Vertical habitat niches and individual specialization contribute to coexistence of a shark community at an oceanic pinnacle

Coexistence may be facilitated via resource partitioning along spatial, dietary or temporal axes. Within marine communities, spatial partitioning may include a vertical component based on the depths animals select. Roca Partida, is a small (100 m length) isolated oceanic pinnacle within the Revillagigedo Archipelago, Mexico. Despite its small size, several shark species reside there, and it is unclear how so many predators coexist in such a small habitat. We used acoustic and satellite telemetry and niche modelling to quantify vertical and temporal partitioning of four species: Galapagos ( Carcharhinus galapagensis ), silky ( Carcharhinus falciformis ), silvertip ( Carcharhinus albimarginatus ), and whitetip reef sharks ( Triaenodon obesus ). Galapagos and silky sharks had narrow vertical niches, with highest probability of occurrence at 0–30 m, while silvertip and whitetip reef sharks showed broader vertical niches, with highest probabilities of occurrence at 40–50 m. However, there was also significant individual variability within species, with individuals routinely using the same and sometimes non-overlapping depths with conspecifics. There was significant overlap in depth use between silky and whitetip reef sharks, while silvertip sharks were segregated from the other species. Our results match general predictions from game theory models of habitat selection, with exploitation and/or interference competition driving habitat selection, although we could not confirm the drivers of swimming depths. We also show that even for species with a broad vertical niche at the population level, there may be a narrow range of swimming depths specialization at the individual level. Future work should determine how diets compare between and within species and how this may relate to the distribution of prey at the pinnacle.