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Isotopic niche partitioning between two small cetacean species

Cristian Alberto Durante*, Enrique Alberto Crespo, Rocio Loizaga

*Corresponding author:

ABSTRACT: Commerson’s dolphin, Cephalorhynchus commersonii, and Peale’s dolphin, Lagenorhynchus australis, live in sympatry along the Southwestern South Atlantic Ocean, suggesting the existence of some degree of habitat partitioning to reduce their competition for resources. Both species are usually associated with coastal environments, however, information on their trophic ecology is scarce. Here we explore the existence of trophic resource partitioning between these two sympatric dolphin species using δ13C and δ15N. A total of 14 Commerson’s dolphin and 34 Peale’s dolphin skin samples were analyzed from 2007 to 2013 in a Marine Protected Area (MPA) from Argentina. Spatial partitioning was found intra and interspecifically as indicated by significant differences in δ13C values. Three different Peale’s dolphins’ feeding groups (FG) were identified: FG1 exclusively exploited the pelagic habitat, FG2 occupied more pelagic/inshore habitats (similar to the Commerson’s dolphin), and FG3 occupied more benthic/inshore habitats. Isotopic niche breadth varied between species and feeding groups, exhibiting less variation in prey selection among individuals for Commerson’s dolphin. According to SEAB analysis, isotopic niche overlap was found between both feeding groups from 2007-2012 (FG2-FG3), and between FG2 and Commerson’s dolphins. Mixing models suggest that FG3 has a diet mainly based in benthic fish, while FG2 and Commerson’s dolphin are feeding predominantly on pelagic fish. Overall, this study indicated segregation in the use of trophic resources between two sympatric dolphin species, showing different foraging strategies that promote their coexistence and reduce their intra and interspecific competition. Furthermore, the presence of three Peale’s dolphins feeding groups segregated at a small geographic scale, suggests a previously unknown ecological complexity.