Environmental Niche Overlap between Common and Dusky Dolphins in North Patagonia, Argentina

Abstract

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 Matías 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.

Distribución potencial de mamíferos marinos durante el verano austral en el Golfo San Jorge, Argentina

“…Despite the low number of records used in this study, environmental variables that influence the distribution of marine mammals agreed with those found in other systematic studies focused on isolated/single species as the dusky dolphin (Garaffo 2009, Garaffo et al 2010, 2011Svendsen et al 2015), Peale's dolphin (Viddi & Lescrauwaet 2005, Viddi et al 2010, Commerson´s dolphin (Coscarella et al 2011, Garaffo et al 2011, Loizaga de Castro et al 2013) sea lions (Svendsen 2013, Baylis et al 2016 or southern elephant seals (Campagna et al 2007). For L. obscurus the most important environmental variables that affected their potential distribution were bathymetry and slope, showing a suitable habitat in shallower areas with steep slopes.…”

“…For L. obscurus the most important environmental variables that affected their potential distribution were bathymetry and slope, showing a suitable habitat in shallower areas with steep slopes. Both variables and distance to the coast, explained the distribution in other Patagonian gulfs where there was no influence of tidal fronts (Garaffo et al 2010(Garaffo et al , 2011Svendsen et al 2015). In this case, the distance to the coast was not a significant variable due to the threshold located in the south of the SJG where at large distance from the coast the depth still remains shallow.…”

“…Pearson et al (2007) demonstrated a significant predictive ability for Maxent models with as few as 5 observed localities. The model was selected for its apparent comparatively high performance in relation to other modeling methods (Elith et al 2006 for a review), it has also been used successfully to predict the distributions of marine mammals (Friedlaender et al 2011, Moura et al 2012, Bombosch et al 2014, Gomez & Cassini 2015, Svendsen et al 2015). …”

Using stable isotopes to assess whether two sympatric dolphin species share trophic resources

“…Nevertheless, the coexistence of these two species within the same community is probably favored by segregation in both the habitat dimension (Svendsen et al . ) and in the trophic resources (present study).…”

“…In this sense, short‐beaked common dolphins prefer habitats located in the northwest section of the gulf far from the coast; whereas dusky dolphins prefer areas with steep slopes close to the coast in the southwestern sector of the gulf (Svendsen et al . ).…”