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.     

Effect of habitat conditions on reproduction of the European anchovy (Engraulis encrasicolus) in the Strait of Sicily

The aims of this study were to describe the reproductive cycle of the European anchovy (Engraulis encrasicolus) off the south coast of Sicily and determine whether intra‐ and inter‐annual reproductive trait variations, if any, are adaptive responses which maximize reproductive success under environmental fluctuations. Biological data were collected from purse seine and mid‐water pelagic trawl commercial catches landed in Sciacca (Sicily) over 6 yr (1997–2002) at fortnightly intervals, analysing a total of 84 581 individuals. No inter‐annual changes in length at first reproduction were observed, with a mean pooled value of 11.26 cm for both sexes being found. Spawning intensity, indicated by gonadosomatic index, condition factor and length–weight relationships, seem to be governed by food availability prior to spawning. Anchovy reproductive investment was limited by the area's low primary production. There was a synchrony between reproductive cycle and temperature. Water warming marks the onset of a period of high water stability in the area, and its later cooling marks the onset of a period with low water stability. The relationship between reproductive cycle and temperature is therefore probably a reproductive strategy having evolved to ensure that spawning takes place during the period of the year when water column stability is higher, favouring food concentration and egg and larval retention in the spawning areas.     

From egg to juvenile in the Bay of Biscay: spatial patterns of anchovy (Engraulis encrasicolus) recruitment in a non‐upwelling region

In this study the spatial distribution of eggs, larvae and juveniles of European anchovy (Engraulis encrasicolus) was followed in 2004 and 2005 during three consecutive cruises each year in spring–summer to test what the limits of retention are in a non‐upwelling area. Eggs, small larvae and large juveniles were mainly distributed over the shelf, whereas large larvae and small juveniles were found mainly off the shelf. Although overall distributions were similar, the 2 yr differed in that there was more of a coastal distribution of individuals in 2004, whereas in 2005 more individuals were found off the shelf. There were no significant differences in the length–weight relationships for individuals found on and off the shelf or between years. The correspondence in circulation patterns and the lack of difference in the length–weight relationships suggest that a single population is present, larvae drifting off the shelf due to currents and returning as mobile juveniles. Quantile regression analysis of the long‐term recruitment index suggests that transport off the shelf may favour good recruitments. This would suggest that in non‐upwelling regions the retention area resulting in good recruitment may not be restricted to the shelf.     

Relationships between anchovy (Engraulis encrasicolus) recruitment and environment in the Bay of Biscay (1967–1996)

Various hypotheses have been put forward to explain the mechanisms leading to recruitment variability in fish populations. These have been based on either physical (wind stress, upwelling) or biological (food and predation) processes. In the Bay of Biscay, the hypothesis of a physical influence on anchovy recruitment has been confirmed. Oceanographic conditions in the Bay of Biscay in the spring and summer, influenced by north-easterly winds of medium and low intensity, seem to induce good levels of recruitment to the anchovy ( Engraulis encrasicolus ) population. An index of upwelling was significantly correlated with annual recruitment of anchovy ( P  < 0.0001) for the period 1967–1996. This physical parameter explains about 59% of the variability in the recruitment of the Bay of Biscay anchovy. Two factors affecting productivity in the Bay of Biscay may be linked to north-easterly winds, namely weak upwelling and an extension of the area influenced by river outflows. Both of these factors, together with low turbulence and stability, may act to enhance survival of the early life-history stages of anchovy by increasing food availability. The potential use of this upwelling index to forecast the recruitment of the Bay of Biscay anchovy offers possibilities for improving the management of this population.     

`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.     

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.     

Development and evaluation of a high‐throughput single nucleotide polymorphism multiplex assay for assigning pedigrees in common carp

Accurate pedigree information is critical when managing animal breeding programmes and ensure the highest rate of genetic gain. The abundance of available genomic data and the development of high‐throughput genotyping platforms have facilitated the use of single nucleotide polymorphisms (SNPs) as the best DNA markers for genomic selection studies. Furthermore, the superior qualities of SNPs compared with those of microsatellite markers allow standardization between laboratories, which is crucial for developing an international set of markers for use in traceability studies. The objective of this study was to develop a high‐throughput SNP array to assign common carp pedigrees accurately. A 48‐SNP array was developed based on the Fluidigm genotyping platform, and a phylogenetic analysis was performed to distinguish different pedigrees. A likelihood‐based approach was used to infer parental pairs, and the pair with the highest LOD score (log of the ratio of the likelihood given parentage to likelihood given non‐parentage) was assigned. The SNP genotypes of the offspring and candidate parents tested were collected, and 94% of the offspring were assigned to the most‐likely parent pair, which was consistent with the actual pedigree records. Using this SNP assay will allow implementation of offspring testing at large commercial farms where improved accuracy of pedigree assignments and genetic evaluations will increase genetic gains in the common carp aquaculture industry.     

