Diet of the Silky Shark Carcharhinus falciformis (Müller & Henle, 1839) in Waters off Côte d’Ivoire (West Africa)

Abstract

Aims: This study was to establish the feeding habits of silky shark Carcharhinus falciformis in waters off Côte d’Ivoire.
 Study design: All stomachs of the specimens were collected using a standard method and analysed at laboratory.
 Place and Duration of Study: The study of the diet of C. falciformis was carried out at the laboratory of the Oceanological Research Centre (ORC) between April 2019 and August 2020.
 Methodology: To carry out this study, measurements and extractions of the stomachs of silky sharks were performed using a tape measure and dissection kit. Diet was described using the Index of Relative Importance (%IRI). The food overlap between sexes, size groups and marine seasons were analysed using the Morisita index.
 Results: A total of 265 specimens ranging in size from 79 to 254 cm total length were used. Of the stomachs examined, 163 individuals had food contents (61.51%), whilst 102 were empty (38.49%). The results indicated that silky shark has epipelagic and mesobathypelagic feeding habits, preying upon a wide number of prey taxa (33 species) but with a diet dominated by teleost fishes, especially Thunnus albacares (60.62%IRI) and Katsuwonus pelamis (33.18%IRI). The Morisita index and the Spearman rank correlation coefficient showed similarity of the diet between sexes (Cλ > 0.60; Rs = 0.776 and p = 0.001 and marine seasons (Cλ > 0.60; Rs = 0.658 and p = 0.001). The juveniles and adults did not show any overlap. The Amundsen graphical (Fig. 3) analysis suggested that silky shark displays specialist feeding behaviour in this area.
 Conclusion: Diet consisted mainly of T. albacares and K. pelamis, the proportions of which varied according to size and marine seasons. Carcharhinus falciformis is considered to be a specialist predator.