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Monochromatic acoustic recognition of scattering layers: case studies in the Turkish seas

Mutlu E.

Hydroacoustics

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2005

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Vol. 8

125-136

EN

One of the major problems in bioacoustics, direct identification of organisms at species level was reviewed with comparison between modern acoustic-based statistics (algorithms, multivariate analyses, scattering models) and observatory acoustics on behavioral natures ascertained to the species (diel vertical migration, response to ambiance, school shapes). Modern biacoustics promise surely gate soon to fulfill solution of the problems. Presently, current acoustical knowledge required behavioral characterization identical to organisms targeted for direct identification. Integrating such techniques with previously obtained background knowledge on characteristics specific to certain organisms, acoustic techniques allow a significantly larger area of the ocean interior to be surveyed at a quite finer resolution on ecology of the scatterers than conventional methods. For instance, Calanus euxinus (copepod) and Sagitta setosa (cheatognath) have distinct patterns of vertical migration and time spent swimming, depending on the DO concentration of the water column in the Black Sea.

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Acoustical (Echosounder and ADCP) observation of Calanus euxinus and Sagitta setosa in the Black

Mutlu E.

Hydroacoustics

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2004

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Vol. 7

163-172

EN

Since direct acoustical recognition of concentration layer of copepods C. euxinus, swimming trajectories of chaetognaths S. setosa in the Black Sea were studied using an echosounder at 120 and 200 kHz and ADCP (Acoustic Doppler Current Profiler) at 150 kHz. Sagitta setosa were acoustically discriminated with respect to vertical migration and vertical distributional range depending on stage status in months. C. euxinus were acoustically discriminated with respect to vertical migration and swimming speed, according to dissolved oxygen (DO) concentration and the timing of migrations. Upward migration was completed in about 3.5 h, starting 2.5 h before and ending 1h after sunset (average rate: 0.95 cm s-1) in summer. Species ascended discretely from the suboxic to the lower boundry of the cold intermediate layer (CIL) at 0.82 cm s-1, and passed up the CIL and thermocline fast (2.3 cm s-1). Downward migration took less time (2 h), starting ~1 h before and ending ~1 h after sunrise. Swimming speed within the thermocline and CIL was 2.7 cm s-1; copepods subsequently returned to daylight depth at a sinking speed of 0.57 cm s-1. Chaetognaths were migrated daily between subsurface and oxycline or suboxic zone (OMZ). The lower limits changed to be the oxycline and OMZ depending on abundance of adult and immature (young) individuals in the concentration layer. In July and September, individuals of a new generation did not migrate and stayed in subsurface water. During January through May, all adults exhibited diel vertical migration and co-existed with the copepod C. euxinus during the day time in the OMZ while during June through October, two different layers of S. setosa underwent during their diel vertical migration: The upper layer was immature individuals and the lower layer was mature individuals.

3

Distribution and discrimination of anchovy, and sprat in the Black Sea from high frequency sound records

Mutlu E.

Hydroacoustics

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1999

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Vol. 2

27--31

EN

High frequency (200 kHz) was used to identify anchovy, and sprat schools from over the entire trackline of broad-scale acoustical survey over a period of 4 years (1991-1994) in the Bleak Sea. Analysis of color enhanced echograms as well as trawl catches provided detailed morphological descriptions to discriminate aggregations of anchovy, and sprat together with characteristics of their habitat. Sprat showed fish school scattered in relatively, a thin layer near the bottom like semi-pelagic fish made up. Anatomy of the aggregation did not change between day and night, and there was 110 diet shift in the habitat. Anchovy formed the pole shaped schools as well as compact aggregation arising from bottom around the shelf break area to that as much high up as 30-70 m, during the day. Additionally, a striking point is that the anchovy in an appearance, of what looked to be pole shape school, stand ready on top of submarine steep cliff to escape down immediately in case of any disturbance to the school. There is a sharp discrimination between the schools of sprat and anchovy.