Ecology, energy and effort: Variations in facultative opportunistic feeding of the common dolphin in the Celtic Seas ecoregion

36th annual European Cetacean Society Conference, Ponta Delgada (São Miguel Island, Azores, Portugal), 12-16 May 2025

Predators like the common dolphin forage by balancing the energy content of prey with the energy required to capture it, selecting prey based on their foraging strategy. Specialist or generalist foraging strategies in common dolphins, a species with high energetic demands, vary across regions. In the Celtic Seas ecoregion, no recent dietary data is available despite recent observations of declining body condition among stranded common dolphins and changes in prey communities over recent decades. Using conventional morphological stomach content analysis of a large stranding sample-set (n=138) collected over three decades, coupled with advanced modelling, we updated information on their foraging ecology in the region. Assessments of their dietary composition, trophic level, daily prey consumption (daily rations), and gross energy intake included explanatory variables time period, season, sex, maturity status, total body length, body condition, and cause of death. Advanced modelling approaches, including a bias-reduced multinomial model, novel to cetacean diet composition analysis, were applied to refine our understanding of these ecological patterns. In this study, common dolphins were identified as facultative generalists/opportunists, consuming prey of lower energy densities and at higher trophic levels compared to more southern European waters. The most important prey species were intermediate-energy Trisopterus spp., potentially representing a favouring trade-off for lower hunting effort. Variations in foraging ecology were observed across all variables, likely reflecting shifts in prey availability, reproductive needs, movement patterns, and physical capabilities. This study also highlighted the limitations of stomach content analysis, here representing only a small portion (18%) of daily required energy intake, underscoring the need for large sample sizes for robust dietary assessments. The findings provided vital insights into common dolphin ecology within the Celtic Seas ecoregion, delivering essential information to support future ecosystem-based management approaches

Peer reviewed