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Currently, the Galapagos sea lion (GSL, Zalophus wollebaeki ) and Galapagos fur seal (GFS, Arctocephalus galapagoensis ) are among the most important endemic species for conservation in the Galapagos Archipelago. Both are classified as “Endangered” since their populations have undergone drastic declines over the last several decades. In this study we estimated the abundance of both otariids, and their population trends based using counts conducted between 2014 and 2018 in all their rookeries, and we analyzed the influence of environmental variability on pup production. The GSL population size in 2018 in the archipelago was estimated to be between 17,000 to 24,000 individuals and has increased at an average annual rate of 1% over the last five years after applying correction factors. The highest number of GSL counted in the archipelago was in 2014 followed by a population decline of 23.8% in 2015 that was associated with the El Niño event that occurred during that year. Following this event, the population increased mainly in the northern, central and southeastern rookeries. The GSL pup abundance showed a decreasing trend with the increase in intensity of the El Niño. The GFS population in 2018 was counted in 3,093 individuals and has increased at an annual rate of 3% from 2014 to 2018. A high number of GFS counted in 2014 was followed by a population decrease of 38% in 2015, mainly in the western rookeries. There was interannual population fluctuations and different growth trends among regions of the archipelago. GSL and GFS pup abundance has a strong decreasing tendency with the increase in the subthermocline temperature (ST) and the El Niño 1 + 2 index. Our results provide evidence that both species are highly vulnerable to periodic oceanographic-atmospheric events in the Galapagos Archipelago which impact prey abundance and the flow of energy in the unique Galapagos ecosystem.

The trophic behavior of marine predators varies according to the level of competition to which they are exposed. In general, populations that inhabit lower productivity systems face a strong intraspecific competition, which contributes to the development of different foraging strategies to maximize nutritional efficiency. Given the high trophic flexibility of Zalophus wollebaeki, this species is considered appropriate for the analysis of such behavior. Furthermore, this trophic flexibility has allowed them to persist in a seemingly marginal ecosystem. In this study, we used a comparative analysis of variables (diet and dive behavior) related to Z. wollebaeki trophic niche plasticity to better understand their foraging ecology, using techniques such scat analysis, satellite telemetry and complementarily an isotopic analysis. Scat analysis revealed intra-population variation in their diet, represented by prey from different environments (epipelagic and benthic). These results are supported by the animals' locations at sea and diving profiles. Global Positioning System (GPS) and time-depth recorder (TDR) records showed the existence of two groups, with differing feeding areas and diving behavior. Also the δ15N values showed differences in the trophic level at which the species fed. These results constitute a relevant finding in the evolutionary behavior of the species, showing that Z. wollebaeki has developed a high degree of foraging flexibility, thus increasing its survival rate in an ecosystem that is highly demanding in terms of resource availability.

There is great concern regarding the population status of the endangered Galapagos sea lion (GSL) because it has drastically decreased over the last 30 years. We determined the population size and growth trend of the GSL in the Galapagos southeastern region (SER) at three population levels based on the available census data: 1) SER (2011-2015), including 13 rookeries on the four islands San Cristóbal (SC), Española, Floreana, and Santa Fe, comprising 58% of the archipelago's population; 2) SC (2011-2015), including five rookeries, comprising 52% of the SER population; and 3) El Malecón (2005-2015), the largest rookery on SC and in the SER (43% of the population on SC and 22% in the SER). We also analyzed the influence of environmental variability on pup abundance in these rookeries. The current GSL population size in the SER, after applying correction factors to the counts, is estimated at approximately 2300-4100 individuals and has declined at an average annual rate (ʎ) of 8.7% over the last five years. A similar trend was determined for SC but at ʎ = 1.4% during the same period. For El Malecón, a count-based population viability analysis using a diffusion approximation approach showed that the population increased from 2005 to 2015 at ʎ = 2%. The interannual variability in pup abundance was associated with anomalies in sea surface temperature linked to oceanographic-atmospheric events, which impact the abundance and availability of prey, and ultimately may determine the population's reproductive success. Since rookeries in the SER had different population trends, management actions should be implemented based on their specific conditions, giving priority to rookeries such as El Malecón, which, despite showing a slightly increasing population trend, still faces a high risk of extinction due to anthropogenic disturbances and environmental variability that may affect its growth and survival.

We report a case of severe conjunctivitis in a traveler infected with a Philophthalmus lacrymosus eye fluke, probably acquired on the Galápagos Islands in Ecuador. This zoonotic parasite is endemic in Brazil and Venezuela, where it has been reported in birds and capybaras.

