New records of smallscale codlet, Bregmaceros nectabanus Whitley, 1941 (Gadiformes: Bregmacerotidae), in the Adriatic Sea

Six specimens of Bregmaceros nectabanus were collected during the acoustic survey MEDIAS in two consecutive years, off Termoli (Italy) in 2020 and in Albanian waters in 2021, during two night shallow hauls. We report the northernmost record of the alien species in the Mediterranean Sea (Northern Adriatic Sea, FAO fishing area 37.2.1) and one of the highest number of individuals caught in a single haul. This finding testifies a recent geographical spread to the eastern Mediterranean Sea from its distribution area in the Indo-Pacific Ocean and Red Sea, reaching the Adriatic Sea during the 2019. Our records support the hypothesis of a possible establishment of B. nectabanus in this basin

Workshop to scope and preselect indicators for criterion D3C3 under MSFD decision (EU) 2017/848 (WKD3C3SCOPE)

The workshop to scope and preselect indicators for Descriptor 3 criterion 3 under MSFD Commission Decision (EU) 2017/848 (WKD3C3SCOPE) provided a platform for experts from the EU member states and relevant regional bodies to meet and support development and progress the assessment methodology, based on a request by the EC (DGENV). WKD3C3SCOPE is the first of a series of three workshops (WKD3C3THRESHOLDS and WKSIMULD3) to provide guidance in relation to operational indicators for MSFD D3C3. The workshop was organized as a series of presentations with intermittent group discussions. On the first day of the workshop the participants discussed what defines a ‘healthy population structure’ for species with different life history traits (ToR a). During the following days, the group discussed and identified relevant D3C3 indicators (ToR b) and developed criteria to select among the identified D3C3 indicators to allow further testing and setting of thresholds at WKD3C3THRESHOLDS (ToR c). The participants found that overall, healthy fish stocks are characterized by high productivity, wide age and size structuring in the population, and the ability to quickly recover from disturbances. The groups noted that environmental factors, along with stock biomass and fishing pressure, influence the productivity and health of a stock, with environment playing a particularly large role in the recruitment of short-lived stocks. It was suggested that the age structure of a stock might be more relevant for evaluating the health of long-lived stocks. However, it was acknowledged that not all stocks have sufficient data to evaluate all proposed indicators, and a single indicator is unlikely to suffice for all stocks. Data availability, species- specific factors and regional or sub-regional variation are thus also important considerations. In relation to ToR b, the participants presented their work on potential indicators including: recruitment time-series, proportion of fish larger than the mean size of first sexual maturation, F rec/Fbar, length distribution L 90, relative proportion of old fish above A 90, indicators of spawner quality, and SSB/R. A discussion on pros/cons, benefits to the population of high or low indicator values, benefits supported by empirical evidence, applicability to data-poor stocks and benefits supported by simulation/theoretical considerations followed the presentations. Finally, in relation to ToR c, the difficulty emerged in ranking the indicators alone without considering the data used to estimate them and a new set of evaluation criteria for use in WKD3C3THRESHOLDS were defined. Based on the outputs of the meeting a list of indicators to be further evaluated has been drafted, which also emphasizes the stocks for which studies have empirically demonstrated effects on productivity. In addition to the listed indicators, indicators of genetic diversity and proportion of fish with parasite infestation were mentioned but to the knowledge of the participants, widespread data for these are currently not publicly available.info:eu-repo/semantics/publishedVersio

Un approccio integrato per lo studio degli spostamenti e della pesca dei palombi (Mustelus mustelus e Mustelus punctulatus) nel Mar Adriatico

Le popolazioni di elasmobranchi sono in declino nel Mar Mediterraneo: anni di sfruttamento hanno causato la scomparsa dei grandi squali nel mar Adriatico e si sta assistendo ad un declino anche della maggior parte dei piccoli squali bentonici. In questo studio è stato utilizzato un approccio integrato per comprendere gli spostamenti, alcuni tratti della life-history e l’impatto della pesca sulle specie Mustelus mustelus e Mustelus punctulatus nel Mar Adriatico. È stata effettuata un’analisi dei principali indici di pesca e sono stati effettuati campionamenti presso i mercati ittici delle marinerie di Chioggia e Rimini per valutare la composizione del pescato. Questi risultati, insieme alla valutazione dello sbarcato mensile di sei marinerie ed all’integrazione dei dati delle due campagne scientifiche MEDITS e BYCATCH mi hanno permesso di ricostruire la distribuzione e gli spostamenti delle due specie nel Mar Adriatico. M. mustelus e M. punctulatus sono risultate essere le due principali specie di elasmobranchi nei mercati ittici indagati rappresentando rispettivamente il 70% e l’80% delle catture. Analizzando il quantitativo di sbarcato dal 1998 al 2016 si è osservato un aumento delle catture, composte prevalentemente da individui immaturi. L’areale di distribuzione delle due specie arriva a sud fino a circa 42.500° di latitudine, ma i maggiori indici di abbondanza sono stati registrati nella parte più settentrionale del bacino. Questi risultati dimostrano un pattern di spostamento stagionale: gli esemplari migrano verso nord in primavera, per poi spostarsi nuovamente più a sud in tardo autunno, dove permangono per tutto l’inverno. Il drastico calo che hanno subito le specie del genere Mustelus nel Mar Mediterraneo occidentale sottolinea l’importanza di monitorare queste popolazioni nel resto del bacino. Lo studio degli spostamenti e la valutazione della composizione dello sbarcato sono fondamentali per sviluppare delle corrette misure di gestione nel Mar Adriatico

