Trophic variation during the early stages of blacktip sharks (Carcharhinus limbatus) within coastal nurseries of the Galapagos Marine Reserve

Abstract

The blacktip shark (Carcharhinus limbatus) is a placental shark that uses coastal nursery areas in the Galapagos Marine Reserve, where juveniles live during their early life stages. To better understand the feeding behavior of early juvenile blacktip sharks, we conducted stable isotope analysis on 57 samples from three coastal nurseries around the archipelago. We evaluated the intraspecific variation in trophic shifts of four size classes (<60, 60–69, 70–79 and ≥ 80 cm TL) based on δ13C and δ15N signatures. No significant differences in δ13C and δ15N values were observed among nursery areas (P = 0.127 and P = 0.736, respectively) nor between sexes (P = 0.881 and P = 0.993, respectively). However, there were significant differences among size classes, with δ13C and δ15N values showing a negative relationship with size (R = −0.54, P = 0.001 and R = −0.60, P = 0.001, respectively). Neonates (TL < 60 cm) exhibited a larger trophic niche, whereas larger individuals (TL ≥ 80 cm) exhibited a reduction in trophic niche as a result of different use of resources. Clustered δ15N signatures for the two largest size classes showed similar feeding patterns and same trophic level, while δ13C signatures in all size classes showed the use of several primary carbon sources. Our results showed trophic variations among early life stages, as a result of maternal reminiscence in neonates and foraging variation in larger size classes across coastal nursery areas. This is baseline information on the feeding behavior of early juvenile blacktip sharks in the Tropical Eastern Pacific.