Sardine Eggs Research Articles

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

AbstractWinter 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.

Effects of formalin preservation on egg size of small pelagic fish as major target species in ichthyoplankton surveys

AbstractPreservation is critical for egg and larval samples from ichthyoplankton surveys. As growing interest is directed toward maternal effects on egg quality, historical collections of egg samples in formalin are potentially invaluable materials but concerns about the effects of formalin preservation need to be clarified. The present study examined effects of formalin preservation on egg size of Japanese sardine Sardinops melanostictus, chub mackerel Scomber japonicus and Japanese anchovy Engraulis japonicus over a long period (30–36 months). Overall, the egg sizes slightly decreased in a couple of months after preservation but then recovered to be at a similar level to the live eggs for diameters of spherical eggs of sardine and mackerel and short diameters of ellipsoidal eggs of anchovy, although a caveat lies in unstable and slightly increasing patterns in long diameters of anchovy eggs. No substantial differences were found between 5% and 10% formalin solutions. For practical purposes, we conclude that no correction factors are required for using the measurements of egg samples preserved in formalin over a long period. Assuming the applicability to congeneric species, the information presented here supports the validity of previous studies and will promote future studies on egg size variability in small pelagic fish based on historical collections of egg samples preserved in formalin in various regions of the world.

Modelling the spatial distribution of Sardina pilchardus and Engraulis encrasicolus spawning habitat in the NW Mediterranean Sea

We investigated the main drivers of eggs and larvae distributions of European sardine and anchovy from the NW Mediterranean Sea. We used Generalized Additive Models and satellite environmental data. Mainly sea surface temperature, but also currents, surface height, and primary production were significantly correlated with both species’ early stages distributions. Anchovy optimal temperature upper limit was not detected, but sardine eggs and larvae presented a small-ranged bell-shape curve relationship to SST with an upper SST threshold around 13 °C. Sardine spawning during winter appeared to be dependant not only on in-situ environmental conditions but also on summer conditions prior to the spawning event. Model predictions of the larval and spawning habitat distribution showed clear differences between developmental stages and between species, confirming a worsening of the sardine habitat with time. Considering the further increase of surface temperature predicted in the years to come, the survival of the sardine in the region could be compromised.

Food-web dynamics in the Portuguese continental shelf ecosystem between 1986 and 2017: Unravelling drivers of sardine decline

The Ecopath food web model that describes the Portuguese continental shelf ecosystem was fitted to available time series to investigate the ecosystem dynamics and decline of the Portuguese sardine stock. Our results showed that the Portuguese continental shelf ecosystem model is a good predictor of biomass and catch time-series trends for many species. Moreover, our results suggested that the main factors that drove the ecosystem dynamics were trophic interactions, fishing and environmental forcing (sea surface temperature). The same drivers were important in explaining sardine decline among which the largest contribution was observed when incorporating sea surface temperature forcing on adult sardine, followed by fishing. Moreover, sardine eggs predators (i.e., chub mackerel, horse mackerel and bogue) were emphasised as the most important among trophic interactions in explaining sardine trend between 1986 and 2017. Furthermore, a flow control hypothesis test, showed that model parametrization allows explaining sardine behaviour through wasp-waist control mechanism, characteristic for upwelling systems. This study represents an important step forward in understanding the changes that occurred in the Portuguese continental shelf ecosystem and provides helpful insights to explain Portuguese sardine decline.

Long term variation of sardine Sardina pilchardus spawning along the Atlantic coast of northwest Africa (21–26°N): characterization and spatiotemporal variability in spawning habitat

Small pelagic fish such as sardine show strong recruitment variability often associated with environmental changes influencing the spawning process and ultimately, affecting population dynamics. Sardine (Sardina pilchardus, Walbaum 1792) is one of the most exploited pelagic species along the northwest African coast. The main spawning occurs during the cold season (autumn–winter). A time-series autumn–winter surveys extending from 1994 to 2015 sampled sardine eggs, along the southern area of the Moroccan Atlantic coast (26°N–21°N) were analyzed. The present work focuses on examining the inter-annual variability of the spawning habitat by analyzing the spatial-temporal variability of sardine egg distribution and density extracted from the data collected over the period 1994–2015. Generalized additive models (GAM) were used to detect the relationships between the sardine distribution, expressed as egg density and the presence or absence data and relevant hydrobiological environmental variables, such as salinity, temperature and zooplankton biomass. The generalized additive models showed significant relationships between the environment variables (SST, SSS and Zooplankton biomass) and sardine density, but not with sardine presence. Given that the study area is characterized by high mesoscale features and significant upwelling activities, the variability of upwelling processes could explain the changes of spawning ground position and thermal window.

