Acoustic backscatter of small pelagic fish species in the Adriatic Sea

Palermino, Antonio (2023) Acoustic backscatter of small pelagic fish species in the Adriatic Sea, [Dissertation thesis], Alma Mater Studiorum Università di Bologna. Dottorato di ricerca in Tecnologie innovative e uso sostenibile delle risorse di pesca e biologiche del mediterraneo (fishmed-phd), 35 Ciclo.
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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.

Tipologia del documento
Tesi di dottorato
Palermino, Antonio
Dottorato di ricerca
Settore disciplinare
Settore concorsuale
Parole chiave
Fisheries acoustics, Target Strength, Mediterranean horse mackerel, Atlantic chub mackerel, Sprat, broadband, modelling, Mediterranean Sea
Data di discussione
16 Giugno 2023

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