Acoustic backscatter of small pelagic fish species in the Adriatic Sea

The aim of the present study is to apply a broad range of techniques to increase the knowledge of acoustic properties of Sprattus sprattus, Scomber colias and Trachurus mediterraneus in the Adriatic Sea. A novel study using tethered live fish but not involving hooks and anesthetic was tested on T. mediterraneus and S. colias through several ex situ experiments using a split-beam scientific echosounder operating at 38, 120, and 200 kHz. The mean TS was estimated for 29 live specimens, resulting in a conversion factor b20 value of -71.4 dB re 1 m2 and -71.6 dB re 1 m2 respectively which is ~3 dB lower than the current one in use in the Mediterranean Sea. Successively, two monospecific trawl hauls were analyzed through the application of in situ approach for the computation of TS values of S. sprattus which led to six b20 values for sprat (range, -68.8 dB re 1 m2 to -65.6 dB re 1 m2), all higher than the current known value of -71.7 dB re 1 m2. The high difference up to 4.2 dB compared to the current value translates in a significant decrease of absolute sprat biomass along the time series un to 20%. Finally, 149 specimens of the three species were collected for backscattering model application(i.e. Kirchhoff-ray mode model (KRM) and Finite Element Method (FEM)) from digital images of the fish body and swimbladder obtained from Computer Tomography (CT) and X-Ray scans. The values resulting from the application of KRM and FEM are in agreement with empirical results. In general terms the present work proposes the acoustic backscatter characterization of S. colias, S. sprattus and T. mediterraneus in the Mediterranean Sea

Application of backscattering models for Target Strength measurement of Trachurus mediterraneus and Scomber colias in the Mediterranean Sea

In this study, X-Ray and Computer Tomography scans were performed on 82 individual fish collected during the Mediterranean International Acoustic Survey (MEDIAS) 2020 and 2021 carried out in the Adriatic Sea (Mediterranean) [8] for the application of backscattering models. The DICOM files were processed with Image J - 3D slicer and 3D Doctor software to get accurate morphometric characteristic measurements of swimbladder and fish body from 2D and 3D digital images, which were settled as input data for Kirchhoff ray mode model (KRM) and Finite Element Method (FEM) (Figure 1). KRM model accounts for resonant and geometric backscatter using a low mode solution and Kirchhoff-Ray approximation to sum the energy of consecutive gas-filled and fluid-filled cylinders of 1 mm thick [9]. KRM is an analytical model that approximates the shape of the body and swimbladder, hence does not require extensive computation [10]

Application of an analytical approach to characterize the target strength of ancillary pelagic fish species

Abstract The lack of data on the species-specific Target Strength (TS) on ancillary species limits the application of acoustic surveys in assessing their abundance and distribution worldwide. The TS values of Scomber colias and Trachurus mediterraneus in use in the Mediterranean Sea rely on studies conducted on other species in the Atlantic and Pacific oceans. Nevertheless, the application of backscattering models offers the possibility to overcome the absence of empirical data handling the parameters that most affect the TS. X-ray scans were performed on 82 specimens to get digital representations of the swimbladder and the fish body which were used as input for the application of the Kirchhoff Ray Mode model to measure the TS as a function of frequency and tilt angle. The morphometric differences between the two species produced divergent relative frequency responses and broadband TS patterns. Moreover, comparing the results with one ex-situ experiment, we found a good agreement considering a mean tilt angle of − 10°, standard deviation = 12°. Our results provide the first theoretical insights into the use of backscattering models as a tool to distinguish between species in the Mediterranean Sea by acoustic method, increasing the knowledge of the acoustic reflectivity of ancillary species

Biodiversity of Gelatinous Organisms in the Western Adriatic Sea and Identification of Their Echo Traces in Acoustic Data

The abundance of gelatinous organisms, such as salps and jellyfish, in the Adriatic Sea has significantly increased over the past decade. Environmental factors play a key role in driving this shift in abundance through rising temperatures and a consequent decrease in oxygen levels in the water, for which jellyfish have higher tolerance levels. Additionally, fisheries may contribute to the proliferation of jellyfish by diminishing their natural predators and food competitors. Pelagic trawl catch data from 2015 to 2023 acquired during MEDIAS acoustic surveys in the western Adriatic Sea were reviewed to extract information concerning the abundance and distribution of salps and jellyfish. These data were subsequently analyzed and compared with satellite environmental information to identify potential correlations. When considering environmental information related to the month of the survey, the results show two significant relationships: one between the abundance of Aequorea aequorea and average salinity and another one between the abundance of Rhizostoma pulmo and bottom temperature. Furthermore, when considering environmental data from the month preceding the survey, a relationship between the overall abundance of gelatinous organisms, salps and jellyfish together, and surface temperature was identified. Additionally, an analysis was conducted on specific hauls that almost exclusively yielded jellyfish, with the aim of identifying their echo traces. Although it was not possible to allocate one jellyfish species to a specific echo trace due to the frequent co-occurrence of more than one species, a general indication of typical backscatter for these species, with a higher response at 70 kHz, was consistently observed in all cases examined