The Abundance and Distribution of the Early Life Stages of Sardine (Sardina pilchardus) in Central of the Aegean Sea (Sığacık Bay) and their Interactions with Certain Environmental Factors

The study was carried out on a monthly basis at 16 stations between January 2017 and December 2017 in the Sigacik Bay, Izmir, Turkey. For ichthyoplankton sample collections, vertical (350 μm) plankton tows were carried out using a WP-2-type plankton net with a mouth area of 0.255 m2. Depth, temperature, oxygen, pH, salinity, zooplankton volume and chlorophyll-a values were detected at each research station in the study. The eggs and larvae of the sardine samples were obtained during the period between December and February, the maximum being in February (mean temperature 15.29 ± 0.57 °C). The mean abundance values of all sardine eggs and larvae in all stations were 78 individuals·10 m−2. The egg diameter values in sardines were in the range of 1.40–1.69 mm and the oil globule diameter values were in the range of 0.12–0.18 mm. The majority of sardine eggs and larvae were found at the depths of 25–75-m at the stations. The correlation between the abundance of sardine eggs and larvae and environmental variables was determined using the Principal Component Analysis (PCA). There was a positive correlation between sardine eggs and dissolved oxygen (r: 0.75) and a negative correlation between larvae and salinity (r:-0.75). It was concluded that sardine does not prefer Sigacik Bay as a spawning area. However, further ichthyoplanktonic studies considering the fluctuations of pilchard stocks in Sigacik Bay should be carried out for a longer period to better clarify the issue.

Investigating connectivity between two sardine stocks off South Africa using a high‐resolution IBM: Retention and transport success of sardine eggs

AbstractThis study applied a previously used Lagrangian individual‐based model (IBM) for sardine in the Southern Benguela to an improved and more robust hydrodynamic model to investigate whether a more representative spatial coverage, greater horizontal and vertical resolution, more realistic winds and improved representation of mesoscale features such as eddies and filaments would give different results for transport and retention of early life stages. Despite major differences between the old and new hydrodynamic models, overall the IBM results were quite similar to the previous southern Benguela sardine IBM study. This surprising result indicates that it is the macroscale circulation features resolved by the two hydrodynamic models that are controlling transport and retention of sardine early life stages. The contribution of transient mesoscale features such as eddies and filaments appears to be less important when transport patterns are averaged over the 21‐year‐long experiment. Another aim of this study was to better estimate the contribution of south coast spawning to west coast sardine recruitment. This was possible because of an eastward extension of the geographical domain of the new hydrodynamic model which provided a more realistic representation of the south coast spawning ground. Three main spawning and nursery area systems, similar to those identified in the previous sardine IBM, were identified: west coast and west coast (WC‐WC), south coast and west coast (SC‐WC), and south coast and south coast (SC‐SC). Spawning area proved to be an important determinant of modelled retention and transport success, with spawning depth also playing an important role on the west coast. The main difference observed from the previous study was an increase in the average percentage of particles released on the south coast and transported to the west coast (P0, 17.4%). This indicates more connectivity between the southern and western sardine stocks than previously thought and is therefore important for fishery management. Standardized anomalies from the modelled retention/transport were compared with recruitment estimates from stock assessment models but there was no correlation between the two sets of anomalies. However, a significant correlation was observed between the modelled retention/transport anomalies for the west coast and total cumulative upwelling anomalies for the Southern Benguela (r = −0.67, p < .001).

Analysing Temporal Variability in Spatial Distributions Using Min–Max Autocorrelation Factors: Sardine Eggs in the Bay of Biscay

This paper presents a novel application of the geostatistical multivariate method known as min–max autocorrelation factors (MAFs) for analysing fisheries survey data in a space–time context. The method was used to map essential fish habitats and evaluate the variability in time of their occupancy. Research surveys at sea on marine fish stocks have been undertaken for several decades now. The data are time series of yearly maps of fish density, making it possible to analyse the space–time variability in fish spatial distributions. Space–time models are key to addressing conservation issues requiring the characterization of variability in habitat maps over time. Here, the variability in fisheries survey data series is decomposed in space and time to address these issues, using MAFs. MAFs were originally developed for noise removal in hyperspectral multivariate data and are obtained using a specific double principal components analysis. Here, MAFs were used to extract the most continuous spatial components that are consistent in time, together with the time series of their amplitudes. MAFs formed an empirical isofactorial model of the data, which served for kriging in each year using all available information across the data series. The approach was applied on the spawning distributions of sardine in the Bay of Biscay from 2000 to 2017. A multivariate approach for dealing with space–time data was adapted here, because the evolution in time was highly variable. Maps were classified using the amplitudes of the MAFs, and groups of typical distributions were identified, which showed different occurrence probabilities in different periods.

