Natural food and feeding of the commercial blue swimmer crab, Portunus Pelagicus (Linnaeus, 1758) along the coastal waters of the Kingdom of Bahrain

Abstract

The blue swimmer crab Portunus pelagicus has a wide geographical distribution and is an important commercial species throughout the subtropical waters and as such constitutes part of the fisheries resources. Although, local consumption of this species is low, the species support a fast growing industry. They are found inshore on sandy and muddy habitats and among sea grass beds. Data are lacking on the natural diet of Portunids along the coastal waters of Bahrain and the Arabian Gulf. This study investigates the natural diet and feeding of P. pelagicus. The crabs were obtained from local fish-trap catches during 2004, 2005 and 2007. Morphometrics were carried out on 371 individuals but 271 stomachs were used for the stomach fullness analysis and 196 were used in the diet analysis. The difference between sexes and seasonality was assessed using ANOVA and ANCOVA through SPSS v.18. The diet of this species is highly variable reflecting the ability of adopting different modes of feeding. P. pelagicus can be described as omnivorous although, the preference for animal matter was evident. Higher proportion of stomachs had tissues of crustaceans, molluscs and fish compared to plant matter. The occurrence of sediment in over 50% of the stomachs indicates adopting periods of deposit feeding. Many individuals had synthetic fibres and plastics confirming the presence of these pollutants in the surrounding. No significant dietary difference was obtained between the sexes although the trend for greater stomach fullness was apparent in the males. Morphometrically, males were significantly (p ⩽ 0.05) larger than females. Fish and polychaetes were found more frequently in the males than females but these differences disappeared when adjusted for body size (ANCOVA). The difference in stomach fullness over time was significant (p ⩽ 0.05) in particular, between the months of August and June