Environmental drivers influencing the abundance of round sardinella (Sardinella aurita) and European sprat (Sprattus sprattus) in different areas of the Mediterranean Sea

WOS:000744169400004International audienceData on Sardinella aurita (round sardinella) and Sprattus sprattus (European sprat) in the Mediterranean Sea are limited due to their scarce commercial interest, at least in European countries. Yet, these two small pelagic fish, sitting at opposite ends of the thermal range, could be interesting sentinel species to monitor the effects of climate change in the basin. Using the Mediterranean International Acoustic Surveys (MEDIAS) - the most extensive source of information on these species - we analysed their biomass in several geographical subareas of the central and western Mediterranean Sea in relation to satellite-derived environmental parameters. Our findings highlight that the S. aurita biomass responded to temperature, salinity, chlorophyll concentration and sea level anomaly, depending on the GSA examined, whereas the S. sprattus biomass correlated significantly with salinity in GSA 6, with salinity and chlorophyll concentration in GSA 7 and with sea level anomaly in GSA 17. These data widen our knowledge of the factors that contribute to the ecology of these species. Further studies of their spatial distribution and of their interactions with other small pelagic species, predators and prey are needed to depict a more comprehensive scenario

Variability in size at maturity of European anchovy (Engraulis encrasicolus) within the Mediterranean Sea

WOS:000739856200001International audienceSize at first sexual maturity (L50) represents an important life history trait in the development of management measures providing fundamental information to avoid the exploitation of younger individuals. L50 is known to display variability due to fishing pressure, geographical gradient and environmental features. In this study, in order to investigate L50 variability among areas of the Mediterranean and Black Sea, maturity ogives of anchovy (Engraulis encrasicolus) were estimated by considering samples collected during the anchovy spawning period in the framework of the MEDiterranean International Acoustic Survey (MEDIAS) program. Anchovy size and sexual maturity data from several Geographical Sub-Areas (GSA) – i.e., Northern Spain, Gulf of Lion, Tyrrhenian Sea, Strait of Sicily, Adriatic Sea and Black Sea – were gathered according to a standard methodological protocol. Maturity ogives were estimated by means of a logistic regression taking into account total length, condition factor, sex and GSA. Obtained results evidenced a significant effect of condition factor, fish in better condition reaching maturity earlier, as well as differences in L50 values among areas and between sexes, with males reaching the maturity at lower length than females. Even though the obtained L50 estimates are relative to the spawning period only, the observed variability at the Mediterranean basin scale highlights the importance to explicitly consider the habitat peculiarities in order to provide management advices based on an ecosystem approach to fishery

Variability in size at maturity of European anchovy (Engraulis encrasicolus) within the Mediterranean Sea

WOS:000739856200001International audienceSize at first sexual maturity (L50) represents an important life history trait in the development of management measures providing fundamental information to avoid the exploitation of younger individuals. L50 is known to display variability due to fishing pressure, geographical gradient and environmental features. In this study, in order to investigate L50 variability among areas of the Mediterranean and Black Sea, maturity ogives of anchovy (Engraulis encrasicolus) were estimated by considering samples collected during the anchovy spawning period in the framework of the MEDiterranean International Acoustic Survey (MEDIAS) program. Anchovy size and sexual maturity data from several Geographical Sub-Areas (GSA) – i.e., Northern Spain, Gulf of Lion, Tyrrhenian Sea, Strait of Sicily, Adriatic Sea and Black Sea – were gathered according to a standard methodological protocol. Maturity ogives were estimated by means of a logistic regression taking into account total length, condition factor, sex and GSA. Obtained results evidenced a significant effect of condition factor, fish in better condition reaching maturity earlier, as well as differences in L50 values among areas and between sexes, with males reaching the maturity at lower length than females. Even though the obtained L50 estimates are relative to the spawning period only, the observed variability at the Mediterranean basin scale highlights the importance to explicitly consider the habitat peculiarities in order to provide management advices based on an ecosystem approach to fishery

Effects of sampling intensity and biomass levels on the precision of acoustic surveys in the Mediterranean Sea

WOS:000744169400002Acoustic surveys represent the standard fishery-independent method worldwide for evaluating the biomass and spatial distribution of small pelagic fish populations. Considering the peculiarities of the spatial behaviour of pelagic fishes, the efficiency of the survey design in determining their biomass and spatial distribution is related to the ability to capture the portion of the patches accounting for a larger part of the total biomass. However, the spatial structure of the patches could be strongly influenced by ecosystem characteristics as well as by changes in total biomass related to a density-dependent mechanism. This is of particular interest for anchovies and sardines, which are known for their wide fluctuations and high sensitivity to the environment. In this study, we analysed the efficiency of acoustic surveys targeting European anchovies (Engraulis encrasicolus) and European sardines (Sardina pilchardus) in 10 different areas of the Mediterranean Sea spanning three years of different biomass levels. Using the geostatistical coefficient of variation (CVgeo) of the average occurrence probability of high/medium density values, we showed different patterns in terms of survey design efficiency among areas and species. Anchovies usually showed a lower CVgeo than sardines in the Alboran Sea. In 4 out of 20 cases, CVgeo values showed a consistent decrease with increasing biomass, while in the remaining cases, the CVgeo did not follow any clear pattern, suggesting the presence of important environmental effects. Higher survey design efficiency was found in highly productive sectors influenced by river run-off, allowing us to hypothesize that higher productivity along with the presence of well-localized enrichment mechanisms could favour a spatially consistent distribution and coherent organization of fish populations, leading to higher precision estimates with a given transect design. While most surveys displayed CVgeo close to 10% or less even at low biomass, indicating generally good performances of the survey design, a few areas exhibited higher CVgeo, yielding a potential need to decrease the intertransect distance, always keeping in mind that any survey should be as synoptic as possible