Galapagos Sea Lion Zalophus Wollebaeki Research Articles

Concentrations of lead in pinniped bones confirm Galapagos as a relatively unpolluted environment

Lead (Pb) is a trace element that is naturally present in arid regions but it is also released to the marine environment by anthropogenic industrial emissions. Here, we assessed Pb concentrations in bone samples of four pinniped species: the Galapagos sea lion Zalophus wollebaeki, sampled in Galapagos archipelago, the monk seal Monachus monachus from Mauritania, and the South American fur seal Arctocephalus australis and the South American sea lion Otaria flavescens, from Uruguay, and investigate potential geographic differences. Concentrations of lead in the samples from Galapagos were lower than those detected in samples from Mauritania and Uruguay, indicating that the Galapagos archipelago is a comparatively pristine spot for this toxic element as related to the other two areas. The waters of Mauritania and Uruguay are likely affected by the inputs of lead brought by the desert dust and released by the local industry, respectively. This study supports the use of bone to assess lead concentrations in biota, as well as the use of pinnipeds as bioindicators of marine pollution.

Environment-driven changes in terrestrial habitat use and distribution of the Galapagos sea lion

Understanding habitat use patterns of marine apex predators is of paramount impor- tance for the effective design of conservation plans. Due to their amphibious life cycle, pinnipeds are one of the most vulnerable groups to habitat loss and degradation. Reducing knowledge gaps that still exist regarding temporal changes in tropical pinniped habitat use is therefore of particu- lar importance for conservation efforts. We analyzed terrestrial habitat use phenology of a tropical otariid, the Galapagos sea lion Zalophus wollebaeki. Regular land-based censuses were carried out in Wreck Bay of San Cristobal Island, Galapagos, between 2008 and 2012 to explore seasonal changes in sea lion abundance, distribution, and preferences among different habitat types. A daily cycle of haul-out patterns was observed. Animals aggregated on sandy beaches during the coldest periods of the day and were more abundant on rocky and artificial structures when air temperature was warmer. The use of artificial floating platforms as resting places by Z. wollebaeki was described for the first time and linked to environmental variability, suggesting that this may be a successful management tool for pinnipeds inhabiting low latitudes. Further, this species demonstrated seasonal distribution changes, aggregating in high densities during warm seasons and maintaining more even distributions during cold seasons. Sea surface temperature, air tem- perature, and the onset of the breeding season were the variables that most significantly influ- enced haul-out patterns of Z. wollebaeki, indicating that this species can adapt to changing envi- ronmental conditions by displaying a high degree of plasticity regarding its distribution and terrestrial microhabitat preferences.

Proximity loggers on amphibious mammals: a new method to study social relations in their terrestrial habitat

Amphibious mammal species alternate between foraging at sea and attendance on land. Due to thermoregulatory requirements, they often haul out during the night, making social interactions difficult to observe. We tested the suitability of UHF-proximity loggers for assessing social relationships among Galapagos sea lions Zalophus wollebaeki. To survive periods at sea, proximity loggers were embedded in epoxy. Automatic downloads to receiving stations rendered logger recovery unnecessary. Encounters were logged within a range of 10 m. Logs provided information about interacting individuals as well as time and duration of encounters. 'Received signal strength indicator' values correlated with distance, but were influenced by antenna angle and environmental factors. Laboratory tests and validation in the field demonstrated that the spa- tial resolution corresponded to 2 m. Data needed to be corrected, as single encounters were recorded as multiple logs and reciprocity of loggings between animals was not always achieved. Digital data correlated with observational data, but associations were 4 times more likely to be detected using proximity loggers. Data revealed that non-territorial males frequently associated for extended periods of time, especially during the night and even outside the study colony. The modified proximity logger system proves an excellent tool to determine social structure in situations where direct observation is limited.

Applying the tools of ecological immunology to conservation: a test case in the Galapagos sea lion

AbstractInfectious disease threatens biodiversity and human health on a global scale, and disease emergence may become more common as humans further encroach on habitats and modify environments. To accurately assess the risk of disease emergence in free‐ranging populations of vertebrates, we require an understanding of the dynamics of immunity in the wild. We applied techniques from the emergent discipline of ecological immunology to describe immune activity and dynamics in the endangered Galapagos sea lion Zalophus wollebaeki, which is threatened simultaneously by disease from domestic animals and fluctuations in food supply driven by unpredictable environmental variation. We compared immune activity from shortly after birth until 2 years of age between two Galapagos sea lion colonies: one heavily influenced by humans and the other on an uninhabited island, using a generalized linear model framework. Controlling for development, immune activity was higher in the human‐impacted colony, as assessed with both humoural and cellular immune components and cumulative and snapshot measures of immune activity. We discuss the possibility that sea lions in the human‐impacted colony are under greater immunostimulatory pressure than those in the comparison colony, which could have implications for individual fitness, colony stability and the risk of disease emergence. The study demonstrates the utility of a generalized and widely applicable approach to quantifying immune activity in wild vertebrates, as it highlights important aspects of the system for targeted analysis and further study.