Variación a largo término (2002-2016) en la densidad y composición del mesozooplancton indica cambio de régimen en isla Margarita (Venezuela)

In the east of Margarita Island (Venezuela), the composition and density of mesozooplankton were studied for 15 years (2002 to 2016) in two fixed stations five miles from the coast. Samples (total 655) collected biweekly by hauls using net with a diameter of 1.7 m and a length of 3.5 m (mesh size of 400 microns) towed horizontally at a depth of 10 to 15 m for 20 minutes. The abundance of the main planktonic groups (21) was estimated by their density (ind/m3) by direct counting. In 13 groups: copepods, cladocerans, sergestoids Lucifer, brachyurans zoea, chaetognaths, mollusk larvae, cirripede larvae, penaeid mysis, pteropods and in the gelatinous plankton (salps,appendicularians, jellyfish, siphonophores) during the periods 2002-2004 and 2014-2016, lower values of annual density and representation were found, while in 2005-2013 the values were notoriously higher. The sardine eggs deviate from the indicated trend, since they were more abundant in years 2002-2004 and 2014-2016 and were lower in density between 2005 and 2013. This trend was more notable in its representation (%) in mesozooplankton. Due to the greater abundance of 13 zooplankton groups and their total density, it is confirmed that a regime shift occurred affecting ecosystem services such as sardine fishing, generating an approximately 10-year long crisis.

Physical-biological interactions in the ocean: case studies from the northern Canary Current Upwelling Ecosystem

Physical-biological interactions in the ocean: case studies from the northern Canary Current Upwelling Ecosystem

A GIS-based framework for addressing conflicting objectives in the context of an ecosystem approach to fisheries management—a case study of the Portuguese sardine fishery

Abstract An ecosystem approach to fisheries management (EAFM) is as a new paradigm in fisheries management. In this study, a combination of geographic information systems (GISs) and multi-criteria decision-making method (MCDM) is proposed as a framework supporting an ecosystem approach to European sardine (Sardina pilchardus, Clupeidae) fishery management in Portugal. This case study was chosen due to the recent severe decline shown by the species. To develop an EAFM for the sardine fishery, a set of criteria were defined based on literature review and expert knowledge. To address multiple conflicting objectives, namely conservation and fisheries, five scenarios were considered: (i) baseline; (ii) nurseries protection; (iii) spawning areas protection; (iv) fishery profit driven, and (v) safeguarding dependent fishing communities. Combination of GIS and MCDM methods highlighted important areas to implement spatial conservation measures for sardine. The analyses indicate that some areas are suitable for conservation in several scenarios, such as the area near Aveiro and the area near the Tejo estuary. However, conservation measures implemented in the area near Aveiro would imply higher economic trade-offs when compared with the actions applied in the region near the Tejo estuary. Results also suggested some of the conservation objectives, such as the protection of sardine eggs and juveniles, to not be compatible. The proposed framework is an important tool supporting EAFM by addressing conflicting objectives, trade-offs and identifying areas that could be considered as potential fishery closure sites or subjected to further analyses.

The impact of kraft pulping effluent on egg survival and hatching success in two species of Clupeiformes (Teleostei).

