Stomach content of three batoid species in the Sea of Marmara of the North-eastern Mediterranean

Abstract

The feeding habits and trophic levels of three uncommon batoid species (Dasyatis pastinaca, Myliobatis aquila, Torpedo marmorata) were investigated in the Sea of Marmara, with two different methodical approaches: stomach content analysis and stable isotope analysis. The stomach contents indicated that the teleost species is the most important prey group for D. pastinaca and T. marmorata, while Mollusca is the main prey group for M. aquila. Niche breadths were calculated 0.54 for D. pastinaca while 0.29 for M. aquila. No significant diet overlap was detected between D. pastinaca and M. aquila (0.21) based on Pianka index. δ15N muscle and δ15N liver values statistically differed between D. pastinaca and M. aquila (Fpseudomuscle=33.736, p=0.03; Fpseudoliver= 26.173, p= 0.01). The trophic levels were 4.20±0.73 for D. pastinaca, 4.04±0.63 for M. aquila and for T. marmorata 4.46±0.79 by stomach content analysis. The trophic levels of species from stable isotope analysis by δ15N were calculated as 3.67 for T. marmorata, 3.32 for D. pastinaca and 2.56 for M. aquila. The difference in trophic levels may be explained by long-term and short-term feeding strategy of these species. Torpedo marmorata and M. aquila have higher δ15N values compared to samples from other regions of the Mediterranean.