Marine litter impacts oceans and affects marine organisms, representing a potential threat for natural stocks of pelagic fish species located at the first levels of the marine food webs. In ...2013–2014, on a seasonal basis, marine litter and microplastics in stomach contents from
Sardinia pilchardus
and
Engraulis encrasicolus
were evaluated. Selected species are plankitivores of great ecological and commercial importance in the Adriatic Sea. Collected data were correlated to possible factors able to affect ingested levels as well as species, season of sampling, biometry and sex of animals. Almost all tested samples (80 organisms for each species) contained marine litter (over 90% of samples from both species) and also microplastics; while any meso- or macroplastics were recorded. On average, recorded items were as follows: 4.63 (
S. plichardus
) and 1.25 (
E. encrasicolus
) per individual. Sardines evidenced a higher number of microplastics characterised by a smaller size than those recorded in anchovies
.
For sardines, sex, Gastro Somatic Index and sampling season showed negligible effects on the number of ingested litter; conversely, anchovies showed differences related with both sex of animals and dominant colour of ingested materials with prevalence for black and blue colours.
This study documented the levels of microplastics in three commercially important small pelagic fish species in South African waters, namely European anchovy (Engraulis encrasicolus), West Coast ...round herring (Etrumeus whiteheadi) and South African sardine (Sardinops sagax). Data suggested variation between species with a higher concentration of microplastics for S. sagax (mean of 1.58 items individual-1) compared to Et. whiteheadi (1.38 items individual-1) and En. encrasicolus (1.13 items individual-1). The occurrence of microplastics was also higher for S. sagax (72%) and Et. whiteheadi (72%) compared to En. encrasicolus (57%). Microfibres accounted for 80% of ingested microplastics (the remainder were plastic fragments) with the main ingested polymers being poly(ethylene:propylene:diene) (33% occurrence), polyethylene (20%), polyamide (20%), polyester (20%) and polypropylene (7%). The abundance of ingested items was not significantly correlated with fish caudal length or body weight, and spatial investigation indicated an increase in the abundance of ingested items from the West to the South coast. Etrumeus whiteheadi is proposed as a bio-indicator for microplastics for South Africa.
•A new calibration of a DEB model for anchovy and a first set of parameter estimates for sardine in the Bay of Biscay.•Using a robust method for parameter estimation, the evolution strategy, ...guaranteeing the uniqueness of the solution.•The sardine model is derived from the anchovy one through a scenario approach that successively tested the effect of distinctive traits (size, spawning, feeding).•Bioenergetics and reproduction strategy strongly interact.•Sardine displays a slower but more regular energy allocation to both growth and reproduction than anchovy.
Similar or very contrasted puzzling population dynamics between anchovy and sardine occur worldwide. Underlying factors are not well understood, but insights towards different biological traits are suggested, in particular trophic specialisation, leading to different responses to environmental conditions. Based on most striking differences in biological and life history traits, i.e. size, spawning and feeding, we calibrated a bioenergetics model, based on the Dynamic Energy Budget theory, for Engraulis encrasicolus and Sardina pilchardus in the Bay of Biscay. Starting from the anchovy model, differences in traits were successively integrated to build the sardine model through a novel exploratory approach by scenarios. We used a robust method for parameter estimation, the Evolution Strategies, with a large dataset of length and mass at age, as well as energy density, which is the first time in such a model calibration. Energy density data proved to be particularly well suited to assess the quality of DEB model predictions and parameter set estimates. Insights in respective physiology were drawn from analysis of parameter values and predictions of the model. We showed that anchovy and sardine have distinct strategies with respect to energy acquisition and especially to allocation to spawning. Anchovy are characterised by higher metabolic rates and requirements. This species is more likely to benefit from periods of high food availability to carry out both growth, spawning and reserve storage. Sardine have less demanding food requirements and metabolic costs. Sardine take advantage of larger reserves storage capacity to decouple spawning and prey blooms and to lengthen spawning period, and thus display a more capital breeding spawning behaviour. Overall, our model outputs distinguish between anchovy that tend towards an almost “all or nothing” energetic strategy, and sardine that tend to carry out lower metabolic activities but on a more regular basis. This first modelling demonstration of a bioenergetics difference between these two species, and the explanation it brings in the understanding of their respective reproduction strategies, opens new perspectives in the interpretation of their differential responses at the population scale to environment variability.
