stream (AIS) and the reproductive strategy of the Sicilian Channel anchovy. The main spawning ground is located in the NW region of the southern Sicilian coast. This region is a stable area of low current produced by the impingement towards the coast of the AIS and its bifurcation into two branches. The main branch heads towards the SE end of the Sicilian coast (Cape Passero) acting as a transport mechanism for the anchovy eggs and larvae. Along the AIS trajectory, there is a density front to the left of the current, facing downstream. This front is a consequence of the shoreward sloping of isopycnals that maintains the geostrophic flow, facilitating the mixing of deeper waters with surface layers and fertilization of coastal waters. The front enhances primary production assuring food availability for anchovy larvae during their advection by the AIS. The highest concentrations of larval anchovy were found off the SE Sicilian coast, in the area off Cape Passero. The greater average sizes of larvae found in this region, and their estimated age, support the evidence of advection by the AIS. The hydrographic features observed in this area, such as the existence of a well‐defined cyclonic vortex, implies the existence of upwelling in its centre, providing a suitable environment for sustained enhanced rates of primary production and allowing the larval population to maintain their relative position. This retention area is conceived as favourable for providing the necessary feeding conditions. The data acquired from a survey carried out to evaluate the anchovy recruitment strength confirm that larvae reach the juvenile stage in the south‐eastern coast of Sicily, since most of the young‐of‐the‐year anchovy were located in the Cape Passero region.     

Nursery areas of Micromesistius poutassou and Sardina pilchardus unveil their reproductive strategies in the northwestern Mediterranean Sea

Winter conditions in the NW Mediterranean cause instability of the water column and non-geostrophic dynamics, such as vertical mixing and convection are significant. These events involve nutrient supply to the photic zone that can sustain high productivity. In this study, we aim to investigate the role of winter hydrodynamics on the spawning strategies of Sardina pilchardus and Micromesistius poutassou. Data were obtained on two oceanographic cruises (February 2017 and 2018) off the Catalan coast. The occurrence of S. pilchardus eggs very close to the coast indicated a clear preference of the species for spawning in coastal areas. Preflexion and postflexion larvae exhibited a slightly wider distribution showing a clear association with the cold, less saline and more productive coastal waters. Preflexion larvae of M. poutassou were found on the upper slope and over the shelf, being offshore limited by the shelf/slope front present all along the slope. The front would act as a barrier preventing their dispersion towards the open sea. M. poutassou larvae in advanced developmental stages were located close to the coast in the productive shelf waters, with instabilities of the front contributing to larval transport from offshore waters to the coast. The vertical distribution of both species showed high variability, not only related with the daily cycle or developmental stage, but also with the vertical structure of the water column. Overall, the results provide some clues on how the spawning strategies of both species may evolve under future scenarios of higher winter-stratification, because of the global warming.     

Distribution and abundance of South-west Atlantic anchovy spawners (Engraulis anchoita) in relation to oceanographic processes in the southern Brazilian shelf

The reproductive environment of the South-west Atlantic anchovy, Engraulis anchoita , in the southern Brazilian coast was investigated using maritime weather reports from the US National Climatic Center. These reports were summarized to yield seasonal distributions of sea surface temperature, wind stress and Ekman transport for 2-month segments of the seasonal cycle. The vertical oceanographic structure and dynamics were studied using temperature and salinity data collected from oceanographic cruises. The seasonal distribution and biomass of South-west Atlantic anchovy spawners were estimated by acoustic surveys. Anchoita spawns intensively off southern Brazil during winter and early spring when the Ekman transport is directed onshore, and the combined effects of freshwater run-off and the flow of cold water near the bottom result in a strong vertical stability over the continental shelf. During this season, primary production peaks due to nutrient input from Sub-Antarctic waters and freshwater run-off. These conditions would avoid dispersal of eggs and larvae offshore and favour the production and maintenance of fine-scale food particle aggregations required for successful first feeding of newly hatched larvae. In summer, the conditions are almost reversed and anchoita spawners are virtually absent from the area. Thus, the spawning strategy of anchoita in southern Brazil seems to be tuned in a way to optimize larval retention, minimize exposure to turbulent mixing and take advantage of enhanced plankton productivity.     

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.     

