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

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.

Long-Term Monitoring of Diel and Seasonal Rhythm of Dentex dentex at an Artificial Reef

“…Anyway, general inferences can be made on activity rhythms with spatially limited sampling windows (Hansteen et al, 1997;Refinetti et al, 2007;Bu et al, 2016;Gaudiano et al, 2021). Even trawling, which is the more spatially representative tool, is still anyway limited in comparison to the real extent of marine species distributions (Cama et al, 2011;Sonnewald and Türkay, 2012;Ünlüoglu, 2021). Furthermore, Campos-Candela et al (2018) recently reviewed some methods to inference abundance from visual counts with cameras stating that averaged estimates of animal density do not show any substantial improvement after an adequate sampling effort (i.e., number of cameras and deployment time).…”

Technologically-sustained ecological monitoring of a coastal fish community with a highly integrated biological and environmental data

“…In marine ecosystems' monitoring there has always been the duality of temporal or spatial representativeness of collected data [18]. Also, in non-technologically supported methodologies for marine environmental sampling (e.g., SCUBA divers and fishing nets-based methods), the spatial representativeness goes at the expenses of the temporal one [4], [147], including ROV and AUV surveys, the former for the highcosts of vessels limiting sampling replicability and the latter for , limited autonomy; e.g., battery life cycle and duration [18]. A too temporally scattered sampling frequency can bias our perception of species abundances, richness, and overall biodiversity because of species activity rhythms (i.e., displacements at tidally, diel, and seasonally cycles) [63].…”

“…Anyway, general inferences can be made on activity rhythms with spatially limited sampling windows [141]- [144]. Even trawling, which is the more spatially representative tool, is still anyway limited in comparison to the real extent of marine species distributions [145]- [147]. Furthermore, [51] recently reviewed some methods to inference abundance from visual counts with cameras stating that averaged estimates of animal density do not show any substantial improvement after an adequate sampling effort (i.e., number of cameras and deployment time).…”