The anchoveta (Engraulis ringens) and sardine (Strangomera bentincki) are coastal pelagic species with important spawning areas off the coast of Chile. The discharge of secondary-treated effluents from a kraft pulp plant near one of these spawning areas has raised environmental concerns. Therefore, effluent effects on the development of anchoveta and sardine eggs were assessed by in vitro exposure. Eggs were sampled between 2007 and 2010 off Talcahuano, Chile. Subsequent toxicity tests (96h duration, 12°C) were performed using increasing effluent concentrations, a filtered seawater control, and two potassium dichromate concentrations (to verify consistent embryonic sensitivity). Egg mortality and hatching success were evaluated. For anchoveta, mortality (9.9 ± 7.1%) did not significantly differ among groups in five toxicity tests except the final toxicity test that showed significant differences in mortality (5.6% control vs 27.8% in 100% effluent). For sardines, no differences in mortality existed between the effluent dilutions (2.6 ± 3.6%) and control (6.3 ± 3.9%). Notably, anchoveta egg survival and hatching success rates were inconsistent, i.e., the highest rates of hatching failure occurred on the same sampling date with the highest rates of survival for the 100% effluent group (72%). In conclusion, the obtained results indicate that (i) anchoveta egg mortality and hatching failure increase only under 100% effluent exposure, coinciding with decreased egg quality near the end of spawning season and (ii) high effluent dilutions not significantly increase sardine and anchoveta egg mortalities. Nevertheless, the recorded adverse effects to the hatching process should be studied in greater detail, particularly considering interspecific variability and the complexity of reproductive processes, especially during early development.

Sardine (Sardina pilchardus) larval dispersal in the Iberian upwelling system, using coupled biophysical techniques

The European sardine (Sardina pilchardus) is the most important small pelagic fishery of the Western Iberia Upwelling Ecosystem (WIUE). Recently, recruitment of this species has declined due to changing environmental conditions. Furthermore, controversies exist regarding its population structure with barriers thought to exist between the Atlantic-Iberian Peninsula, Northern Africa, and the Mediterranean. Few studies have investigated the transport and dispersal of sardine eggs and larvae off Iberia and the subsequent impact on larval recruitment variability. Here, we examine these issues using a Regional Ocean Modeling System climatology (1989–2008) coupled to the Lagrangian transport model, Ichthyop. Using biological parameters from the literature, we conduct simulations that investigate the effects of spawning patchiness, diel vertical migration behaviors, and egg buoyancy on the transport and recruitment of virtual sardine ichthyoplankton on the continental shelf. We find that release area, release depth, and month of release all significantly affect recruitment. Patchiness has no effect and diel vertical migration causes slightly lower recruitment. Egg buoyancy effects are significant and act similarly to depth of release. As with other studies, we find that recruitment peaks vary by latitude, explained here by the seasonal variability of offshore transport. We find weak, continuous alongshore transport between release areas, though a large proportion of simulated ichthyoplankton transport north to the Cantabrian coast (up to 27%). We also show low level transport into Morocco (up to 1%) and the Mediterranean (up to 8%). The high proportion of local retention and low but consistent alongshore transport supports the idea of a series of metapopulations along this coast.

The ZooCAM, a new in-flow imaging system for fast onboard counting, sizing and classification of fish eggs and metazooplankton

In this paper we present the ZooCAM, a system designed to digitize and analyse on board large volume samples of preserved and living metazooplankton (i.e. multicellular zooplankton) and fish eggs >300 µm ESD. The ZooCAM has been specifically designed to overcome the difficulties to analyse zooplankton and fish eggs in the framework of the PELGAS survey, and provide high frequency data. The ZooCAM fish eggs counts were comparable to those done with a dissecting microscope. The ZooCAM enabled the accurate prediction and fast on board validation of staged anchovy and sardine eggs in almost real time after collection. A comparison with the ZooScan, on a more complex zooplanktonic community, provided encouraging results on the agreement between the 2 instruments. ZooCAM and ZooScan enabled the identification of similar communities and produced similar total zooplankton abundances, size distributions, and size spectra slopes, when tested on the same samples. However these results need to be further refined due to the small number of samples used to compare the two instruments. The main ZooCAM drawback resides in a slight but sensible underestimation of abundances and sizes, and therefore individual and community biovolumes. The ZooCAM have been successfully deployed over 4 years, on numerous surveys without suffering any major failure. When used in line with the CUFES it provided high resolution maps of staged fish eggs and zooplanktonic functional groups. Hence the ZooCAM is an appropriate tool for the development of on board, high frequency, high spatial coverage zooplanktonic and ecosystemic studies.

