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Knowing the species-specific target strength (TS) allows converting volume backscattering strength to numerical abundance. Since the acoustic surveys conducted for biomass assessment in the Mediterranean Sea currently focus on the echoes of two or three target pelagic species, the TS of non-target species has seldom been investigated in this basin. This is the first study of the TS of two pelagic species – Mediterranean horse mackerel (Trachurus mediterraneus) and Atlantic chub mackerel (Scomber colias) – in the Mediterranean Sea. A pilot approach using tethered live fish but not involving hooks and anesthetic was tested in experiments using a split-beam scientific echosounder operating at 38, 120, and 200 kHz. The mean TS was estimated for 29 live fish. The relationship between TS and fish length was determined with a standard linear regression model; the b 20 conversion parameter was obtained with the slope forced to 20. b 20 was computed at all frequencies for both species. The key values at 38 kHz were −71.4 dB for T. mediterraneus and −71.6 dB for S. colias. Although these results differ from those obtained with in situ and ex situ experiments using Pacific chub mackerel and other species of the genus Trachurus, they have the potential to provide new reference values for T. mediterraneus and S. colias biomass assessment in the Mediterranean Sea. The proposed method removes some potential biases due to the unnatural behavior of anesthetized fish. Moreover, it provides an alternative to hooks, although the use of a piece of rope instead of the hook seems to increase the acoustic reflectivity of the tethering apparatus.

This paper evaluates the effect of changing from a diamond mesh codend (T0) to a 90° turned mesh codend (T90) on the size selectivity of seven commercially important species in the Mediterranean bottom trawl fishery. In sea trials conducted in the north-western Adriatic, two experimental codends made of 54 mm nominal mesh size netting and differing only in mesh configuration were alternately mounted on the same trawl. Overall, the T90 mesh significantly improved codend size selection for all the species analysed. The difference in the predicted average L50 values between the T90 and T0 codend was particularly marked in European hake ( Merluccius merluccius , 21.26 vs 11.26 cm total length), common squid ( Loligo vulgaris , 12.06 vs 7.88 cm mantle length) and mantis shrimp ( Squilla mantis , 20.78 vs 13.35 mm carapace length). Both codends showed an excessive size selectivity, which involves a commercial loss, especially for red mullet ( Mullus barbatus ), Mediterranean horse mackerel ( Trachurus mediterraneus ) and whiting ( Merlangius merlangus ). These findings demonstrate the efficiency of the T90 configuration in excluding undersized specimens, especially of hake, whose average L50 was above the minimum conservation reference size of 20 cm. The adoption of this practical and inexpensive solution can contribute to improve the management of the demersal resources targeted by the Mediterranean bottom trawl fishery.

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.

Krill, a key pelagic resource of the Antarctic food web, provides an important link between primary and secondary plankton production and top predators. Since krill abundance is a crucial factor in Antarctic ecosystem functioning, its monitoring supplies vital data. Acoustic surveys are an effective approach to estimating krill abundance. An acoustic survey was conducted in the western Ross Sea in January 2014–10 years after a similar survey by our team - to estimate krill abundance and biomass and monitor oceanographic conditions. Antarctic krill ( Euphausia superba ) was detected in the northern part of the western Ross Sea and dense swarms of ice krill ( Euphausia crystallorophias ) were found in its central coastal area. Data analysis revealed an inverse correlation between E. superba density and salinity in the water column, whereas a positive correlation was found between E. crystallorophias abundance and fluorescence; the latter relationship was confirmed in thematic maps of E. crystallorophias spatial distribution and fluorescence. Comparison of 2004 and 2014 biomass data showed a much greater abundance of both species in the more recent survey.

Identification of potential spawning and nursery areas of European anchovy (Engraulis encrasicolus) represents an essential step in the management of a resource which is of fundamental importance both for fishery and pelagic trophic web. Egg and larvae occurrence from ichthyoplankton surveys (2012 - 2015) in the South Western Adriatic Sea were examined to understand the mechanisms that control their distribution. Egg and larvae densities varied through the years with the highest values recorded in 2012 and the lowest in 2014. Positive correlations between eggs and larvae with zooplankton were observed. When quotient analysis was used to find relations with environmental and biological variables, the results pointed out an egg preference for depth between 91 and 120 m and an avoidance between 11 and 30 m. Moreover, egg avoidances for high values of chlorophyll-a (> 0.52 mg m-3) and low values of zooplankton biomass (< 199 mg m-2) were highlighted. On the other hand, different ranges of habitat preferences and avoidances were observed for larvae: preference range of depth between 11 and 60 m and avoidance > 151 m; preference for high zooplankton biomass (> 1000 mg m-2) and avoidance for low biomass (< 299 mg m-2). These correlations and the quotient values suggest that egg and larvae distribution in the South-Western Adriatic Sea is mainly driven by food availability and depth.