Carbon and nitrogen isotope discrimination factors in feces, sloughed skin, and milk of common bottlenose dolphins Tursiops truncatus

Abstract

Stable isotope analysis is a valuable tool for understanding the food habits of cetaceans, however, current sampling methods that generate wounds are invasive for small cetaceans in particular. Therefore, it is essential to obtain tissue samples using minimally invasive methods. Furthermore, the diet-tissue discrimination factors required for stable isotope analysis vary among tissues. Hence, we assessed the carbon and nitrogen discrimination factors of the feces, sloughed skin, and milk of captive common bottlenose dolphins (Tursiops truncatus). Fecal samples were collected from dolphins that were fed a variety of fish species, whereas sloughed skin and milk samples were collected from individuals fed only one fish species for approximately 2.5 months. The calculated diet discrimination factors are as follows: Δ13C＝0.43±0.64% and Δ15N＝－1.52±0.55% for feces; and Δ13C＝1.47±0.17% and Δ15N＝1.33±0.36% for sloughed skin; Δ13C＝0.44±0.26% and Δ15N＝1.44±0.17% for milk. These findings suggest that the obtained discrimination factors could be used to investigate the feeding ecology of free-ranging dolphins.