Temporal and spatial genetic variation of Engraulis encrasicolus in the Adriatic Sea

Small pelagic fish play a key role in the marine ecosystem, controlling predator abundance and regulating primary production rates by foraging on plankton. Alterations induced at different ecological levels by fishing activities and/or environmental changes are affecting the reproductive success of several small pelagics, including European anchovy (Engraulis encrasicolus), which is a major target of Adriatic mid-water trawl and purse-seine fisheries. In this study, we evaluated short-term genetic changes of the species in the Adriatic Sea by applying molecular markers in three generations samples of European anchovy. Thirteen polymorphic microsatellite markers and a mitochondrial gene were used in cohorts of adults and larvae, collected at three sites in the north-east, central and southern Adriatic Sea in 2015. Furthermore, temporal and spatial genetic variation was assessed by comparing the dataset above with a sample of adult anchovy collected in 2012 at three sites close to those sampled in 2015. Expected heterozygosity was higher in adults than in larvae, suggesting a loss of genetic diversity and uneven reproduction. In addition, comparison of the two datasets demonstrated a change in the anchovy population structure from 2012 to 2015. In the reproductive event of 2015, this change led the two main genetic stocks described in the Adriatic Sea to merge into one. We suggest that the population structure of European anchovy in the north-eastern Adriatic may be influenced by changes in environmental parameters and by periodic alterations in the temporal pattern of population connectivity

The history of hydroacoustic surveys on small pelagic fishes in the European Mediterranean Sea

The study of small pelagic fish by hydroacoustic methods in the Mediterranean Sea began in the Adriatic in the 1950’s. Since 2009, internationally coordinated, extensive, regular surveys have been conducted in the framework of the MEDIAS - Mediterranean International Acoustic Surveys – action, under the EU Data Collection Framework, to provide inputs for the management of small pelagics, particularly European anchovy (Engraulis encrasicolus) and European sardine (Sardina pilchardus). The surveys cover EU Mediterranean waters and monitor the distribution and abundance of small pelagic species using a common protocol. The hydroacoustic surveys, historically conducted by each Country separately, have since been standardized and harmonized. This is a review of the evolution of the surveys from the beginning up to the present and discusses the future prospects. It reports the historical time series of anchovy, sardine and other small pelagics in different areas and describes the spatial and temporal distribution of small pelagic species in decadal maps of the major areas of their distribution in the European Mediterranean Sea. Furthermore, it discusses the use of MEDIAS data for stock assessment purposes, the collection of auxiliary information for an ecosystem-based management approach, the need for further standardization and future challenges.En prensa0,56