Simulation of the impact of climate change on the egg and larval transport of Japanese anchovy (Engraulis japonicus) off Kyushu Island,the western coast of Japan

In order to investigate the impact of climate change on egg and larval transport of Japanese anchovy (Engraulis japonicus) off Kyushu Island western Japan, we conducted particle‐tracking simulations on transport success/failure to fishing grounds from 1960 to 2007. The modeled transport success since the mid‐1990s increased and decreased in the offshore and coastal zones, respectively, compared with the 1960s and 1970s. The estimated northward shift of the spawning ground and weakened Tsushima Warm Current contributed to increase in modeled transport success to the offshore zone. Conversely, the weakening trend of the modeled onshore current in the Goto‐Nada Sea combined with the northward shift of the spawning ground resulted in unsuccessful larval transport. These results suggest that fluctuations in juvenile and subadult anchovy catches in this area may be attributable to changes in the physical environment. The present study showed that changes in transport success induced by oceanographic fluctuations related to climate change, have the potential to affect anchovy recruitment off the western coast of Japan.     

Transport of larval jack mackerel (Trachurus japonicus) estimated from trajectories of satellite-tracked drifters and advective velocity fields obtained from sequential satellite thermal images in the eastern East China Sea

Transport processes of jack mackerel (Trachurus japonicus) larvae in the waters off the west coast of Kyushu in the eastern East China Sea, have been investigated using satellite‐tracked surface drifters and consecutive satellite thermal images. Trajectories of drifters describe northward flows over the continental shelf, eastward flows of the Kuroshio south‐west of Kyushu, and a weak clockwise gyre off the west coast of Kyushu. In particular, the clockwise gyre causes the entrainment of jack mackerel larvae into the waters off the west coast of Kyushu. Consecutive satellite thermal images help to elucidate the northward warm water intrusion from the Kuroshio front south‐west of Kyushu. Particle trajectories using sea surface current fields computed with the Maximum Cross Correlation (MCC) technique also reveal that the transport of jack mackerel larvae into the nursery ground off the west coast of Kyushu caused by the anti‐cyclonic gyre and the warm streamers are an important process for successful recruitment.     

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.     

Processes controlling retention of spring‐spawned Atlantic cod (Gadus morhua) in the western Gulf of Maine and their relationship to an index of recruitment success

Atlantic cod, Gadus morhua, harvested in US waters are currently managed as a Gulf of Maine stock and as a stock comprising Georges Bank and southern New England populations. Over the past two and a half decades, success of age‐1 recruitment to the Gulf of Maine stock has varied by more than an order of magnitude. To investigate the hypothesis that this variation is related to variation in the transport of larval cod to nursery areas, we carried out model simulations of the movement of planktonic eggs and larvae spawned within the western Gulf of Maine during spring spawning events of 1995–2005. Results indicate that the retention of spring‐spawned cod, and their transport to areas suitable for early stage juvenile development, is strongly dependent on local wind conditions. Larval cod retention is favored during times of downwelling‐favorable winds and is least likely during times of upwelling‐favorable winds, during which buoyant eggs and early stage larvae tend to be advected offshore to the Western Maine Coastal Current and subsequently carried out of the Gulf of Maine. Model results also indicate that diel vertical migration of later stage larvae enhances the likelihood of retention within the western Gulf of Maine. Consistent with model results is a strong correlation between age‐1 recruitment success to the Gulf of Maine cod stock and the mean northward wind velocity measured in Massachusetts Bay during May. Based on these findings, we propose a wind index for strong recruitment success of age‐1 cod to the Gulf of Maine stock.     

Modelling the advection and diffusion of eggs and larvae of Greenland halibut (Reinhardtius hippoglossoides) in the north-east Arctic

Since the late 1980s there has been considerable uncertainty in recruitment levels of the north‐east Arctic stock of Greenland halibut (Reinhardtius hippoglossoides). The abundance of several year classes, originally considered very low at 0–3 yr age, appeared higher than expected at the age of 6+. This may be due to poor targeting of recruitment surveys of the younger year classes. The present work considers the transport and dispersion of eggs and larvae of Greenland halibut by numerical modelling in order to predict the locations of the initial recruitment grounds. Current fields from a 3D baroclinic hydrodynamic model are fed into a Lagrangian particle‐tracking model developed for the Barents Sea area. The particles are released into the current at the spawning field along the shelf slope from Lofoten to Bear Island (69–75°N). Vertically, the particles can follow a predefined depth‐by‐age curve or be kept at a fixed depth. This model system is used for different years to examine changes in the drift pattern. The results indicate that spawning location, transport depth and inflowing activity to the Barents Sea are important factors influencing the distribution of juveniles.     

