•Both seasonal and inter-annual variability in body condition strongly depend on age.•The period 2007-2011 is the critical phase of decrease in sardine body condition.•Changes in temperature and ...chlorophyll-a may explain the decrease in body condition.•High levels of Chl-a during the critical phase suggest more complex trohic responses.
In the Bay of Biscay, mean body length and weight of sardines (Sardina pilchardus) have been decreasing since the early 2000s and could severely impact the fishing and seafood industry sector. These trends have no apparent link with fishing pressure, although the latter has been increasing since the late 2000s. As part of an effort to develop suitable assessment and management tools for this stock, we investigated the life-history traits of sardine and analyze its seasonal and inter-annual variations. Based on 14 years of morphometric data from both scientific surveys and professional samples, we analyzed the variability in sardine body condition and its responses to environmental changes. Generalized Additive Models revealed an age-sex specific decreasing trend in body length over the study period, with most of the variability explained by the age class. Linear Mixed Effect Models applied to the body condition evidenced its strong seasonality and an age class specific decreasing trend. Regardless of age class, maximal body condition is reached at the end summer, after the spawning and plankton productive periods. Overall, annual trends in body condition-at-age showed remarkable coherence, with a significant decrease since 2007 for all age classes, suggesting that factors influencing body condition operate at population level. The shift in sardine body condition towards lower values could be broken down into three periods, with a high dependence on surface Chlorophyll-a and sea surface temperature. However, this study highlights that the period supporting the main decrease in body condition is characterized by high Chlorophyll-a, the available proxy for food, which is counterintuitive. Such a result suggests more complex trophic responses involving secondary production, with potential shift in the timing of the production and/or the quality of the food. At the population level, those changes may have a long-term negative effect, with a decrease in body length and important changes in phenology (length at first maturity, reproductive phenology) and potential consequences on sardine population dynamics in the Bay of Biscay.
This work investigated adult-mediated connectivity and spatial population structure of sardine in the European Atlantic waters. The spatial and temporal progress of cohorts was modelled using ...abundance-at-age survey data by area in the period 2000–2016, covering the region from the northern Bay of Biscay to the eastern Gulf of Cadiz. A novel methodology was used to calculate indices of cohort movement between areas. Movement was relatively low between three large regions, the Bay of Biscay, the northern Spanish and Portuguese waters and the Gulf of Cadiz, each hosting a recruitment hotspot. On the other hand, one half of the sardines recruited in North Portugal and a quarter of those recruited in Southwest Portugal moved to northern Spanish waters and South Portugal, sustaining local populations and fisheries. Movement was mainly driven by recruitment strength and, in a less extent, by food availability during fall. The connectivity and dynamic patterns suggest a metapopulation with three weakly connected populations and density-dependent source-sink movement within the northern Spanish and Portuguese waters population. While the weak connectivity does not invalidate the management boundary between the Bay of Biscay and the Iberian Peninsula, the Gulf of Cadiz may be treated as a separate stock. Multi-area/metapopulation assessment approaches should be applied to account for complex population structure, the higher risks of depleting source areas and/or less productive populations.
Age and size at maturation appear as key parameters governing the dynamics of a population as they affect growth rate, fecundity, and survival. The expression of such life history traits is ...determined by genetic make-up and modulated by environmental factors mainly through phenotypic plasticity. Moreover, fishing, besides decreasing population size and changing demographic composition can alter allelic frequencies through fisheries-induced evolution by selecting for some particular traits. In the Bay of Biscay, a decreasing trend in both sardine body condition and size-at-age has recently been pointed out at the population level. The Probabilistic Maturation Reaction Norm (PMRN) approach was applied to help disentangle phenotypic plasticity and genetic changes. Based on the analysis of sardine spawning seasonality, PMRN was estimated by considering body condition as additional life-history state variable to predict the onset of maturation. The resulting PMRN was then used to investigate temporal trends in reaction norm midpoints to test whether changes in length at maturation can be explained by plastic and/or evolutionary adaptive change. Overall, our results emphasize for the first time that including sardine body condition as explanatory variable improves predictions of maturation probability. We found that better individual condition increases maturation probability. The assessment of temporal changes in length at maturation confirms the low plasticity in this trait for a species maturing mostly at age-1 and advocates for the use of a monthly time scale when investigating PMRNs for this species. Beside environmental variables included in this analysis (water temperature, chlorophyll-
a
, and population biomass) that only show a weak correlation with PMRN midpoints, our results reveal no evidence for recent fisheries-induced evolution in the sardine stock of the Bay of Biscay. They suggest that the short-term variability in length at maturation is strongly dependent upon individual growth which is likely driven by environmental factors. For sardine fisheries management, our study highlights the need to consider both the length-composition data and the seasonality within a stock assessment model. Finally, we discuss the fact that considering individual growth trajectories should improve our understanding of the relationship between environmental variability and changes in maturation for sardine.