Abstract
This study measures the dorsal aspect target strength (TS; dB re 1 m2) and TS–length (standard length, SL; cm) relationships for European anchovy, attained both ex situ and in situ in two ...different seasons across 7 years in the Bay of Biscay. The measurements were made at three frequently used acoustic frequencies (38, 120, and 200 kHz). A backscattering model for physostome fish was utilized to help interpret the results. The obtained experimental mean TS for anchovies with an SL of 3.5–19.5 cm was −44.6 (±2.3), −46.9 (±3), and −48.4 (±2.7) dB at 38, 120, and 200 kHz, respectively, yielding b20 values of −66.4, −68.7, and −70.4 dB, respectively. The results were consistent across seasons and between in situ and ex situ conditions, presenting TS–length relationships with statistically significant slopes (p-values <0.05) for all frequencies. This research represents part of a series of efforts planned to obtain a comprehensive TS vs. length and depth relationship to update the acoustic assessment methodology of European anchovy in the Bay of Biscay.
In the NW Mediterranean Sea, anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) are the most important small pelagic fish in terms of biomass and commercial interest. Round sardinella ...(Sardinella aurita) and Sprat (Sprattus sprattus) are also present in this region. This paper provides a general insight into the ecology of these species through a revision of the information available in an environmental context and in relation to exploitation features. Spawning habitats of the two main species, anchovy and sardine, are clearly differentiated based on water mass characteristics reducing the overlapping between their early developmental stages. Larval distribution is also related to major productivity mechanisms of the respective spawning seasons. In spite of the different environmental regimes in which larvae of these species develop, growth rates are fairly similar. Trophic modeling highlights the important ecological role of small pelagic fish in North Western Mediterranean ecosystems. This review points out the gaps in knowledge necessary to understand the dynamics of small pelagic fish in the region and to progress towards a precautionary and adaptive management.
The European anchovy (Engraulis encrasicolus) being a species very rich in long‐chain fatty acids, it is subject to rapid spoilage with consequent sensory losses. Therefore, this study aimed to ...verify the effect of a low‐voltage electrostatic field (DENBA+) on the quality of fresh anchovies in a refrigerated environment. During 9 days of storage, anchovy samples were analysed from a chemical (TVB‐N and TBARS), physical (texture analysis), microbiological (microbial count) and sensory (QIM) point of view and compared to control samples (without the electrostatic field). DENBA+ technology was able to reduce of 20% the QI score increment rate with respect to the control sample justified by a better quality of the samples after 7 days of storage. In addition, loads of spoiling microbes were significantly lower in DENBA+ after 9 days of storage. This non‐thermal technology has shown positive effects for long periods of storage.
•Exploration of energy density sources of variability: species, season, region, size.•Relationships between dry mass content and ED are strong but species specific.•Larger length, mass and ED at age ...in the English Channel than in the Bay of Biscay.•Sardine display larger energy reserves than anchovy.•Larger reserves are likely in link with larger spawning or maintenance costs.•A strong scaling of ED with size with a dome shape pattern for sardine.•Decrease of ED with size is discussed in link with feeding and spawning behaviours.
There is a growing interest in monitoring body condition of marine organisms in the context of the ecosystem approach to fisheries and global change. Fish condition is under the influence of environmental variability on seasonal scale, but also on longer timescales. It represents a good indicator of habitat quality or individual fitness, and is also a relevant parameter to evaluate energy transfer through the trophic chain. However, the sources of variability in fish condition need to be accurately understood and the significance of existing indices has to be correctly assessed. Here, we measured the energy density, a precise and global indicator of fish bioenergetic condition, for anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) in the Bay of Biscay and the English Channel, based on an extensive sampling design in 2014. First, we investigated the well-documented relationship between percent dry mass and energy density, and showed that such relationship is species specific. Second, we observed distinct patterns in bioenergetic condition between anchovy and sardine. Both species display similar minimum values at size or age but maximum are significantly higher for sardine, reflecting a higher energy storage capacity that scales more strongly with size. Third, we confirmed the large seasonal variability in energy density of both species. In the Bay of Biscay, energy density values for anchovy and sardine (age 1+) are 5.7 and 5.9 kJ g−1 (wet weight) in spring and 6.8 and 7.9 kJ g−1 in autumn, respectively. Our results revealed that fish from the English Channel display significantly higher energy density values in autumn (9.8 kJ g−1 for anchovy and 10.5 kJ g−1 for sardine) than those from the Bay of Biscay. When combined with size and weight at age it appears clearly that, after age 1, fish from the northern region display larger growth and energy reserves. This likely results from a higher zooplankton productivity in the English Channel or/and a selection pressure towards faster growing and faster reserve building individuals, to be able to survive a longer winter than in the Bay of Biscay. Finally, we described a dome shaped evolution of energy density with body size in case of sardine. Increase with size has been well documented but not the decrease at largest sizes. Several mechanisms may explain such a pattern, i.e. increasing investment in spawning, shift in diet or a metabolic trade-off between temperature and food availability, with regard to maintenance requirements.