Importance of the Shatsky Rise Area in the Kuroshio Extension as an offshore nursery ground for Japanese anchovy (Engraulis japonicus) and sardine (Sardinops melanostictus)

Recent findings suggest that recruitment of Japanese anchovy (Engraulis japonicus) and sardine (Sardinops melanostictus) depends on survival during not only the first feeding larval stage in the Japanese coastal waters and the Kuroshio front but also during the post‐larval and juvenile stages in the Kuroshio Extension. Spatial distributions of juvenile anchovy and sardine around the Shatsky Rise area in the Kuroshio Extension region and the Kuroshio–Oyashio transition region are described, based on a field survey in the late spring using a newly developed mid‐water trawl for sampling juveniles. All stages of anchovy from post‐larvae to juveniles were obtained in the northern Shatsky Rise area. The Kuroshio Extension bifurcates west of the Shatsky Rise area and eddies are generated, leading to higher chlorophyll concentrations than in the surrounding regions in April and May. When Japanese anchovy and sardine spawn near the Kuroshio front or the coastal waters south‐east of Japan, their larvae are transported by the Kuroshio Extension and are retained in the Shatsky Rise area, which forms an important offshore nursery ground, especially during periods of high stock abundance.     

Dispersal of Eastern King Prawn larvae in a western boundary current: New insights from particle tracking

Patterns in larval transport of coastal species have important implications for species connectivity, conservation, and fisheries, especially in the vicinity of a strengthening boundary current. An Ocean General Circulation Model for the Earth Simulator particle tracking model was used to assess the potential dispersal of Eastern King Prawn (EKP) larvae Melicertus (Penaeus) plebejus, an important commercial and recreational species in Eastern Australia. Particles were exposed to a constant natural mortality rate, and temperature‐dependent growth (degree‐days) was used to determine the time of settlement. Forward and backward simulations were used to identify the extent of larval dispersal from key source locations, and to determine the putative spawning regions for four settlement sites. The mean dispersal distance for larvae was extensive (~750–1,000 km before settlement), yet the northern spawning locations were unlikely to contribute larvae to the most southern extent of the EKP range. There was generally great offshore dispersal of larvae, with only 2%–5% of larvae on the continental shelf at the time of settlement. Our particle tracking results were combined with existing site‐specific reproductive potentials to identify the relative contributions of larvae from key source locations. Although mid‐latitude sites had only moderate reproductive potential, they delivered the most particles to the southern coast and are probably the most important sources of larval EKP for the two southern estuaries. Our modelling suggests that mesoscale oceanography is a strong determinant of recruitment success of the EKP, and highlights the importance of both larval dispersal and reproductive potential for understanding connectivity across a species’ range.     

Distribution of larval fishes among water masses in Onslow Bay, North Carolina: implications for cross-shelf exchange

The Gulf Stream (GS) is a major oceanographic feature with potential to influence the recruitment of larval fishes to continental shelf habitats in the southeastern United States. To test the hypothesis that the GS is a source of certain larval fishes to Onslow Bay, North Carolina, we (i) classified water masses as shelf, GS, GS front (GSF), or GS/shelf mixture (GS/S); (ii) compared larval fish assemblages and concentrations among these water masses; and (iii) compared length–frequency distributions and length–concentration relationships of indicator and commercially important taxa among water masses. A total of 21,222 larvae were collected with bongo and neuston nets from April 2000 to December 2001. Non-metric multidimensional scaling analyses revealed distinct larval assemblages associated with different water masses. For bongo catches, bothids were abundant in all water masses, gobiids, callionymids, and labrids were abundant in shelf waters, and myctophids and scombrids were abundant in the GS. For neuston catches, carangids dominated in GS/S, GSF, and GS waters, whereas triglids were abundant in shelf water. Larval concentrations in neuston catches were lower in shelf waters and higher in GS and GSF waters. Concentrations of most taxa in bongo catches were low in the GS and higher in shelf waters. We used trends in myctophid (offshore/GS) and gobiid (shelf) length–concentration data as indicators of the sources of commercially important serranids. Length distributions and concentrations of larval indicator taxa suggested local, shelf spawning, and transport of larvae from offshore.     

Alternating dominance of postlarval sardine and anchovy caught by coastal fishery in relation to the Kuroshio meander in the Enshu-nada Sea

In the mid 1970s, the fishery catch of postlarval Japanese anchovy (Engraulis japonica) in a shelf region of the Enshu‐nada Sea, off the central Pacific coast of Japan, started to decline corresponding to a rapid increase of postlarval sardine (Sardinops melanostictus). In late 1980s, sardine started to decline, and it was replaced by anchovy in the 1990s. This alternating dominance of postlarval sardine and anchovy corresponded to the alternation in egg abundance of these two species in the spawning habitat of this sea. It was also noteworthy that during the period of sardine decline, sardine spawning occurred in April–May, a delay of two months compared with spawning in the late 1970s. The implication of oceanographic changes in the spawning habitat for the alternating dominance of sardine and anchovy eggs was explored using time‐series data obtained in 1975–1998, focusing on the effect of the Kuroshio meander. Large meanders of the Kuroshio may have enhanced the onshore intrusion of the warm water into the shelf region and contributed to an increase in temperature in the spawning habitat. This might favour sardine, because its egg abundance in the shelf region was more dependent on the temperature in early spring than was that of anchovy. In addition, enhanced onshore intrusion could contribute to transport of sardine larvae from upstream spawning grounds of the Kuroshio region. On the other hand, anchovy egg abundance was more closely related to lower transparency at the shelf edge, which may indicate the prevalence and prolonged residence of the coastal water, and therefore higher food availability, frequently accompanying non‐meandering Kuroshio. The expansion/shrinkage of the spawning habitat of sardine and anchovy in the shelf region, apparently responding to the change in the Kuroshio, possibly makes the alternation in dominance of postlarval sardine and anchovy most prominent in the Enshu‐nada Sea, in combination with changes in the abundance of spawning adults, which occurred almost simultaneously in the overall Kuroshio region. The implication of this rather regional feature for the alternating dominance of sardine and anchovy populations on a larger spatial scale is also discussed.     