This paper describes a methodology that combines meta-population theory and stock assessment models to gain insights about spatial heterogeneity of the meta-population in an operational time frame. ...The methodology was tested with stochastic simulations for different degrees of connectivity between sub-populations and applied to two case studies, North Sea cod (Gadus morua) and Northeast Atlantic sardine (Sardina pilchardus). Considering that the biological components of a population can be partitioned into discrete spatial units, we extended this idea into a property of additivity of sub-population abundances. If the additivity results hold true for putative sub-populations, then assessment results based on sub-populations will provide information to develop and monitor the implementation of finer scale/local management. The simulation study confirmed that when sub-populations are independent and not too heterogeneous with regards to productivity, the sum of stock assessment model estimates of sub-populations' SSB is similar to the SSB estimates of the meta-population. It also showed that a strong diffusion process can be detected and that the stronger the connection between SSB and recruitment, the better the diffusion process will be detected. On the other hand it showed that weak to moderate diffusion processes are not easy to identify and large differences between sub-populations productivities may be confounded with weak diffusion processes. The application to North Sea cod and Atlantic sardine exemplified how much insight can be gained. In both cases the results obtained were sufficiently robust to support the regional analysis.
As an industry based upon the harvesting of wild resources, the fishery is often used in economics to showcase the effects of its specific nature on human behavior and the impacts of that behavior on ...the fish stock itself. The common-pool status usually encountered in the use of these resources makes them especially vulnerable to major shifts in the supporting ecosystems, but also to rapid technical change. In most other parts of the economy, technical change and the creative destruction that it brings along are viewed positively, and even given central role in recent theories of growth. Happily for the creatures of the ocean that are hunted, fishers do not fit the mould of Schumpetarian entrepreneurs bent on creative destruction. However, the technology that does drift onto boats has had concerning effects on the status of fish stocks with important economic and cultural consequences. We present a narrative of the French sardine fishery using the evolutionary theory of technical change. The wild binary segmentation approach was applied on a time-series of French sardine landings from 1900 to 2017. This analysis revealed three significant production change points associated with important technical changes in the fishery. The first change point, in 1927, is related to the introduction of the purse-seine in France. The introduction of the mid-water trawl is the second change point in the early 1970s. A third change point occurred in 1998, where we see a reswitch from mid-water trawl to purse-seine. Collectively, these results highlight the technological changes in sardine production that occurred, but more importantly, the impacts of these changes both on the structure of the population of sardines, and on the industry. The lesson we derive from this case study is that technical change should be considered as a succession of shifts rather than a unidirectional history.
•The PELGAS integrated survey conducted since 2000 in spring in the Bay of Biscay is presented.•PELGAS objectives have switched from the study of the anchovy stock status to ecosystem ...monitoring.•Spatially-explicit data of the main pelagic ecosystem components have been collected since 2000.•Multidisciplinary collaborative working and enough vessel space were critical success factors.•Finding relevant common scales is essential to analyse ecosystem data within or across compartments.
The Pélagiques Gascogne (PELGAS) integrated survey has been developed by a multidisciplinary team of Ifremer and La Rochelle University scientists since 2000, joined by commercial fishermen in 2007. Its initial focus was to assess the biomass and predict the recruitment success of anchovy in the Bay of Biscay in spring. Taking advantage of the space and versatility of R/V Thalassa II, sampling has been progressively extended to other ecosystem components. PELGAS therefore further developed the second objective of monitoring and studying the dynamic and diverse Biscay pelagic ecosystem in springtime. The PELGAS survey model has allowed for the establishment of a long-term time-series of spatially-explicit data of the Bay of Biscay pelagic ecosystem since the year 2000. Main sampled components of the targeted ecosystem are: hydrology, phytoplankton, mesozooplankton, fish and megafauna. The survey now provides two main ecosystem products: standard raster maps of ecosystem parameters, and a time series dataset of indicators of the Bay of Biscay pelagic ecosystem state. They are used to inform fish stock and ecosystem-based management, and support ecosystem research. The present paper introduces the PELGAS survey, as a practical example of an integrated, vessel-based, ecosystem survey. The evolution of the PELGAS scientific team and sampling protocols are presented and analysed, to outline factors crucial to the success of the survey. Data and results derived from PELGAS are reviewed, to exemplify scientific questions that can be tackled by integrated ecosystem survey data. Advantages and challenges of the survey are discussed and put into the context of marine ecosystem surveys in the European Marine Strategy Framework Directive and the Common Fisheries Policy.
