7 research outputs found
Species-specific population trends detected for penguins, gulls and cormorants over 20 years in sub-Antarctic Fuegian Archipelago
Understanding the dynamics and causes of population trends are essential for seabird conservation. Long-term studies of seabirds at high-latitude (Antarctic, sub-Antarctic and Arctic) regions have shown contrasting species-specific trends in population size in response to climate change and anthropogenic pressures. We have studied for the last 20 years (1992?2012) the population trends of seven seabird species that breed in the Beagle Channel, south-eastern Tierra del Fuego and at Staten Island, a sub-Antarctic region in southern Argentina. The numbers of Magellanic and Gentoo Penguins increased significantly since 1992 (by[15 % year-1). In comparison, the populations of Imperial Cormorants, Dolphin Gulls and Kelp Gulls increased at slower rates ( % year-1), while the Rock Cormorant population even decreased by 1.3 % year-1. At Staten Island, the numbers of Rockhopper Penguins decreased by 24 % between the censuses of 1998 and 2010, whereas the population of Magellanic Penguins increased by 227 % during the same period. Over the study period, air and sea-surface temperatures remained stable in our study area, suggesting that the detected population changes are not driven by the climate. This finding contrasts with the detected links between increasing temperature trends and seabird population changes reported from Antarctic and Arctic regions. The level of tourism and size of the permanent human population has increased in the Beagle Channel area during the last 20 years and could be responsible for the increase of gull populations. The seabird species that received the highest number of visitors (Imperial Cormorants and penguin species) seem to be adapted or at least indifferent to pressures exerted by tourism, as their populations increased during the study period. In addition, increasing numbers of seabirds in the area may generally be leading to higher abundances of scavenging species (e.g. gulls).Fil: Raya Rey, Andrea NĂ©lida. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro Austral de Investigaciones CientĂficas; ArgentinaFil: Rosciano, Natalia Gimena. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro Austral de Investigaciones CientĂficas; ArgentinaFil: Liljesthrom, Marcela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro Austral de Investigaciones CientĂficas; ArgentinaFil: Saenz Samaniego, Ricardo Andres. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro Austral de Investigaciones CientĂficas; ArgentinaFil: Schiavini, Adrian Carlos Miguel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro Austral de Investigaciones CientĂficas; Argentina. Wildlife Conservation Society; Estados Unido
Species-specific population trends detected for penguins, gulls and cormorants over 20Â years in sub-Antarctic Fuegian Archipelago
Environmental Niche Overlap between Common and Dusky Dolphins in North Patagonia, Argentina.
Research on the ecology of sympatric dolphins has increased worldwide in recent decades. However, many dolphin associations such as that between common dolphins (Delphinus delphis) and dusky dolphins (Lagenorhynchus obscurus) are poorly understood. The present study was conducted in the San MatĂas Gulf (SMG) ecosystem (North Patagonia, Argentina) where a high diet overlap among both species was found. The main objective of the present work was to explore the niche overlap of common and dusky dolphins in the habitat and temporal dimensions. The specific aims were (a) to evaluate the habitat use strategies of both species through a comparison of their group attributes (social composition, size and activity), and (b) to evaluate their habitat preferences and habitat overlap through Environmental Niche modeling considering two oceanographic seasons. To accomplish these aims, we used a historic database of opportunistic and systematic records collected from 1983 to 2011. Common and dusky dolphins exhibited similar patterns of group size (from less than 10 to more than 100 individuals), activity (both species use the area to feed, nurse, and copulate), and composition (adults, juveniles, and mothers with calves were observed for both species). Also, both species were observed travelling and feeding in mixed-species groups. Specific overlap indices were higher for common dolphins than for dusky dolphins, but all indices were low, suggesting that they are mainly segregated in the habitat dimension. In the case of common dolphins, the best habitats were located in the northwest of the gulf far from the coast. In the warm season they prefer areas with temperate sea surface and in the cold season they prefer areas with relatively high variability of sea surface temperature. Meanwhile, dusky dolphins prefer areas with steep slopes close to the coast in the southwestern sector of the gulf in both seasons