Recent changes in the spawning grounds of Black Sea anchovy,Engraulis encrasicolus

Towards the end of the 1980s, when the spawning grounds in the northwestern shelf (NWS) of the Black Sea were lingering with the effects of eutrophication and of an exotic invasive ctenophore, a series of basin‐wide international ichthyoplankton surveys pointed out an increase in the anchovies spawning in the southern half of the Black Sea. Later, with the help of international conservation efforts, several key littoral ecosystem components within the anchovy's historical spawning grounds showed signs of recovery. However, the fate of the spawning stock anchovy in the south remained unanswered. In order to present the current situation in the southern Black Sea after two decades, an ichthyoplankton survey adopting the same methodology as previously used was undertaken during the peak spawning season of the Black Sea anchovy (BSa). The survey showed that the density of eggs was by far greater than for any of the surveys conducted previously. A wider geographical distribution of the eggs indicated an increase in the number of vagrants which had drifted away from the known spawning grounds. In contrast, the increased reproductive activity in the south signifies existence of a growing, non‐migrating southern BS stock. This stock seems to utilize the coastal hydrographic features associated with the rim current facilitating escape (loophole) from gelatinous predators such as Mnemiopsis leidyi and Aurelia aurata.     

Assessing the variability of hydrographic processes influencing the life cycle of the Sicilian Channel anchovy, Engraulis encrasicolus, by satellite imagery

Three oceanographic surveys carried out in the Sicilian Channel during the spawning season (June to July) of anchovy (Engraulis encrasicolus) showed a close relationship between anchovy reproductive strategy and important hydrographic structures. A time series of satellite‐derived sea surface temperature images of the Sicilian Channel were analysed by means of empirical orthogonal functions and the dominant empirical modes were studied in detail. The first empirical mode captured much of the original variance and reproduced the trajectory of the Atlantic Ionian Stream (AIS), the principal hydrodynamic feature of the area. The time coefficients of modes 1 and 2 had seasonal signals which, when combined, accounted for the enhancement of the thermal front, clearly visible off Cape Passero (southernmost coast of Sicily) during summer. As the area constituted the principal nursery ground of the Sicilian Channel anchovy, the combination of the time coefficients of these modes was considered a potential indicator of the food particle concentration usually associated with oceanic fronts, which provided the energy requirements for larval growth. Mode 3 described the north/south displacements of the mean AIS trajectory, which modified the surface temperature regime of the anchovy spawning habitat. Therefore, the time coefficients of this mode were used as a potential indicator of anchovy spawning habitat variability. The capability of time coefficients of modes 2 and 3 to modify the main pattern depicted by mode 1 were tested successfully against in situ oceanographic observations.     

Distribution and settling of Japanese anchovy (Engraulis japonicus eggs at the spawning ground off Changjiang River in the East China Sea

Spatial patterns in the distribution and abundance of Japanese anchovy, Engraulis japonicus, eggs were studied from net surveys in the East China Sea in May 1991. Egg abundance was> 5 × 10³ eggs (100 m³)^?1 in the area off Changjiang River, where a large spawning ground was developed. The vertical distribution of living eggs showed a maximum concentration at the surface (40700 eggs (100 m³)^?1) and rapidly decreased to ～5000 eggs (100 m³)^?1 at 14 m. Newly spawned eggs (stage I) were found throughout the water column but were most abundant near surface. Some eggs were morphologically identified as dead owing to their abnormal development and physical damage. In contrast to living eggs, no dead eggs were found at the surface and the concentrations were low to 21 m depth (40–64 eggs (100 m³)^?1). The concentration increased markedly with increasing depth, reaching a maximum of 634 eggs (100 m³)^?1 near the bottom (35 m). Dead eggs accounted for less than 0.3% of the total caught within 7 m of the surface and increased exponentially to 12% near the bottom. The settling loss of dead anchovy eggs also was studied by employing sediment traps at the spawning ground. The downward flux of settling eggs was low (304–405 eggs m^?2 day^?1) at 15 and 20 m depths, but rapidly increased with increasing depth, reaching a maximum of 1622 eggs m^?2 day^?1 at 35 m (5 m above bottom). By comparing the egg flux at 20 m with the living eggs abundance in the upper 20 m, the settling loss of eggs was calculated as about 0.098 day^?1. This probably represents the natural mortality of anchovy eggs caused by genetic abnormalities and incomplete fertilization.     

