The Galapagos fur seal, Arctocephalus galapagoensis, is a marine mammal found exclusively within the Galapagos Islands. As the smallest eared seal, it occupies a specific niche in the archipelago’s marine environment. Their survival relies on a specialized diet and foraging behaviors, adapted to local oceanographic conditions. Understanding their feeding habits provides insight into their role in the Galapagos food web.
Main Prey Species
The Galapagos fur seal’s diet primarily consists of small fish and cephalopods. They predominantly consume deep-sea organisms like lanternfish (myctophids) and deep-sea smelts (bathylagids). Squid and octopus are also regular parts of their diet.
Galapagos fur seals are opportunistic feeders, adjusting their prey choices based on availability. While fish and cephalopods form the bulk of their intake, they may also consume crustaceans. This adaptability allows them to utilize different food sources present in their marine environment.
Hunting Strategies
Galapagos fur seals primarily forage at night when their prey is more accessible. This nocturnal behavior allows them to target fish and cephalopods that migrate closer to the ocean surface after dusk. Their large eyes are adapted for low-light conditions, aiding in locating prey in the darkness.
These seals are capable divers, typically reaching depths between 10 and 50 meters during their foraging trips. They have been observed making deeper dives, with some females recorded descending to a maximum depth of 169 meters.
Foraging trips can be lengthy, averaging around 16 hours, and their duration varies significantly with lunar cycles. Trips during a new moon, when light is minimal, may extend to 50-70 hours, while full moon periods see shorter trips of 10-20 hours, potentially due to increased visibility to predators and deeper prey migration. Their sensitive whiskers, or vibrissae, also assist in detecting prey within murky waters.
Dietary Adaptations and Influences
The diet of Galapagos fur seals is shaped by environmental conditions, particularly major oceanographic events. El Niño events, characterized by warmer ocean temperatures, can impact the availability of their primary prey by reducing marine productivity. During such periods, food becomes scarce, which can lead to increased competition for resources and higher mortality rates, especially among young pups.
Despite these challenges, Galapagos fur seals demonstrate adaptability in their feeding habits. Their ability to shift their diet in response to changes in prey abundance allows them to cope with environmental fluctuations. Physiologically, they possess a thinner blubber layer compared to other fur seal species, which helps them regulate body temperature in the warm tropical waters of the Galapagos. Their circulatory system is also adapted for efficient oxygen transport, supporting their deep-diving capabilities and the energetic demands of continuous foraging. The long lactation period of fur seals, extending up to two or three years, is also considered an adaptation to ensure pup survival during times of food scarcity.