History of hydroacoustic surveys of small pelagic fish species in the European Mediterranean Sea

Abstract

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.

Understanding the Dynamics of Ancillary Pelagic Species in the Adriatic Sea

“…This confirms the possibility that the use of landing data can be misleading for the evaluation of this stock, whereas the use of survey data, annually collected using a defined systematic scheme, seems the best source of information for estimating the status of this stock. However, it has to be mentioned that acoustic surveys underwent some modifications over the years (Leonori et al, 2021), e.g., the use of different vessels, different sampling times between the eastern and western sides, and a shift in the survey period of the western acoustic survey. The presence of these variables does not allow for easily combining the different surveys, suggesting the need for a standardization protocol to derive a single survey index to be used in stock assessment models.…”

“…The survey period is in summer (June-September), although in some years and areas it has been shifted to early autumn. The ECHOADRI and the PELMON surveys represent the ancestors of the MEDIAS survey; before 2009, no acoustic common protocol was available in European waters, however at a national level research institutes carried out acoustic investigations using a methodology comparable to the one used in the MEDIAS surveys that was derived by the harmonization of the national protocols (Leonori et al, 2021).…”

Drivers of the North Aegean Sea Ecosystem (Eastern Mediterranean) Through Time: Insights From Multidecadal Retrospective Analysis and Future Simulations

“…Data from seasonal bottom trawl surveys from the period 1991-1993 (Labropoulou and Papaconstantinou, 2000;Labropoulou and Papaconstantinou, 2004), were used to estimate the biomass of demersal and benthic fish as well as that of some megafaunal benthic/demersal invertebrates using the swept-area method (i.e., estimation of biomass per area sampled by trawling), in line with Tsagarakis et al (2010). For small pelagic fish, in the absence of surveys during the model period, average biomass estimates were extrapolated from acoustic surveys in a succeeding period (Tsagarakis et al, 2015;Leonori et al, 2021). Dolphins' biomass was updated with recent estimates from aerial surveys (Tsagarakis et al, 2021), macrozooplankton biomass was updated based on Frangoulis et al (2017), while biomass values from the 2000s model were retained for the few remaining FGs (mainly some plankton groups, benthic invertebrate groups and Loggerhead turtle and Sea birds; Supplementary Material Table S1).…”

“…The North Aegean Sea Ecosim module was parameterized after fitting the model to time series for the hindcast period. Specifically, the time series included (i) relative biomass for 17 fish, decapod and cephalopod FGs from bottom trawl (MEDITS; Spedicato et al, 2019) and acoustic (MEDIAS; Leonori et al, 2021) surveys in the area, as well as (ii) catches for 25 FGs which were estimated from landings (ELSTAT, 2021) and discard ratios from DCR/DCF (Supplementary Material Table S4).…”

Observation of Abrupt Changes in the Sea Surface Layer of the Adriatic Sea

“…Therefore, vertical measurements with a calibrated CTD sonde are used to update the parameters of scientific echosounders during acoustic surveys and to collect accurate acoustic data on acoustic targets, which are recorded in echograms. In addition, environmental parameters affect the spatial distribution of small pelagic fishes and, consistent with the survey protocol, a network of CTD stations will also be sampled during hydroacoustic surveys to describe important oceanographic features of the area under study [24].…”