First Record of the Foraging Habits of Guadalupe Fur Seals in the Recently Formed Colony on Las Ánimas Island in the Southwestern Gulf of California, Mexico

Trophic resources are a crucial factor for the ongoing population recovery of the Guadalupe fur seal (Arctocephalus townsendi; GFS), driving individuals to explore and establish new feeding areas within the Gulf of California. This study aimed to assess the diet of GFS juveniles on Las Ánimas Island using fecal analysis (n = 46) in the spring of 2024. The trophic spectrum was evaluated using four ecological metrics: (1) the index of importance (IIMP%), (2) modified Costello graphs, (3) Levins’ Standardized Index (Bi), and (4) the trophic level estimate (TP). Diet analysis revealed 15 prey taxa, with cephalopods as the dominant group and, to a minor extent, mesopelagic and demersal fish. The most important prey was the fire squid (Pterygioteuthis hoylei; IIMP = 29.84%), followed by hooked squids (Onychoteuthis spp.; IIMP = 16.83%) and the jumbo flying squid (Dosidicus gigas; IIMP = 16.15%). The colony exhibited a mixed feeding strategy, with some individuals engaged in generalized foraging on pelagic squid. Despite a narrow trophic breadth and an estimated trophic level of 4.17, the presence of novel squid prey underscores the teuthophagous feeding habits of the GFS within the Gulf of California. The results from this study, along with other recent studies, show that this region is an alternative foraging ground for GFSs, with a high abundance of small pelagic squid, supplemented by mesopelagic fish, which potentially support the species’ dispersal and ongoing recovery.