A real-time PCR approach to detect predation on anchovy and sardine early life stages

Recruitment of sardine (Sardina pilchardus Walbaum, 1792) and anchovy (Engraulis encrasicolus Linnaeus, 1758) is thought to be regulated by predation of their eggs and larvae. Predators of sardine and anchovy can be identified by visual taxonomic identification of stomach contents, but this method is time consuming, tedious and may underestimate predation, especially in small predators such as fish larvae. Alternatively, genetic tools may offer a more cost-effective and accurate alternative. Here, we have developed a multiplex real-time polymerase chain reaction (RT-PCR) assay based on TaqMan probes to simultaneously detect sardine and anchovy remains in gut contents of potential predators. The assay combines previously described and newly generated species-specific primers and probes for anchovy and sardine detection respectively, and allows the detection of 0,001ng of target DNA (which corresponds to about one hundredth of the total DNA present in a single egg). We applied the method to candidate anchovy and sardine egg predators in the Bay of Biscay, Atlantic Mackerel (Scomber scombrus) larvae. Egg predation observed was limited primarily to those stations where sardine and/or anchovy eggs were present. Our developed assay offers a suitable tool to understand the effects of predation on the survival of anchovy and sardine early life stages.

ECOLOGÍA COSTERA AL SURESTE DE ISLA MARGARITA, VENEZUELA (ABRIL 2012 – MAYO 2014)

Venezuela, until 2005 Southeast of Margarita Island was an important area in sardine fishing Sardinella aurita but catches declined sharply even until 2013; therefore, pelagic environmental conditions were studied and compared with those obtained in years when there were abundant sardine catches. For 26 months (April/2012 to May/2014) in three fixed stations sampling (every two weeks for 14 months and monthly 12 months) at depths of 1 and 20 m, horizontal hauls (10-15 m depth) for 20 minutes were made in order to study hydrography, nutrients, primary production, chlorophylls, and abundance of mesozooplankton. In 2012 and 2013 it was verified that the local aquatic fertility remained low compared to 2003-2004. In 2014 some fertility recovery was denoted by increased nutrients (nitrite and nitrate); chlorophylls a and b notably increased to 3.79 and 1.81 mg/m3 respectively and primary production to 497.97 mgC/m3/day. The average density of zooplankton ranged between 131.21 and 192.49 ind/m3, thesediment volumes 0.13-0.14 mL/m3 and dry weights between 0.62 and 0.95 mg/m3; the density of sardine eggs varied between 2.12 and 8.57/m3 and their representation in the plankton ranged between 1.88 and 6.24%, these values are much lower compared to those found in years with heavy sardine catches (2002- 2004).

Size, permeability and buoyancy of anchovy (Engraulis Encrasicolus) and sardine (Sardina Pilchardus) eggs in relation to their physical environment in the Bay of Biscay

AbstractThe size and specific gravity of eggs of marine pelagic fish partly determine their dispersal and survival. Using an original dataset of anchovy and sardine eggs, sampled in spring over the last decade in the Bay of Biscay, we provide a parameterization of these properties on ambient water temperature and salinity. We used the density gradient column for measurement of egg specific gravity. The column was also filled with homogeneous water for sinking velocity experiments. For anchovy, these experiments confirm that the effect of egg permeability through the chorion could be neglected when modelling sinking, while it has to be considered for sardine, its perivitelline space representing 78.6% (±6.2%) of the total egg volume, as opposed to 5–10% for most teleosts species. We estimated a coefficient of permeability of the chorion of 0.0038 mm s−1. However, permeability should not affect the measurement of sardine egg specific gravity in a gradient column, provided a minimum duration before reading is respected for equilibrium to be reached. In relation to their environment, we found that the egg specific gravity is largely determined by sea surface salinity for both species, whereas egg size is weakly but significantly impacted by temperature, for sardine only. On average, the estimated difference in specific gravity between egg and surface water is −0.92 σT for anchovy and −1.06 σT for sardine. The detailed parameterization of the relationship between eggs and water properties should prove useful, in particular to modellers dealing with the dispersal of fish early life stages.

DENSIDAD DE HUEVOS DE SARDINA SARDINELLA AURITA, ABUNDANCIA DE ZOOPLANCTON E HIDROGRAFÍA EN LA PENÍNSULA DE ARAYA Y SUR DE ISLA MARGARITA, VENEZUELA

