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)(1998)(1999)(2000)(2001)(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.

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.

European anchovy egg occurrence and density data from summer surveys (1998–2007) and oceanographic data were examined to study the mechanisms that control the spatial distribution of anchovy spawning habitat in the Strait of Sicily. Quotient analysis indicated habitat preference for temperature (18–19°C), bottom depth (50–100 m), water column stability (13–14 cycle h−1), fluorescence (0.10–0.15 μg m−3 Chl a), salinity (37.5–37.6 PSU), current speed (0.20–0.25 m s−1) and density (26.7–26.8 kg m−3, σt). Canonical discriminant analysis identified temperature, column stability and fluorescence as major drivers of anchovy spawning habitat. Three of the 4 years which had lower egg abundance were warmer years, with low values of primary productivity. A geostrophic current flowing through the Strait (the Atlantic Ionic Stream, AIS) was confirmed as the main source of environmental variability in structuring the anchovy spawning ground by its influence on both the oceanography and distribution of anchovy eggs. This 10‐yr data series demonstrates recurrent but also variable patterns of oceanographic flows and egg distribution. A lack of freshwater flow in this area appears to depress productivity in the region, but certain and variable combinations of environmental conditions can elevate production in some sub‐areas in most years or other sub‐areas in fewer years. These temporal and spatial patterns are consistent with an ocean triad theory postulating that processes of oceanographic enrichment, concentration, and retention may help predict fishery yields.

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SUMMARYThis study examined the effects of an acoustic stimulus on the haemolymph and agonistic behaviour of the red swamp crayfish, Procambarus clarkii. The experiment was conducted in a tank equipped with a video recording system using six groups (three control and three test groups) of five adult crayfish (30 specimens in total). After 1h of habituation, the behaviour of the crayfish was monitored for 2h. During the second hour, the animals in the test groups were exposed to a linear sweep (frequency range 0.1-25kHz; peak amplitude 148dB rms re.1μPa at 12kHz) acoustic stimulus for 30min. Exposure to the noise produced significant variations in haemato-immunological parameters as well as a reduction in agonistic behaviour.

The sustainable exploitation of small pelagic fish populations, characterized by short life span and early age at first reproduction, is typically more influenced by the success of annual recruitment rather than by fishing mortality. Recruitment strength, in turn, is related to the high environmental variability characterizing the pelagic fish habitats, able to strongly affect the survival of early stages, from hatching to recruitment. Here, we consider the case study of anchovy (Engraulis encrasicolus) stock in the Strait of Sicily (Central Mediterranean). The interannual fluctuations exhibited over an 18-year long period by this fish population was found to be mainly linked to surface circulation patterns, as far as they are able to control retention/dispersal processes of larval stages. We firstly used Lagrangian simulations to reproduce the fate of anchovy early stages during their planktonic phase. Larval retention indices constructed from the output of the simulations were able alone to explain a large proportion of variance (up to 70%) in yearly biomass of the anchovy population, outclassing the other environmental factors considered in this study. Such results are relevant for fisheries management, for all fish stocks characterized by potentially high vulnerability of early life stages.

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SUMMARY:The northern sector of the Sicilian Channel is an area of favourable upwelling winds, which ought to support primary production. However, the values for primary production are low when compared with other Mediterranean areas and very low compared with the most biologically productive regions of the world's oceans: California, the Canary Islands, Humboldt and Benguela. The aim of this study was to identify the main factors that limit phytoplankton biomass in the Sicilian Channel and modulate its monthly changes. We compared satellite-based estimates of chlorophyll a concentration in the Strait of Sicily with those observed in the four Eastern Boundary Upwelling Systems mentioned above and in other Mediterranean wind-induced coastal upwelling systems (the Alboran Sea, the Gulf of Lions and the Aegean Sea). Our results show that this low level of chlorophyll is mainly due to the low nutrient level in surface and sub-surface waters, independently of wind-induced upwelling intensity. Further, monthly changes in chlorophyll are mainly driven by the mixing of water column and wind-induced and/or circulation-related upwelling processes. Finally, primary production limitation due to the enhanced stratification processes resulting from the general warming trend of Mediterranean waters is not active over most of the coastal upwelling area off the southern Sicilian coast.Keywords: upwelling, Ekman transport, nutrients, chlorophyll a, Mediterranean Sea, Sicilian Channel. RESUMEN: Importancia de los fenómenos físicos y la disponibilidad de nutrientes en el control de la concentración de clorofila estimada por satélite en el área costera de afloramiento del Canal de Sicilia. -El sector norte del Canal de Sicilia es un área de vientos favorables para el afloramiento, lo cual debe favorecer la producción primaria. Sin embargo, los valores de producción primaria son bajos comparados con otras áreas del Mediterráneo y muy bajos comparados con las regiones biológicamente más productivas de los océanos a nivel mundial: California, Canarias, Humboldt y Benguela. El objetivo de este estudio fue identificar los principales factores que limitan la biomasa del fitoplancton y modulan sus cambios mensuales. Comparamos estimas de la concentración de clorofila a basadas en satélite en el estrecho de Sicilia, con las observadas en los cuatro sistemas orientales de afloramiento mencionados anteriormente y en otros sistemas costeros del Mediterráneo en los que el viento favorece los afloramientos (Mar del Alborán, Golfo de León y Mar Egeo). Nuestros resultados muestran que la baja producción primaria es debida principalmente a la baja entrada de nutrientes en aguas superficiales, independientemente de la intensidad del afloramiento causado por el viento. Por otro lado, los cambios mensuales en la producción primaria se deben a la mezcla de la columna de agua y afloramientos asociados al viento y/o procesos de circulación en la zona. Finalmente, la limitación de la producción primaria debida al aumento del proceso de estratificación resu...