Age, body mass and environmental variation shape the foraging ontogeny of Galapagos sea lions

Size- and age-specific physiological constraints coupled with inexperience make the transition to independent foraging in juvenile divers a crucial period with important consequences for survival, dispersal and future reproduction. Variation in environmental conditions and associ- ated changes in food availability can additionally constrain the juvenile's development to inde- pendence. Juvenile Galapagos sea lions Zalophus wollebaeki (GSL) represent an extreme exam- ple of these constraints owing to a low growth rate, seasonal variation in food abundance and unpredictable declines in food availability during El Nino events. Time−depth recorder (TDR) data and stable isotope data of δ 15 N and δ 13 C of known age juvenile GSL were analysed to inves- tigate the development of diving and foraging, and a regular year was compared with an El Nino year to determine the effect of environmental change on the foraging behaviour of juvenile and adult GSL. GSL juveniles started diving activity at 12 mo of age and showed distinct juvenile- specific diving strategies that suggest there is an ontogenetic niche shift between juvenile and adult GSL foraging. Successful independent foraging, indicated by a strong decrease in δ 15 N ratio, started considerably later (at 18 mo of age) and was further delayed in the El Nino warm season, indicating there is an even longer dependency on maternal milk during environmentally adverse conditions. Our results suggest that prolonged maternal energetic investment buffers GSL juveniles against the constraints of diving and foraging under environmentally variable conditions and is linked to the low reproductive rate of this species.

Multiple foraging strategies in a marine apex predator, the Galapagos sea lion Zalophus wollebaeki

Three fundamental foraging patterns in air-breathing marine vertebrates have been described: epipelagic, mesopelagic and benthic. Many sea lion species with access to extensive con- tinental shelves have been described as benthic foragers. Coincidently these species are considered threatened. The Galapagos sea lion Zalophus wollebaeki, a top predator in the Galapagos Islands, is also considered threatened in this ecosystem. Sea lions at the central part of the archipelago have access to a vast continental shelf. For this reason we hypothesized that sea lions within this region would dive benthically. In addition, effective protection and conservation of this species requires knowledge of their foraging patterns and habitat utilization. We investigated the diving behaviour and habitat utilization of female Z. wollebaeki of a centrally located colony situated inside the high- est density area of the population using time-depth recorders and satellite telemetry. Three distinct foraging patterns were found and described (shallow, deep and bottom divers), and individuals uti- lizing each pattern foraged in different locations. Epipelagic, mesopelagic and benthic dives were exhibited in the sea lions' diving behaviour, but these dive types were not exclusively associated with a foraging pattern. Between foraging trips females hauled out more frequently on other islands than they did on their breeding colony. The finding of 3 distinct foraging patterns that differ spatially has direct implications for management, particularly with regard to fisheries interactions. Marine pro- tected areas can be implemented in the regions described as Z. wollebaeki foraging areas. Z. wolle- baeki's wide foraging range coupled with their use of multiple haul-out sites should be considered in future studies when determining foraging trip lengths and habitat utilization since presence/absence from the colony does not reflect foraging trip length.

Multiple foraging strategies in a marine apex predator, the Galapagos Sea Lion

Three fundamental foraging patterns in air-breathing marine vertebrates have been described: epipelagic, mesopelagic and benthic. Many sea lion species with access to extensive continental shelves have been described as benthic foragers. Coincidently these species are considered threatened. The Galapagos sea lion Zalophus wollebaeki, a top predator in the Galapagos Islands, is also considered threatened in this ecosystem. Sea lions at the central part of the archipelago have access to a vast continental shelf. For this reason we hypothesized that sea lions within this region would dive benthically. In addition, effective protection and conservation of this species requires knowledge of their foraging patterns and habitat utilization. We investigated the diving behaviour and habitat utilization of female Z. wollebaeki of a centrally located colony situated inside the highest density area of the population using time-depth recorders and satellite telemetry. Three distinct foraging patterns were found and described (shallow, deep and bottom divers), and individuals utilizing each pattern foraged in different locations. Epipelagic, mesopelagic and benthic dives were exhibited in the sea lions’ diving behaviour, but these dive types were not exclusively associated with a foraging pattern. Between foraging trips females hauled out more frequently on other islands than they did on their breeding colony. The finding of 3 distinct foraging patterns that differ spatially has direct implications for management, particularly with regard to fisheries interactions. Marine protected areas can be implemented in the regions described as Z. wollebaeki foraging areas. Z. wollebaeki’s wide foraging range coupled with their use of multiple haul-out sites should be considered in future studies when determining foraging trip lengths and habitat utilization since presence/absence from the colony does not reflect foraging trip length