Modelling the effect of buoyancy on the transport of anchovy (Engraulis capensis) eggs from spawning to nursery grounds in the southern Benguela: an IBM approach

An individual‐based model (IBM) was used to investigate the effects of physical and biological variables on the transport via a jet current of anchovy (Engraulis capensis) eggs from spawning to the nursery grounds in the southern Benguela ecosystem. As transport of eggs and early larvae is considered to be one of the major factors impacting on anchovy recruitment success, this approach may be useful to understand further the recruitment variability in this economically and ecologically important species. By coupling the IBM to a 3D hydrodynamic model of the region called Plume, and by varying parameters such as the spatial and temporal location of spawning, particle buoyancy, and the depth range over which particles were released, we could assess the influences of these parameters on transport success. A sensitivity analysis using a General Linear Model identified the primary determinants of transport success in the various experimental simulations, and model outputs were examined and compared with patterns observed in field studies. Model outputs compared well with observed patterns of vertical and horizontal egg distribution. Particle buoyancy and area of particle release were the major single determinants of transport success, with an egg density of 1.025 g cm^?3 maximizing average particle transport success and the western Agulhas Bank being the most successful spawning area. This IBM may be useful as a generic prototype for other upwelling ecosystems.     

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.     

Predicting the vertical profiles of anchovy (Engraulis mordax) and sardine (Sardinops sagax) eggs in the California Current System

Several published models exist for simulating vertical profiles of pelagic fish eggs, but no one has rigorously assessed their capacity to explain observed variability. In this study, we applied a steady‐state model, with four different formulations for vertical diffusivity, to northern anchovy (Engraulis mordax) and Pacific sardine (Sardinops sagax) eggs in the California Current region. Vertical mixing profiles, based on wind speed and hydrography, were combined with estimated terminal ascent velocities of the eggs based on measurements of egg buoyancy and size, to simulate the vertical profiles of the eggs. We evaluated model performance with two data sets: (1) vertically stratified tows for both species and (2) paired samples for sardine eggs from 3‐m depth and in vertically integrated tows. We used two criteria: whether the model predicted individual observed vertical profiles (1) as well as the observed mean and (2) better than the observed mean. Model predictions made with the formulation producing the most gradual profile of vertical diffusivity provided the best match to observations from both data sets and for both species. Addition of a random error term to the terminal ascent velocity further improved prediction for anchovy eggs, but not sardine. For the paired data, model prediction of integrated abundance from abundance at 3‐m depth had significantly lower mean square error than prediction based on a linear regression of 3 m on integrated abundance. Our results support the feasibility of using data from the Continuous Underway Fish Egg Sampler quantitatively as well as qualitatively in stock assessments.     

A Bayesian model for anchovy (Engraulis encrasicolus): the combined forcing of man and environment

Fishery collapses frequently result from combined pressures of the environment and man, which are difficult to discern because of the complexities involved and our limited knowledge. Models to resolve this complexity often become too sophisticated, with too many assumptions and, consequently, with little capacity to predict beyond calibration data. In this paper we implement a different procedure where the model is kept simple and uncertainty accounts for the equation imperfectness to reproduce ecological complexity. Human and environmental forcing on an anchovy ( Engraulis encrasicolus ) stock are simulated with only six parameters plus their error terms, and the uncertainty is computed with Bayesian methods. The simple structure is able to reproduce the major dynamical features of this species in the Gulf of Cádiz, including data on life stages and age structure that had no contact with the model. This is a distinct performance for a frugal approach working on a mid-trophic species and a positive instance where parsimony can simulate the interaction of man, fish and the environment, provided uncertainty is accounted for in the process.     

Impact of freshwater input and wind on landings of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) in shelf waters surrounding the Ebre (Ebro) River delta (north-western Mediterranean)

Time series analyses (Box–Jenkins models) were used to study the influence of river runoff and wind mixing index on the productivity of the two most abundant species of small pelagic fish exploited in waters surrounding the Ebre (Ebro) River continental shelf (north‐western Mediterranean): anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus). River flow and wind were selected because they are known to enhance fertilization and local planktonic production, thus being crucial for the survival of fish larvae. Time series of the two environmental variables and landings of the two species were analysed to extract the trend and seasonality. All series displayed important seasonal and interannual fluctuations. In the long term, landings of anchovy declined while those of sardine increased. At the seasonal scale, landings of anchovy peaked during spring/summer while those of sardine peaked during spring and autumn. Seasonality in landings of anchovy was stronger than in sardine. Concerning the environmental series, monthly average Ebre runoff showed a progressive decline from 1960 until the late 1980s, and the wind mixing index was highest during 1994–96. Within the annual cycle, the minimum river flow occurs from July to October and the wind mixing peaks in winter (December–April, excluding January). The results of the analyses showed a significant correlation between monthly landings of anchovy and freshwater input of the Ebre River during the spawning season of this species (April–August), with a time lag of 12 months. In contrast, monthly landings of sardine were significantly positively correlated with the wind mixing index during the spawning season of this species (November–March), with a lag of 18 months. The results provide evidence of the influence of riverine inputs and wind mixing on the productivity of small pelagic fish in the north‐western Mediterranean. The time lags obtained in the relationships stress the importance of river runoff and wind mixing for the early stages of anchovy and sardine, respectively, and their impact on recruitment.     

