Maritza Sepúlveda

Distribution and abundance of the South American sea lion Otaria flavescens (Carnivora: Otariidae) along the central coast off Chile

Se estimo la distribucion y la abundancia poblacional del lobo marino comun Otaria flavescens en la costa de Chile central durante los meses de enero y febrero de 2007. Adicionalmente, se analizaron los cambios en la abundancia de esta especie durante el periodo 1970-2007. Los censos poblacionales se basaron en fotografias tomadas desde embarcaciones menores o desde avionetas. Se contabilizaron un total de 16301 lobos marinos (IC = 16209-16375) en 33 colonias (6 reproductivas y 27 no reproductivas). Despues de corregir por la proporcion de animales en el agua y por crias no registradas al momento del censo, se estimo una abundancia promedio de 18179 (95 % CI = 17777-18851) lobos marinos en el area de estudio. El analisis de tendencia poblacional presento que desde 1970 a 1985 la abundancia-lobo marino com-mostro una tendencia positiva de aproximadamente 2.1 % ano-1. Sin embargo, entre 1985 a 1997, y entre 1997 a 2007, el numero de lobos marinos muestra una tendencia estable o ligeramente negativa de 0.4 ± 0.1 % ano-1 y 0.5 ± 0.1 % ano-1, respectivamente. Se sugiere que la sobreexplotacion y la declinacion de las principales pesquerias en la zona central de Chife podria haber impactado negativamente la distribucion y abundancia del lobo marino comun en el area de estudio.

Fin Whales (Balaenoptera physalus) Feeding on Euphausia mucronata in Nearshore Waters off North-Central Chile

This paper reports the presence and feeding activity of fin whales (Balaenoptera physalus) during the austral summers of 2004 and 2005 in coastal waters near the Reserva Nacional Pinguino de Humboldt, north of Chile. The main prey item of the species was identified as the euphausiid Euphausia mucronata. The presence of B. physalus is associated with a high concentration of potential prey probably produced by an upwelling system that is frequently detected slightly south of the study area during summer. This information is a contribution to the knowledge of distribution, feeding behavior, and diet of B. physalus. Additionally, it constitutes the first record of a direct observation of feeding activity of B. physalus along the Chilean coast.

Circaritmos de actividad diarios y anuales en el lobo marino común Otaria flavescens (Carnivora: Otariidae) en la zona central de Chile

En otaridos se han estudiado la presencia de circaritmos de actividad sobre la base de cambios en las densidades poblacionales en las loberas. En este trabajo, se estudiaron los ritmos circadiano (24 h) y circanual (1 ano) del lobo marino comun Otaria flavescens en las loberas de Cochoa y Punta Curaumilla en Chile Central. El ritmo circadiano fue estudiado en ambas loberas. En cada una de ellas se realizaron censos cada 45 min durante 3 dias de observacion continuos (72 h). Los resultados demuestran que se produce un aumento del numero de animales en tierra en horarios diurnos y una disminucion en los nocturnos. Dichas fluctuaciones estan asociadas a un ciclo de 24 h, y demuestran la existencia de un ritmo circadiano en estas loberas. El ritmo circanual fue estudiado en la lobera de Cochoa. Para ello se realizaron 145 observaciones durante 3 anos consecutivos (1995-1998). Los resultados muestran un aumento de la poblacion en los meses de otono a primavera, y una disminucion brusca en el verano. Estas fluctuaciones se asocian a un ciclo de un ano, y demuestran la existencia de un ritmo circanual en esta especie.

Regional variability in diving physiology and behavior in a widely distributed air-breathing marine predator, the South American sea lion (Otaria byronia).

ABSTRACT Our understanding of how air-breathing marine predators cope with environmental variability is limited by our inadequate knowledge of their ecological and physiological parameters. Because of their wide distribution along both coasts of the sub-continent, South American sea lions (Otaria byronia) provide a valuable opportunity to study the behavioral and physiological plasticity of a marine predator in different environments. We measured the oxygen stores and diving behavior of South American sea lions throughout most of its range, allowing us to demonstrate that diving ability and behavior vary across its range. We found no significant differences in mass-specific blood volumes of sea lions among field sites and a negative relationship between mass-specific oxygen storage and size, which suggests that exposure to different habitats and geographical locations better explains oxygen storage capacities and diving capability in South American sea lions than body size alone. The largest animals in our study (individuals from Uruguay) were the shallowest and shortest duration divers, and had the lowest mass-specific total body oxygen stores, while the deepest and longest duration divers (individuals from southern Chile) had significantly larger mass-specific oxygen stores, despite being much smaller animals. Our study suggests that the physiology of air-breathing diving predators is not fixed, but that it can be adjusted, to a certain extent, depending on the ecological setting and or habitat. These adjustments can be thought of as a ‘training effect’: as the animal continues to push its physiological capacity through greater hypoxic exposure, its breath-holding capacity increases. Summary: Regional variation in diving ability and behavior of the South American sea lion suggests that exposure to different habitats and geographical locations better explains oxygen storage capacities and diving capability than body size alone.