Changes in life-history requirements drive trophic variations, particularly in large marine predators. The life history of many shark species is still poorly known and understanding their dietary ontogeny is a challenging task, especially for highly migratory species. Stable isotope analysis has proven as a useful method for examining the foraging strategies of sharks and other marine predators. We assessed the foraging strategies and ontogenetic changes of scalloped hammerhead sharks, Sphyrna lewini , at Galapagos Marine Reserve (GMR), by analysing δ 13 C and δ 15 N signatures in different maturity stages. Our isotopic results suggest ontogenetic shifts in resource use between sub-adult and adult stages, but not between adult and juvenile stages. Carbon isotopic signatures found in the juvenile stage were enriched in contrast to sub-adults (~0.73‰) suggesting a combination of the maternal input and the use of coastal resources around the Galapagos Islands. Adult female sharks also showed enrichment in δ 13 C (~0.53‰) in comparison to sub-adult stages that suggest feeding in high primary productivity areas, such as the GMR. This study improves the understanding of the trophic ecology and ontogenetic changes of a highly migratory shark that moves across the protected and unprotected waters of the Eastern Tropical Pacific.

Introduced rodents are responsible for ecosystem changes in islands around the world. In the Galapagos archipelago, their effects on the native flora and fauna are adverse, including the extinction of endemic rodents in some islands and the reduction in the reproductive success of the Galapagos petrel (Pterodroma phaeopygia) in its nesting zones. Understanding the feeding behavior of introduced rodents and their trophic interactions with native and non-native species on islands, can assist in the design of management strategies and conservation plans of invasive and endemic species respectively. Four petrel nesting colonies were monitored during June 2013 on San Cristóbal Island (El Plátano, El Junco, San Joaquín, and La Comuna). The feeding habits of black rats were evaluated by analyzing stomach contents and stable isotopes in hair. Three species of introduced rodents were captured. R. rattus was the most abundant at all sites (n=43, capture success (CS) = 55.8%), followed by the house mouse, Mus musculus (n = 17, CS = 37.8%), and the Norwegian rat, R. norvegicus (n = 4, CS = 4.5%), captured only at La Comuna. The omnivorous black rat ate mostly plants (98%) and arthropods (2%). Intact seeds of Miconia robinsoniana were the main food at all sites (relative abundance=72.1%, present in 95% of the analyzed stomachs), showing the black rats' possible role in the archipelago as endemic seed dispersers. There was no evidence of petrel's intake; however, its possible consumption is not discarded at all. The δ15N and δ13C analysis corroborated the primarily herbivorous diet of black rats. The isotopic signatures of the three rodent species reflect the inter- and intra-specific differential use of food resources. Black rat showed a wider diet in La Comuna, which was related to a lower availability of its primary prey and its ability to adapt to the available resources in its habitat.

Tropical ecosystems are challenging for pinnipeds due to fluctuating food availability. According to previous research, the Galapagos sea lion (GSL, Zalophus wollebaeki) adopts trophic flexibility to face such conditions. However, this hypothesis comes from studies using traditional methods (hard‐parts analysis of scat and isotopic analysis from tissue). We studied the diet of five rookeries in the southeastern Galapagos bioregion (which harbors the highest GSL density), via DNA‐metabarcoding of scat samples. The DNA‐metabarcoding approach may identify consumed prey with a higher taxonomic resolution than isotopic analysis, while not depending on hard‐parts remaining through digestion. Our study included five different rookeries to look for evidence of trophic flexibility at the bioregional level. We detected 98 prey OTUs (124 scats), mostly assigned to bony‐fish taxa; we identified novel prey items, including a shark, rays, and several deep‐sea fish. Our data supported the trophic flexibility of GSL throughout the studied bioregion since different individuals from the same rookery consumed prey coming from different habitats and trophic levels. Significant diet differentiations were found among rookeries, particularly between Punta Pitt and Santa Fe. Punta Pitt rookery, with a more pronounced bathymetry and lower productivity, was distinguished by a high trophic level and consumption of a high proportion of deep‐sea prey; meanwhile, Santa Fe, located in more productive, shallow waters over the shelf, consumed a high proportion of epipelagic planktivorous fish. Geographic location and heterogeneous bathymetry of El Malecon, Española, and Floreana rookeries would allow the animals therein to access both, epipelagic prey over the shelf, and deep‐sea prey out of the shelf; this would lead to a higher prey richness and diet variability there. These findings provide evidence of GSL adopting a trophic flexibility to tune their diets to different ecological contexts. This strategy would be crucial for this endangered species to overcome the challenges faced in a habitat with fluctuating foraging conditions. Trophic flexibility is paramount for Galapagos sea lions to thrive in a marginal, tropical habitat. We got solid evidence of trophic flexibility at five different sea lion rookeries and at a broader, bioregional level. This evidence includes the use of prey originating from different habitats and trophic levels by sea lions, a richer diet in more populated rookeries to prevent competition, and the coupling of the sea lion diets with the local bathymetric and oceanographic conditions around each rookery.

