Potential Residence and Coexistence Strategy of Tursiops truncatus in a Coastal Lagoon in the Southern Gulf of Mexico: Ecological Inferences Using Stable Isotopes

The Terminos Lagoon Flora and Fauna Protection Area is the largest coastal lagoon in the southern Gulf of Mexico and has the largest population of bottlenose dolphins, Tursiops truncatus, reported in the region. Photo identification studies have reported permanent and seasonal residence of dolphins; however, how dolphins coexist ecologically is unknown. In the present study, from 17 dead specimens stranded on the coast of Isla del Carmen (barrier island) between 2014 and 2016, stable isotopes in the liver, heart, and muscle, which represent different time scales, were analyzed to determine residence through δ¹³C values and niche width and trophic coexistence through δ¹⁵N values. Differences between sexes (δ¹³C liver: p = 0.009; heart: p = 0.01) and age classes (δ¹⁵N muscle: p = 0.02) were found, which indicated trophic sexual segregation and changes in resource use during growth, respectively. The lack of significant differences in δ¹³C values indicated isotopic equilibrium between the tissues, indicating the possible permanent residence of 12 dolphins in Terminos Lagoon as a coastal ecotype (− 16‰) and a second group (five dolphins) as an oceanic ecotype (− 18‰). In conclusion, most dolphins stranded in the Terminos Lagoon are potential permanent residents of this habitat, with evidence of resource partitioning as a coexistence strategy.