During 18 months (October 2007 - March 2009) the density of eggs and larvae of round sardine Sardinella aurita, the abundance of mesozooplankton and hydrography were studied in three stations located south of Margarita island (Coche, Cubagua and Macanao) and three stations at the Araya Peninsula (Guaca, Chacopata and Araya). Nocturnal horizontal hauls (20 minutes; 15-20 m depth) of plankton (net diameter 1.0 m; net length 2.5 m and mesh size 400 μm) and water samples (surface and 25 m) were collected to determinate temperature, salinity and dissolved oxygen. Eggs of sardine were found during all study months; in the Araya Peninsula the mean density ranged between 2.51 and 5.19 eggs/ m3 and ranged between 5.22 y 7.06 eggs/m3 at the south of Margarita Island. The highest density (47.51 eggs/m3) was found at Coche. The abundance of sardine eggs was minor than between 2002 and 2004 at the east of Margarita. The monthly mean density of total zooplankton ranged between 170.63 and 1032.8 ind/m3; the dry weight between 2.53 and 7.32 mg/m3 and the settled volume ranged between 0.26 and 0.38 mL/m3. The highest abundances of zooplankton and sardine eggs were found at Coche and Cubagua stations. The hydrography is discussed; the temperature values at the surface and at 25 m depth (means 26.5 and 24.9 °C) are considerate high and comparable to mean temperatures of previous years (2005 to 2007) and possibly affecting sardine abundance in the region.

Is the Russell Cycle a true cycle? Multidecadal zooplankton and climate trends in the western English Channel

The Russell Cycle is one of the classical examples of climate influence on biological oceanography, represented as shifts in the marine plankton over several decades with warm and cool conditions. While the time-series data associated with the phenomenon indicate cyclical patterns, the question remains whether or not the Russell Cycle should be considered a “true cycle”. Zooplankton time-series data from 1924 to 2011 from the western English Channel were analysed with principal component (PC), correlation and spectral analyses to determine the dominant trends, and cyclic frequencies of the Russell Cycle indicators in relation to long-term hydroclimatic indices. PC1 accounted for 37.4% of the variability in the zooplankton data with the main contributions from non-clupeid fish larvae, southwestern zooplankton, and overall zooplankton biovolume. For PC2 (14.6% of data variance), the dominant groups were northern fish larvae, non-sardine eggs, and southern fish larvae. Sardine eggs were the major contributors to PC3 (representing 12.1% of data variance). No significant correlations were observed between the above three components and climate indices: Atlantic Multidecadal Oscillation, North Atlantic Oscillation, and local seawater temperature. Significant 44- and 29-year frequencies were observed for PC3, but the physical mechanisms driving the cycles are unclear. Harmonic analysis did not reveal any significant frequencies in the physical variables or in PCs 1 and 2. To a large extent, this is due to the dominant cycles in all datasets generally being long term (>50 years or so) and not readily resolved in the examined time frame of 88 years, hence restricting the ability to draw firm conclusions on the multidecadal relationship between zooplankton community dynamics in the western English Channel and environmental indices. Thus, the zooplankton time-series often associated and represented as the Russell Cycle cannot be concluded as being truly cyclical.

Transport patterns of Pacific sardine Sardinops sagax eggs and larvae in the California Current System

We simulated transport of Pacific sardine eggs captured offshore of California in spring of 2001–2012 using a regional ocean circulation model. Eggs were assumed to have developed into larvae within a few days and were modeled using five behavioral patterns: passive transport, diel vertical migration, diel vertical migration combined with swimming against the current, diel migration combined with migration toward shore, and diel migration combined with migration toward the best habitat. Simulated larvae with no swimming behavior were advected far offshore to poor habitat where they were unlikely to survive. Diel vertical migration resulted in less offshore transport because larvae were less affected by surface currents during the day. However, in half the years simulated nearly all juveniles were also located in poor habitat by late summer in this scenario. Swimming against the current combined with diel vertical migration resulted in similar transport patterns to the diel-vertical-migration scenario because currents dominated the transport of eggs and small larvae during the spring and early summer. Migration toward shore resulted in a large fraction of juveniles being located in appropriate habitat during late summer in all years. Migration toward the best habitat was the best strategy modeled. This strategy resulted in a slightly greater proportion of larvae being located in appropriate habitat at the end of summer than the swimming-toward-shore scenario, despite the fact that most larvae were located farther offshore. These results suggest that larval sardine might use directed horizontal swimming behavior to remain in suitable habitat conditions. A large fraction of larvae were transported south into Mexican waters by late summer in all five scenarios. Surveying juvenile sardines in fall near the border of the U.S. and Mexico may be an efficient means of estimating recruitment because the advection pattern of eggs and larvae to the south is opposite the adult migration pattern to the north. This pattern may cause juveniles to be spatially segregated from adults at the time they are being recruited.