Diel Variability in the Bottom-Trawl Catch Rates of Sparid Fishes in İzmir Bay (Central-Eastern Aegean Sea)

Aydın Ünlüoğlu

doi:10.28978/nesciences.1036842

Abstract

Time of day may affect the availability, distribution and behaviour of many fishes, at least in the depths that the light penetrates. Changes in the activity and position of the demersal fish as a response to the changing light levels during a diel (24 h) cycle may affect their catchability or vulnerability to the bottom trawl. Diel variability in the bottom-trawl catch rates of five sparid fish species, namely Boops boops, Diplodus annularis, Diplodus vulgaris, Pagellus acarne and Pagellus erythrinus, were investigated during seven experimental bottom-trawl surveys conducted within the same locality in İzmir Bay. All trawl haulings were performed using the same operation and sampling procedure and carried out for each seasonal survey at different periods day, including the morning, noon, afternoon, dusk, early-night, midnight, late-night and dawn. Percentage contribution by weight of the sparid fishes to the total catch varied according to the sampling season between 23-79%. Catch rates of the sparid fishes usually did not show significant diel periodicity except D. vulgaris. Daylight catch rates of D. vulgaris were significantly higher than twilight and night periods (Daylight>Twilight>Night). Information on diel variations obtained in this study could be fundamental in understanding the distribution dynamics of the five sparid fishes and developing future management approaches.

Highlights

Bottom-trawl surveys are used worldwide to estimate the biomass of demersal fish species (Francis & Williams, 1995; Petrakis et al, 2001)
This study aims to provide information on how the bottom-trawl catch rates of sparid fishes vary over a 24 h cycle by considering the daylight, night and twilight periods and whether the sampling seasons affect diel variability in the catch rates
Sparid fishes caught in the study area throughout the bottom-trawl surveys were: B. boops, D. annularis, D. vulgaris, P. acarne, Pagellus bogaraveo, P. erythrinus, D. maroccanus, S. aurata and S. maena

Summary

Introduction

Bottom-trawl surveys are used worldwide to estimate the biomass of demersal fish species (Francis & Williams, 1995; Petrakis et al, 2001). In the Mediterranean Sea, investigations on the demersal fish assemblages primarily focused on the seasonal and/or depth-related changes (Relini et al, 1999; Ungaro et al, 1999; Kallianotis et al, 2000; Labropoulou & Papaconstantinou, 2000; Colloca et al, 2003; Gaertner et al, 2005). The majority of the bottom-trawl data have been collected by diurnal surveys, and information on the composition and distribution pattern of demersal fish assemblages in the dark period is very limited.

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