Foraging segregation between spotted (Stenella attenuata) and spinner (Stenella longirostris) dolphins in the Mexican South Pacific

Coexistence among sympatric species requires a certain degree of resource partitioning. In the Mexican South Pacific, information regarding the coexistence of Stenella attenuata (SA) and Stenella longirostris (SL) is lacking. Stable isotope analyses (delta N-15 and delta C-13) were conducted to assess the differences in feeding habits to infer trophic position and amplitude as well as habitat use, based on Bayesian inference and a random forest (RF) classifier. Potential trophic relationships with other species were assessed by Bayesian mixing models. Feeding segregation between species was mainly based on carbon sources (delta C-13: p(SA > SL) = 100%, RF Gini Impurity = 80%). Moreover, SA (n = 22) presented a broader isotopic niche than that of SL (n = 25; SIBER Bayesian Standard Ellipse areas = 0.91 parts per thousand(2) vs. 0.77 parts per thousand(2)) with a 33% overlap, suggesting that SA uses more coastal habitats than SL. The most relevant prey species were the mesopelagic fish Benthosema panamense and the epipelagic fish Hyporhamphus naos (similar to 50%), although B. panamense was more related to SL than SA: p(%SL > %SA) = 76.6%. The trophic positions were 4.0 (SA) and 3.8 (SL). Our results provide evidence of resource partitioning within a potential foraging ground for both dolphin species.

Automated summary

This study investigated the coexistence of Stenella attenuata and Stenella longirostris in the Mexican South Pacific using stable isotope analyses. The results showed that the two dolphin species mainly segregated their feeding habits based on carbon sources, with SA having a broader isotopic niche and using more coastal habitats than SL. The most important prey species were the mesopelagic fish Benthosema panamense and the epipelagic fish Hyporhamphus naos, with B. panamense being more related to SL.