Coastal habitats are essential for ecological processes and provide important ecosystem services. The Galapagos archipelago has a wide diversity of ichthyofauna which preservation guarantees the functioning of the marine ecosystem. In this study, we used ecological and taxonomic indices as well as multivariate analysis to identify spatiotemporal changes in fish community structure in coastal habitats of San Cristóbal Island in the southeastern Galapagos archipelago. We analyzed how the patterns of variability were related to the abiotic conditions (substrate, sea temperature and depth) of each habitat. Nine sites affected by anthropogenic influence (fishing and tourism) representing different habitats/substrates were sampled. Underwater surveys were conducted during the warm and cold seasons in 2010 and 2011 at transects that varied in depth according to site. Artificial habitat, followed by coral and rocky habitats, had the highest diversity, evenness, and taxonomic distinctness, while mangrove habitats had the lowest values. This was related to the habitat complexity and possible anthropogenic influences. While the diversity patterns were more strongly related to the type of substrate, followed by the combination of substrate and depth, and the sea temperature had less influence. These findings were related to the ecological traits of the fish communities and their mobility between habitats. Temporal changes in fish community diversity and composition were not detected at all sites, suggesting that these species have high fidelity to their habitats and a high environmental tolerance that allows them to persist in their habitats despite strong changes in sea temperature on the Galapagos archipelago.

Aim Environmental heterogeneity shapes species diversity by creating ecological niches (habitat heterogeneity hypothesis). Yet its role in driving behavioural diversity within species remains only partially understood. Behavioural diversity enhances a population's ability to exploit ecological niches and adapt to environmental change, making it critical to understand how behaviour is shaped by environmental factors. Here we test whether spatial and temporal heterogeneity predict behavioural diversity at population and individual levels across species and environments. Location Global. Methods We synthesised biologging data from five species of sea lions (15 colonies, 370 individuals, 927,000 dives) to test the relationship between population‐level behavioural variation and individual specialisation/flexibility metrics with bathymetric roughness, mean chlorophyll and interannual chlorophyll variability utilising GLMMs. Results We provide large‐scale, multi‐species evidence that environmental heterogeneity drives behavioural diversity. We show that populations foraging in structurally complex habitats and with greater resource variability exhibited more diverse dive and foraging behaviour, demonstrating that environmental heterogeneity, both in space and time, is associated with higher behavioural diversity. While habitat complexity fostered population‐level variation, environments with low productivity favoured specialisation on the individual level, suggesting a shift from generalist to specialist strategies under resource limitation. Main Conclusions The consistent pattern between environmental heterogeneity and population‐level behavioural diversity across species and environments suggests, in combination with observations from previous studies, a fundamental principle extending beyond species and habitat borders. We therefore suggest broadening the habitat heterogeneity hypothesis from species richness to within‐species variation. Our findings underscore two important conservation considerations: (1) conserving habitat complexity to help maintain behavioural diversity; and (2) prioritising protection for populations in low‐heterogeneity environments, where reduced behavioural flexibility may increase vulnerability to environmental change.

Sharks are top predators across ocean food webs and have a major ecological role in marine ecosystems. Investigating the trophic ecology of this group of species is thus essential to understand ecosystem functioning and inform specific management actions aimed at shark conservation. The Galapagos Islands represent one of the last ocean wildernesses, where populations of sharks and other top marine predators come close to a pristine status. Here we provide the first study on the trophic ecology of the tiger shark (Galeocerdo cuvier) within the Galapagos Marine Reserve (GMR), using a combination of stable isotope analysis, satellite tracking, and passive acoustic telemetry to investigate ontogenetic and spatial variations at two regions. The mean estimated δ13C and δ15N at Isabela island (western region) were -13.9 ± 0.5‰ and 13.7 ± 0.7‰; and for Santa Cruz island (central region) were -13.8 ± 0.3‰ and 13.4 ± 0.7‰, respectively. Green sea turtles (Chelonia mydas) were the main prey item for large tiger sharks (>280 cm TL), while smaller sharks mainly fed on squid and pelagic fish. Tiger sharks exhibited a high degree of philopatry around green sea-turtle nesting areas, with the majority of sharks detected around green sea-turtle nesting areas for at least 10 months after their capture date, and some individuals were even present during the entire three-year study period. Although we did not report statistically significant differences between the two regions, isotopic and electronic tagging data suggest that tiger sharks in the Galapagos could be segregated into specific populations separated by geographical scales of <100 km. The high productivity of the archipelago, along with the protection from industrial fishing granted by the GMR, result in abundant and predictable sources of prey. This high food abundance, combined with the presence of suitable habitats throughout the tiger shark life cycle, might result in a reduction of migratory behaviours when compared to movement patterns of tiger sharks in other ocean basins. Additional studies using genetic tools could provide further evidence on the presence of separate management units, as it has been recently revealed for other shark species inhabiting the GMR.