Biophysical modelling of larval drift, growth and survival for the prediction of anchovy (Engraulis encrasicolus) recruitment in the Bay of Biscay (NE Atlantic)

Fish recruitment is the result of the integration of small‐scale processes affecting larval survival over a season and large oceanic areas. A hydrodynamic model was used to explore and model these physical–biological interaction mechanisms and then to perform the integration from individual to population scales in order to provide recruitment predictions for fisheries management. This method was applied to the case of anchovy (Engraulis encrasicolus) in the Bay of Biscay (NE Atlantic). The main data available to investigate survival mechanisms were past growth (otolith) records of larvae and juveniles sampled at sea. The drift history of these individuals was reconstructed by a backtracking procedure using hydrodynamic simulations. The relationships between (real) growth variation and variations in physical parameters (estimated by hydrodynamic simulations) were explored along the individual trajectories obtained. These relationships were then used to build and adjust individual‐based growth and survival models. Thousands of virtual buoys were released in the hydrodynamic model in order to reproduce the space–time spawning dynamics. Along the buoy trajectories (representative of sub‐cohorts), the biophysical model was run to simulate growth and survival as a function of the environment encountered. The survival rate after 3 months of drift was estimated for each sub‐cohort. The sum of all these survival rates over the season constituted an annual recruitment index. This index was validated over a series of recruitment estimations. The modelling choices, model results and the potential use of the recruitment index for fisheries management are discussed.     

Historical fluctuations in spawning location of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) in the Bay of Biscay during 1967–73 and 2000–2004

The spatial extent of small pelagic fish spawning habitat is influenced by environmental factors and by the state of the adult population. In return, the configuration of spawning habitat affects recruitment and therefore the future structure of the adult population. Interannual changes in spatial patterns of spawning reflect variations in adult population structures and their environment. The present study describes the historical changes in the spatial distribution of spawning of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) in the Bay of Biscay during two periods: 1967–72 and 2000–2004. Using data from egg surveys conducted in spring, the spatial distributions of anchovy and sardine eggs are characterized by means of geostatistics. For each survey, a map of probability of egg presence is constructed. The maps are then compared to define (1) recurrent spawning areas, (2) occasional spawning areas and (3) unfavourable spawning areas during each period. Sardine spawning habitat is generally fragmented and appears spatially limited by the presence of cold bottom water. It is confined to coastal or shelf break refuge areas in years of restricted spawning extent. For anchovy, recurrent spawning sites are found in Gironde and Adour estuaries whilst spawning can extend further offshore in years of more intense spawning. For both species, the mean pattern of spawning has changed between 1967–72 and 2000–2004. Noticeably, the spatial distribution of anchovy eggs in spring has expanded northward. This trend possibly results from changes in environmental conditions during the last four decades.     

Predicting the current and future suitable habitat distributions of the anchovy (Engraulis ringens) using the Maxent model in the coastal areas off central‐northern Chile

An assessment of climate change impacts on the habitat suitability of fish species is an important tool to improve the understanding and decision‐making needed to reduce potential climate change effects based on the observed relationships of biological responses and environmental conditions. In this study, we use historical (2010–2015) environmental sea surface temperature (SST), upwelling index (UI), chlorophyll‐a (Chl‐a) and biological (i.e., anchovy adults acoustic presence) data (i.e., Maxent) to determine anchovy habitat suitability in the coastal areas off central‐northern (25°S–32°S) Chile. Using geographic information systems (GIS), the model was forced by changes in regionalized SST, UI and Chl‐a as projected by IPCC models under the RPC (i.e., RCP2.6, RCP4.5, RCP6.0 and RCP8.5) emissions scenarios for the simulation period 2015–2050. The model simulates, for all RCP scenarios, negative responses in anchovy presence, reflecting the predicted changes in environmental variables, dominated by a future positive (warming) change in SST and UI, and a decrease in chlorophyll‐a (i.e., phytoplankton biomass). The model predicts negative changes in habitat suitability in coastal areas from north of Taltal (25°S) to south of Caldera (27°45′S) and in Coquimbo littoral zone (29°–30°12′S). The habitat suitability models and climate change predictions identified in this study may provide a scientific basis for the development of management measures for anchovy fisheries in the coastal areas of the South American coast and other parts of the world.