Spatial variation in the foraging behaviour of the Galapagos sea lions (Zalophus wollebaeki) assessed using scat collections and stable isotope analysis

Abstract

This study focuses on the comparative analysis of variables related to the trophic niche plasticity in the Galapagos sea lion (Zalophus wollebaeki). There is great concern regarding the future of this species, so study of the diet and the way these animals obtain their food is useful to understand and predict their survival possibilities in the long term. The combined use of scat analysis and stable isotopes helps to determine foraging habits of this species in greater detail. The objective of the study was to assess the feeding habits of Z. wollebaeki and its space -time variation. The scat analysis (n ¼ 200) gave as a result space -time changes in the foraging strategies of this species. The isotopic values (n ¼ 80) showed differences in relation to foraging grounds (d 13 C: P ¼ 0.001), but also suggested an apparent stability in the trophic level of their diet (d 15 N: P ¼ 0.084). These results constitute a relevant finding in the evolutionary behaviour of the species, showing that Z. wollebaeki has developed a high degree of plasticity in its foraging habits that may improve its survival in a highly demanding ecosystem in terms of limited and fluctuating resources.

Population Abundance of the Endangered Galapagos Sea Lion Zalophus wollebaeki in the Southeastern Galapagos Archipelago

“…The marine habitat characteristics and the environmental conditions, which differ in each region of the Galapagos Archipelago [36], influence the habitat use of the GSL [8,15–17] and determine the population trend of its rookeries; thus, similar population trends were expected among spatially close rookeries in the same region. However, we found different abundance patterns among rookeries in the SER, suggesting that the population trend of a single rookery should not be considered representative of the trend in the entire region.…”

“…that alternate in frequency and abundance between the seasons [8,46]. This flexibility in the foraging behavior of the GSL has enabled it to adapt to the changing conditions of the Galapagos ecosystem and may thereby improve its survival [15]. …”

Competition influence in the segregation of the trophic niche of otariids: a case study using isotopic bayesian mixing models in Galapagos pinnipeds

“…However, satellite telemetry studies suggest the presence of two feeding strategies (pelagic and benthic), which could expand the trophic niche of this species given the region's environmental variability and the competition with other predators . This type of behavior has been related to a strategy by Z. wollebaeki to avoid competition with A. galapagoensis , primarily during the warmest months of the year when there is less prey available …”

“…The feeding habits of the Galapagos pinnipeds have been moderately studied using mainly scat analysis . However, this technique incurs intrinsic temporal biases since it provides a single snapshot of the diet of each individual before sampling, which necessitates the use of complementary techniques …”

Marine mammal research: its relationship to other scientific disciplines and to wider society

“…Using scats and stable isotope analysis, Páez-Rosas & Aurioles- Gamboa (2014) found that despite stability in trophic level, the diet of Galapagos sea lions, Zalophus californianus wollebaeki, was variable in space and time, which likely helps the species survive in an ecosystem with limited and fluctuating resources.…”