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.

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Under the general framework of existing recruitment hypotheses, knowledge on the drivers and mechanisms involved in the determination of the year class strength of small pelagic fish (SPF) is briefly reviewed with focus on selected aspects of the adult and larval stages, related to breeding patterns, egg production, spawning habitats, reproductive potential and early life survival. An analysis of stock−recruitment time series data is carried out, showing that the maximum recruitment capacity of clupeoid stocks increases with the strength of temporal autocorrelation in recruitment (R) and decreases as the coefficient of variation of R becomes larger. Reproductive strategy in combination with the thermal and trophic conditions of the ecosystem and the life cycle pattern of the stock can influence the relative importance of high and low frequency variability in recruitment that combine to generate the population fluctuations of SPF. Selective fishing can reduce the reproductive potential and alter the spawning phenology of the stocks. To understand the ways by which the distribution, abundance and survival of larval stages are influenced by trophodynamic and physical factors, it is important to recognize all those milestones in fish ontogeny associated with significant changes in capabilities and behavior (e.g. onset of schooling). Temperature affects many parameters related to egg production and early life survival, but the relative importance of such temperature effects is expected to differ substantially in contrasting SPF habitats.

De novo vitellogenesis is common among teleosts; however, its dynamics and the timing of batch recruitment are poorly understood. In this study, we combine a suite of methods and theories in fish reproductive biology (oocyte packing density, stereology, ovarian allometry, oocyte size frequencies and postovulatory follicle [POF] ageing) to reconstruct the steps and timing of batch recruitment in European anchovy. Using general linear modelling to standardize oocyte numbers, we demonstrate that the fractions of primary growth, cortical alveoli and vitellogenic oocytes in the ovary are relatively stable in females with migratory nucleus oocytes (MN) or with POFs 1 and 2 days old (POF-1 and POF-2), but they change abruptly at hydration. These results imply that batch recruitment in European anchovy occurs in pulses of very short duration (less than a day). The standing crop of vitellogenic oocytes in MN, POF-1 and POF-2 females equals the number of eggs contained in two mature batches.