•A method for selecting relevant ecosystem indicators is applied to PELGAS integrated survey.•River plume, bottom temperature, phyto & mesozooplankton selected as hydrobiology indicators.•Small ...pelagic fish species appear to have followed distinct trajectories over the last 15 years.•A marked decrease in mean weights of age 1 & 2 anchovy and sardine over the last 15 years is highlighted.•Low impact of fishing and no effect of climate forcing on pelagic ecosystem in spring are confirmed.
This paper is a practical contribution to two important debates raised by the implementation of marine ecosystem based management: (i) which ecosystem data can be provided by a fisheries survey optimised for ecosystem monitoring; and (ii) how to combine/select potential indicators to derive useful information on marine ecosystem status and dynamics? A suite of 143 potential indicators, including spatial indices, representing small pelagic fish and their biotic and abiotic environments are presented. Indicators were routinely derived from the PELGAS integrated ecosystem survey conducted in spring in the Bay of Biscay (BoB). The general patterns over time in this suite of 5–16 years, non-stationary time series are characterised using a methodology based on min–max autocorrelation factors (MAF), to select the most continuous indicators within, and across, several ecosystem components: hydrology, phytoplankton, mesozooplankton, small pelagic fish and megafauna. Potential interactions between selected indicators and external forcing variables, including climate and fishing, were assessed. The results confirm the importance of river discharges, bottom temperature, chlorophyll-a and mesozooplankton biomass in the dynamics of the BoB pelagic ecosystem. Small pelagic fish species appear to have followed distinct trajectories during the last 15 years. A marked decrease in anchovy and sardine mean weights at ages 1 and 2 over the last 15 years was highlighted; potentially caused by density-dependent competition. The quasi-absence of significant correlation between selected survey indicators and climate and fishing pressure proxies suggests a moderate exploitation rate of small pelagic fish resources, and confirms the so far limited effects of large-scale climate forcing on the BoB pelagic ecosystem. Perspectives for the assessment of marine ecosystem status on the basis of suites of indicators derived from integrated ecosystem surveys are discussed.
This paper summarizes the lessons learnt for the management of small pelagic fish from the case study of managing the international fishery on the Bay of Biscay anchovy. A constant catch regime ended ...up with a fishery crash and closure (2005–2009) after a series of recruitment failures. Precautionary advices had been disregarded due to their inability to predict the size of the population during the first half of the year when the major fishery takes place. The crash triggered the EU to develop a long-term management plan in 2008. In the absence of a recruitment indicator, biological risk was minimized through a close coupling between assessment, advice and management, changing the management year to start just after the spring surveys on adults. A major improvement arrived in 2014 by the incorporation of an early recruitment indicator from an autumn acoustic survey on juveniles. This allowed additional exploitation of the resource at similar risk levels. Accordingly, TACs are nowadays set after the recruit survey on a management calendar basis. The interactive collaboration between fishers, scientists, and managers allowed inclusion of the stakeholders’ preferences for a biomass-based catch bounded harvest strategy suitable for these valuable fisheries. This strategy allows catches between a minimum and maximum TAC level, to account for an economically viable minimum activity when approaching a minimum biomass threshold level, and for the limited market absorption capacity when exceeding an upper biomass threshold level, respectively. Such strategy was adopted by consensus and supposed a successful participatory process in fishery management.
•Managing Small Pelagic Fish (SPF) needs a close coupling between assessment, advice and management.•Optimal management of SPF is achieved by including a recruitment indicator•Without a recruitment indicator, then start management after the adult surveys.•Interactive participatory processes allow customizing HCRs to the fishery characteristics and stakeholders’ preferences.•Biomass-based catch bounded HCRs help to harmonize sustainability with fishers’ catch and economic expectations.
•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.
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