Small pelagic fish species present complex dynamics that challenge population biologists and prevent effective management. Huge fluctuations in abundance have traditionally been associated with ...external environmental forcing on recruitment, exempting other processes from contributing to fisheries collapse. On the other hand, theory predicts that density dependence and overexploitation can increase the likelihood of population oscillations. Here, we combined nonlinear population modeling with Bayesian analysis to examine the importance of different regulatory mechanisms on the collapse of European anchovy (Engraulis encrasicolus) in the Bay of Biscay. The approach relied on detailed population data and in a careful characterization of changes in the environment experienced by anchovy early stages based mainly on satellite remote sensing. Alternative hypotheses about external forcing on recruitment determined prediction skill and provided alternative interpretations of the causes behind the collapse. Density dependence was weak and unable to generate huge oscillations. Instead, models considering changes in phytoplankton phenology or in larval drift presented the best prediction skill. Nevertheless, an extensive surrogate analysis showed that environmental fluctuations alone barely explain anchovy collapse without considering the impact of fishing. Our results highlight the effectiveness of a Bayesian approach to analyze the dynamics and collapse of managed populations.
Identification of the potential habitat of European anchovy (Engraulis encrasicolus) at different life stages in relation to environmental conditions is an interesting subject from both ecological ...and management points of view. For this purpose, acoustic data from different seasons and different parts of the Mediterranean Sea along with satellite environmental and bathymetry data were modelled using generalized additive models. Similarly, egg distribution data from summer ichthyoplankton surveys were used to model potential spawning habitat. Selected models were used to produce maps presenting the probability of anchovy presence (adults, juveniles and eggs) in the entire Mediterranean basin, as a measure of habitat adequacy. Bottom depth and sea surface chlorophyll concentration were the variables found important in all models. Potential anchovy habitats were located over the continental shelf for all life stages examined. An expansion of the potential habitat from the peak spawning (early summer) to the late spawning season (early autumn) was observed. However, the most suitable areas for the presence of anchovy spawners seem to maintain the same size between seasons. Potential juvenile habitats were associated with highly productive inshore waters, being less extended and closer to coast during winter than late autumn. Potential spawning habitat in June and July based on ichthyoplankton surveys overlapped but were wider in extent compared with adult potential habitat from acoustics in the same season. Similarities and dissimilarities between the anchovy habitats as well as comparisons with sardine habitats in the oligotrophic Mediterranean Sea and other ecosystems with higher productivity are discussed.
Ecophenotypic differentiation among replicate ecotype pairs within a species complex is often attributed to independent outcomes of parallel divergence driven by adaptation to similar environmental ...contrasts. However, the extent to which parallel phenotypic and genetic divergence patterns have emerged independently is increasingly questioned by population genomic studies. Here, we document the extent of genetic differentiation within and among two geographic replicates of the coastal and marine ecotypes of the European anchovy (Engraulis encrasicolus) gathered from Atlantic and Mediterranean locations. Using a genome‐wide data set of RAD‐derived SNPs, we show that habitat type (marine vs. coastal) is the most important component of genetic differentiation among populations of anchovy. By analysing the joint allele frequency spectrum of each coastal–marine ecotype pair, we show that genomic divergence patterns between ecotypes can be explained by a postglacial secondary contact following a long period of allopatric isolation (c. 300 kyrs). We found strong support for a model including heterogeneous migration among loci, suggesting that secondary gene flow has eroded past differentiation at different rates across the genome. Markers experiencing reduced introgression exhibited strongly correlated differentiation levels among Atlantic and Mediterranean regions. These results support that partial reproductive isolation and parallel genetic differentiation among replicate pairs of anchovy ecotypes are largely due to a common divergence history prior to secondary contact. They moreover provide comprehensive insights into the origin of a surprisingly strong fine‐scale genetic structuring in a high gene flow marine fish, which should improve stock management and conservation actions.
PDF
