Fraser’s dolphin in the Lesser Antilles: Distribution, Habitat Preferences and Co-occurrence Behavior

MSc internship report

The Lesser Antilles hosts a high diversity of cetacean species, which are essential top marine predators whose abundance reflects the overall health of marine ecosystems. Despite the high research interest in cetacean ecology, Fraser’s dolphin (Lagenodelphis Hosei) remains one of the least studied dolphin species, primarily due to its tropical offshore and low-density distribution. However, some Fraser’s dolphin populations particularly frequent the coastal waters of tropical oceanic islands featuring steep topography. The Lesser Antilles has been identified as one of the few places where Fraser’s dolphin is frequently observed, providing a unique opportunity to learn about this mysterious species. Using boat survey data collected all along the Lesser Antilles, we aimed to gain insights into Fraser’s dolphin distribution and habitat preferences. Consequently, we used presence-absence Generalized Additive Models to identify the environmental covariates that best explained its distribution and used them to predict habitat suitability. presence is suspected all year-around and was confirmed during our sampling period from March to October along the Lesser Antilles arc. Covariates such as chlorophyll a concentration, proximity to canyons, sea surface temperature, depth, and eastward current velocity best explained the observed distribution. An amount of 76% of Fraser’s dolphin observations co-occurred with a total of 6 other cetacean species. To understand if this pattern is unique to Fraser’s dolphin, we performed a simple statistical analysis of cetacean co-occurrences to test for its significance. Fraser's dolphin exhibited more frequent associations with other species, and these associations displayed greater strength compared to interactions involving other cetacean species. We hypothesize that the co-occurrence behavior of Fraser's dolphin is likely driven by a versatile and opportunistic foraging strategy. The presence of occasional feeding surface behaviors provides evidence that its diet in the Lesser Antilles may not be confined to mesopelagic prey species.