Naslov
Influence of sea-bottom temperature and depth on swept area estimation from trawl surveys

Autori
Brčić, Jure ; Grilli, Federica ; Sala, Antonello

Izvornik
Scientia marina (0214-8358) 78 (2014), 1; 135-142

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
swept area ; bottom trawl survey ; net opening ; Mediterranean Sea.

Sažetak
The methodological approach to data collection and analysis in Mediterranean bottom trawl surveys has changed considerably since their beginnings in the mid- 1980s. The introduction of new technologies in surveys greatly improved knowledge on trawl underwater geometry, but also raised a question on the reliability of the data obtained. The most commonly used trawl monitoring systems in the Mediterranean use the constant speed of sound when calculating horizontal distance from one sensor to another. However, the speed of the sound in seawater is not constant because it depends on water temperature, pressure, and salinity. This is known to affect the performance of the horizontally transmitting sonars, and it is reasonable to assume that unless it is properly compensated for, the readings from trawl monitoring systems can be incorrect, resulting in biased swept area estimates, and hence potentially producing bias in abundance estimates. In the knowledge that speed of sound depends on temperature, salinity and pressure, the Del Grosso (1974) equation was used to calculate the compensation coefficient for a series of theoretical depth and temperature data. A simple model is proposed in the current paper for the manual correction of the horizontal net opening and swept area estimates. Temperature and depth data obtained from the MEDATLAS project are used to show seasonal and spatial variation in the near- bottom speed of sound, and the results demonstrate that, unless compensated for properly, the error in the horizontal net spread ranges from –1.5% to 2.9%.

Izvorni jezik
Engleski

Znanstvena područja
Biotehnologija

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