Resolving the Trophic Relations of Cryptic Species: An Example Using Stable Isotope Analysis of Dolphin Teeth

Abstract

Understanding the foraging ecology and diet of animals can play a crucial role in conservation of a species. This is particularly true where species are cryptic and coexist in environments where observing feeding behaviour directly is difficult. Here we present the first information on the foraging ecology of a recently identified species of dolphin (Southern Australian bottlenose dolphin (SABD)) and comparisons to the common bottlenose dolphin (CBD) in Victoria, Australia, using stable isotope analysis of teeth. Stable isotope signatures differed significantly between SABD and CBD for both δ13C (−14.4‰ vs. −15.5‰ respectively) and δ15N (15.9‰ vs. 15.0‰ respectively), suggesting that the two species forage in different areas and consume different prey. This finding supports genetic and morphological data indicating that SABD are distinct from CBD. In Victoria, the SABD is divided into two distinct populations, one in the large drowned river system of Port Phillip Bay and the other in a series of coastal lakes and lagoons called the Gippsland Lakes. Within the SABD species, population differences were apparent. The Port Phillip Bay population displayed a significantly higher δ15N than the Gippsland Lakes population (17.0‰ vs. 15.5‰), suggesting that the Port Phillip Bay population may feed at a higher trophic level - a result which is supported by analysis of local food chains. Important future work is required to further understand the foraging ecology and diet of this newly described, endemic, and potentially endangered species of dolphin.

Use of carbon and nitrogen stable isotopes to study the feeding ecology of small coastal cetacean populations in southern Brazil

“…If this is the case, although the δ 15 N values were similar among the cetacean populations inside and outside of the bay, this does not necessarily mean that they were feeding at the same trophic level. This kind of situation has already been shown in Victoria Bay (Australia), where two cryptic species of cetaceans living inside and outside of the bay were occupying different trophic levels (Owen et al 2011).…”

“…Although the study involves a small number of samples, any available information on the foraging habits of these species is beneficial for establishing conservation measures (Cremer et al 2012, Owen et al 2011. Nonetheless, results found in this study may not represent the diet behaviour of a large population and conclusions should be drawn with caution.…”

“…13,no. 4 fractionation rates (Post 2002, Owen et al 2011). Figure 4 are most likely contributing to the diet of these individuals, although a large variation in δ 13 C values was observed among nearshore Franciscanas.…”

“…In the literature, there are several studies where differences were found in feeding habits of populations of the same species living in distinct habitats: killer whales (Orcinus orca) in the Pacific Northwest on the border between the US and Canada (Ford et al 1998); sea lions (Eumetopias jubatus) in Alaska (Kurle & Gudmundson 2007); and dolphin species in Australia (Owen et al 2011).…”

“…Understanding the feeding ecology of specific species is considered essential in order to implement effective conservation measures (Owen et al 2011). Franciscana individuals from a separate population found in the nearshore area, located outside of the bay, were also included in the analysis in order to check for variation in feeding strategies of the same species in relation to habitat differences (Ford et al 1998).…”