Larval lobster (Homarus americanus) distribution and drift in the vicinity of the Gulf of Maine offshore banks and their probable origins

Surveys for lobster larvae in offshore waters of the north‐eastern Gulf of Maine in 1983, 1987 and 1989 confirm that local hatching occurs mainly at depths <100 m over the banks, including Georges and Browns Banks. Detailed studies in the vicinity of Georges Bank in late July of both 1987 and 1989 indicate that the first and second moult stages were located primarily over the bank whereas stages III and IV lobster were collected both over and off the bank. At times stage IV lobster were more abundant off the bank than over it. The condition of stage III and IV lobster, as measured by a lipid index, was better off than over Georges Bank in 1988 and 1989 indicating a possible physiological advantage to being off the bank. In addition, the higher surface temperatures off Georges Bank would shorten larval development time to settlement. To determine the probable hatch sites of stage IV lobster collected off of Browns Bank in 1983 and off of Georges in 1987 and 1989, a 3‐D circulation model of the Gulf of Maine was used to simulate larval lobster drift backwards in time. In all cases, areas off Cape Cod, MA, and off Penobscot Bay, ME were suggested as the source of the larvae, although most of the larval trajectories never reached these near‐shore waters that are well‐known, larval hatching areas. The model‐projected larval release times match most closely the observed inshore hatch off Massachusetts but model uncertainties mean that coastal Maine cannot be ruled out as a source. Georges Bank is also a potential source because the present model does not take into account short‐term wind events, off‐bank eddy transport or the possibility of directed off‐bank larval swimming. Examination of weather records prior to and during our 1988 and 1989 sampling periods indicates that winds were not of sufficient intensity and duration to induce larval transport off Georges Bank. The shedding of eddies from the northern flank of Georges Bank into the Gulf of Maine are a relatively common phenomenon during summer but not enough is known about them to evaluate their contribution to possible cross‐bank transport of lobster larvae. Directed larval swimming is another possible source for the stage IV lobster found near Georges Bank. Plankton distributions across the northern frontal zone of Georges Bank in 1988 were used as proxies for the scarce larval lobsters. The more surface distribution of the microplankton, in particular, supports the possibility that wind and eddy events may be important in the transport of stage III and IV lobsters off of Georges Bank. Further studies are needed to evaluate these possible additional sources of advanced stage lobster larvae found off of the offshore banks.     

Larval Japanese eel (Anguilla japonica) as sub‐surface current bio‐tracers on the East Asia continental shelf

Larval Japanese eel (leptocephali) are passively transported from their spawning sites of the North Equatorial Current to the Kuroshio and its branch waters for 4–6 months before reaching the East Asian coasts. The larvae mainly stay within water depths between 50–150 m. The dispersal dynamics of larvae thus should reflect the sub‐surface oceanic currents on the East Asia continental shelf. An analysis of Japanese glass eel catch data in East Asian countries during 1985 to 2009, and for Taiwan from 1968 to 2008, indicates that the overall annual catch is generally correlated across countries of East Asia, and between north and west areas of Taiwan. The Kuroshio and its branch waters disperse glass eels throughout East Asian habitats, and the glass eel distribution matches the flow directionality of oceanic currents. Recruitment in western Taiwan occurs with a sequential southwestern to northwestern direction, suggesting that the Taiwan Strait Current penetrates the western coast of Taiwan in the sub‐surface layer in winter. The monthly averaged sub‐surface 50 m circulation pattern in the vicinity of Taiwan and modeled tracer experiments also support the northward winter sub‐surface current in Taiwan Strait. These results suggest that the larval Japanese eel could serve as a valuable bio‐tracer of sub‐surface currents, and the earlier recruitment dynamics of Japanese glass eels in Taiwan could be a good predictor for the subsequent catch in other East Asia areas.     

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.