Using Satellite Tracking and Isotopic Information to Characterize the Impact of South American Sea Lions on Salmonid Aquaculture in Southern Chile.

Apex marine predators alter their foraging behavior in response to spatial and/or seasonal changes in natural prey distribution and abundance. However, few studies have identified the impacts of aquaculture that represents a spatially and temporally predictable and abundant resource on their foraging behavior. Using satellite telemetry and stable isotope analysis we examined the degree of spatial overlap between the South American sea lion (SASL) and salmon farms, and quantify the amount of native prey versus farmed salmonids in SASL diets. We instrumented eight SASL individuals with SRDL-GPS tags. Vibrissae, hair and skin samples were collected for δ13C and δ15N analyses from five of the tagged individuals and from four males captured in a haul-out located adjacent to salmon farms. Tracking results showed that almost all the foraging areas of SASL are within close proximity to salmon farms. The most important prey for the individuals analyzed was farmed salmonids, with an estimated median (±SD) contribution of 19.7 ± 13.5‰ and 15.3 ± 9.6‰ for hair and skin, respectively. Using vibrissae as a temporal record of diet for each individual, we observed a remarkable switch in diet composition in two SASL, from farmed salmonids to pelagic fishes, which coincided with the decrease of salmon production due to the infectious salmon anemia virus that affected salmon farms in Chile at the end of 2008. Our study demonstrates the usefulness of integrating stable isotope derived dietary data with movement patterns to characterize the impacts of a non-native prey on the foraging ecology of an apex marine predator, providing important applied implications in situations where interactions between aquaculture and wildlife are common.

Diet plasticity of the South American sea lion in Chile: stable isotope evidence

Diet studies of the South American sea lion (SASL) in Chile suggest that this species is an opportun istic and generalist predator whose diet varies depending on the distribution of prey species and spatial and temporal variations in the abundance of these dams. However, these studies have been sporadic, geographically limited and based on stomach content analysis, which does not allow an integral analysis of the composition of the diet of this species and its potential spatial and temporal variability. In this study we analyzed the diet of the SASL in 3 geographic zones of the coast of Chile using analysis of stable isotopes  13 C and  15 N on hair and skin tissues. In the northern zone, the main prey species consumed by SASL were Isacia conceptionis (19.5%) for skin and Cilus gilberti (23.3%) for hair; in the central zone were Thyrsites atun (40.1%) for skin and Strangomera bentincki (31.1%) for hair, whereas in the southern zone the main species were pelagic fish (such as T. atun and Trachurus murphyi, 20.8%) for skin and farm-raised salmonids (20.7%) for hair analysis. These differences indicate variation in the composition of its diet. Variations between the analyzed tissues and also with previous studies suggest that this species is capable of adapting to intra- and inter-annual variations in the presence/absence of its prey.

Behavioral response of South American sea lion Otaria flavescens to tourist disturbance during the breeding season

Los pinipedos muestran una alta predictibilidad en su distribucion, tanto espacial como temporal, y tienden a congregarse en parches, lo que permite un facil acceso de turistas. Sin embargo, la presencia de dichos turistas puede generar un impacto negativo sobre los animales. El objetivo de este estudio fue evaluar, por primera vez en Chile, el efecto del ecoturismo sobre el comportamiento del lobo marino comun Otaria flavescens durante la epoca reproductiva. Registramos un total de 44 visitas de embarcaciones a la lobera reproductiva de Isla Chanaral. La mayoria de los turistas mostro una actitud de calma, seguida por moderada y perturbadora. La respuesta de los lobos marinos fue mayoritariamente de escape, seguida de inactiva y alerta. La respuesta de los lobos marinos se relaciono negativamente con la distancia de aproximacion de la embarcacion a la colonia, pero no se relaciono ni con el tiempo de permanencia de la embarcacion en la colonia ni con la conducta de los turistas. Nuestros resultados indican que el lobo marino comun es afectado negativamente por la presencia de turistas, especialmente debido al escape de los individuos desde la colonia al mar. Dichos escapes pueden generar efectos fisiologicos negativos sobre el animal, lo que puede incidir sobre su adecuacion biologica. Sugerimos que futuros estudios evaluen el comportamiento de respuesta de los lobos marinos durante la epoca reproductiva y en otros periodos del ano, ademas de analizar posibles diferencias entre clases de edad y sexo, lo que permita contar con herramientas adecuadas para el manejo del turismo sobre el lobo marino comun en Chile.

