Northernmost record of dusky dolphin Lagenorhynchus obscurus in coastal waters off northern Peru (4°S)

Dusky dolphin Lagenorhynchus obscurus is distributed primarily in cool coastal waters at several continental margins and island borders in the Southern Hemisphere. Off Peru, the northernmost record of this species has been in front of the coast of Salaverry (ca., 6°S). In this paper, we report for the first-time a pod of dusky dolphin at the coast of Los Órganos (4°9.517’S; 81°11.958’W) northern Peru, thus extending the potential distributional range ca., 350 km towards the equator. A group of between 10 to 20 adult individuals was sighted on 17 October 2017, during a whale-watching excursion. Digital photographs and film allowed us to confirm the species based on body morphology and coloration. The sighted group was moving around the area without heading to a given direction. This record constitutes the northernmost record of dusky dolphin in Peru and arguably in the Southern Hemisphere.

Unravelling the function of dolphin leaps using the dusky dolphin (Lagenorhynchus obscurus) as a model species

The prevalence of leaping across delphinids indicates it has an adaptive benefit. I examined leaping behaviour in dusky dolphins (Lagenorhynchus obscurus) according to signalling, social facilitation, and prey capture hypotheses. I quantified the effect of leaping on group behaviour and fission-fusion and the behavioural context of leaping. I observed dolphins in Admiralty Bay, New Zealand during 171 focal follows totalling 157 h. Data were analysed using generalized estimating equations. Clean leaping had a positive effect on party fission () and foraging behaviour (). Coordinated leaping caused a short-term wane in foraging behaviour () and had a positive effect on party fusion (). Noisy leaping had a negative effect on perpetuating resting and traveling cessation (both ). The signalling hypothesis was the most strongly supported. The social facilitation and prey capture hypotheses were moderately supported. Leaping may provide adaptive benefits such as reduced scramble competition, increased foraging efficiency, and social bonding.

Feeding ecology of dusky dolphins Lagenorhynchus obscurus : evidence from stable isotopes

The dusky dolphin Lagenorhynchus obscurus occurs in the Southern Hemisphere, where it is restricted to coastal temperate areas. This study aimed to characterize the feeding ecology of dusky dolphins inhabiting northern and central Patagonia by using δ 13 C and δ 15 N stable isotope ratios in skin samples. We searched for evidence of geographical and seasonal variation in diet and we explored dietary differences between sexes. Significant differences in the stable isotope ratios of dusky dolphins were found among the 4 gulfs under study. Skin samples from Golfo San Matías and Golfo San Jorge were 13 C-enriched and 15 N-depleted compared to those from Golfo Nuevo and Golfo San José. There was no seasonality in the diet at Golfo Nuevo, and no differences in the diet between sexes in any gulf. Furthermore, Bayesian ellipses of males and females were similar in size and the overlap was mostly symmetrical in Golfo San José and Golfo San Jorge, while in the Golfo San Matías and Golfo Nuevo, females had wider ranges of δ 15 N, suggesting the exploitation of a wider trophic niche. Finally, pelagic fishes and demersal pelagic squids were identified as the main prey for this species of dolphin, although the proportion of each prey varied regionally. El delfín oscuro Lagenorhynchus obscurus se distribuye ampliamente en el Hemisferio Sur, donde prefiere áreas templadas costeras. Este estudio tuvo como objetivo caracterizar la ecología trófica de delfines oscuros que habitan en el norte y centro de la Patagonia mediante el uso de isótopos estables de δ 13 C y δ 15 N en muestras de piel. Específicamente, buscamos evidencia de variación geográfica y estacional en la dieta de los delfines y exploramos la diferencia de dieta entre sexos. Se encontraron diferencias significativas en los valores de isótopos estables de los delfines entre los cuatro golfos bajo estudio. Las muestras de piel de Golfo San Matías y Golfo San Jorge se encuentran enriquecidas en 13 C y deprimidas en 15 N en comparación con las muestras del Golfo Nuevo y Golfo San José. No hubo estacionalidad en la dieta en el Golfo Nuevo, y no hay diferencias en la dieta entre sexos en ningún golfo. Además, las elipses bayesianas de machos y hembras fueron similares en tamaño y la superposición fue mayormente simétrica en el Golfo San José y el Golfo San Jorge, mientras que en el Golfo San Matías y el Golfo Nuevo, las hembras tienen rangos más amplios de δ 15 N, lo que sugiere la explotación de un nicho trófico más amplio. Por último, los peces pelágicos y los calamares demersales pelágicos fueron identificados como la presa principal de esta especie de delfín, aunque la contribución de cada presa varió regionalmente.