Ancient female philopatry, asymmetric male gene flow, and synchronous population expansion support the influence of climatic oscillations on the evolution of South American sea lion (Otaria flavescens)

The South American sea lion (Otaria flavescens) is widely distributed along the southern Atlantic and Pacific coasts of South America with a history of significant commercial exploitation. We aimed to evaluate the population genetic structure and the evolutionary history of South American sea lion along its distribution by analyses of mitochondrial DNA (mtDNA) and 10 nuclear microsatellites loci. We analyzed 147 sequences of mtDNA control region and genotyped 111 individuals of South American sea lion for 10 microsatellite loci, representing six populations (Peru, Northern Chile, Southern Chile, Uruguay (Brazil), Argentina and Falkland (Malvinas) Islands) and covering the entire distribution of the species. The mtDNA phylogeny shows that haplotypes from the two oceans comprise two very divergent clades as observed in previous studies, suggesting a long period (>1 million years) of low inter-oceanic female gene flow. Bayesian analysis of bi-parental genetic diversity supports significant (but less pronounced than mitochondrial) genetic structure between Pacific and Atlantic populations, although also suggested some inter-oceanic gene flow mediated by males. Higher male migration rates were found in the intra-oceanic population comparisons, supporting very high female philopatry in the species. Demographic analyses showed that populations from both oceans went through a large population expansion ~10,000 years ago, suggesting a very similar influence of historical environmental factors, such as the last glacial cycle, on both regions. Our results support the proposition that the Pacific and Atlantic populations of the South American sea lion should be considered distinct evolutionarily significant units, with at least two managements units in each ocean.

Testing Bergmann’s rule and the Rosenzweig hypothesis with craniometric studies of the South American sea lion

We tested the validity of Bergmann’s rule and Rosenzweig’s hypothesis through an analysis of the geographical variation of the skull size of Otaria flavescens along the entire distribution range of the species (except Brazil). We quantified the sizes of 606 adult South American sea lion skulls measured in seven localities of Peru, Chile, Uruguay, Argentina, and the Falkland/Malvinas Islands. Geographical and environmental variables included latitude, longitude, and monthly minimum, maximum, and mean air and ocean temperatures. We also included information on fish landings as a proxy for productivity. Males showed a positive relationship between condylobasal length (CBL) and latitude, and between CBL and the six temperature variables. By contrast, females showed a negative relationship between CBL and the same variables. Finally, female skull size showed a significant and positive correlation with fish landings, while males did not show any relationship with this variable. The body size of males conformed to Bergmann’s rule, with larger individuals found in southern localities of South America. Females followed the converse of Bergmann’s rule at the intraspecific level, but showed a positive relationship with the proxy for productivity, thus supporting Rosenzweig’s hypothesis. Differences in the factors that drive body size in females and males may be explained by their different life-history strategies. Our analyses demonstrate that latitude and temperature are not the only factors that explain spatial variation in body size: others such as food availability are also important for explaining the ecogeographical patterns found in O. flavescens.

Seasonal variation in the abundance of South American sea lions Otaria flavescens (Shaw, 1800) in Chañaral Island, Reserva Nacional Pingüino de Humboldt, Chile

Desde enero de 2007 y hasta marzo de 2008 se analizo la variacion de la abundancia del lobo marino comun Otaria flavescens en la lobera reproductiva Isla Chanaral, de acuerdo al sexo, clase de edad y estacion reproductiva. El mayor numero de lobos marinos en la lobera se registro durante el periodo reproductivo. Esta variacion se debio principalmente a la fluctuacion del numero de hembras, ya que esta clase de edad fue la mas importante en la colonia y mostro un aumento en su abundancia durante este periodo. No se registraron fluctuaciones estacionales en el numero de machos adultos, machos subadultos y juveniles. La proporcion de sexos durante la estacion reproductiva estuvo fuertemente sesgada hacia las hembras, mientras que fue cercana a 1:1 durante el resto del ano. Este estudio demuestra que la variacion en la abundancia y composicion por sexo y clase de edad del lobo marino comun en Isla Chanaral se relaciona principalmente con la actividad reproductiva.