RESUMO
Una comunidad residente de bufeos costeros Tursiops truncatus ha sido estudiada de manera intermitente entre 2005 y 2018 en la punta de la península de Santa Elena, Ecuador (2°11' S & 81°0.7' W). Avistamientos oportunistas y dirigidos desde la playa y abordo de un bote con motor fuera de borda se realizaron a lo largo de 40 km de costa, contabilizándose un esfuerzo de 917.2 km de seguimiento en automóvil desde tierra y 707.4 km en bote por mar. El tamaño grupal promedio fue 5.31 delfines/grupo (SD = 1.97, rango 1-10), sin cambios significativos a lo largo del estudio. Desde tierra el tamaño grupal fue subestimado en promedio en 32 %. Esta comunidad de bufeos tiene actualmente solo nueve individuos, incluyendo seis adultos, un inmaduro y dos crías, siendo la comunidad más pequeña encontrada en el golfo de Guayaquil. La tasa de encuentro varió entre 0.03 delfines/km en la parte noroeste y 0.31 delfines/km en la parte sur, donde los delfines concentran sus actividades, posiblemente porque las actividades humanas ahí son menos intensas. Los delfines se distribuyeron generalmente entre los primeros 200 m de la orilla llegando hasta 1 200 m en la parte norte donde la profundidad es menor y las actividades portuaria y turística más intensas. La velocidad de los delfines fue significativamente más alta cuando fueron seguidos desde un bote a corta distancia (5.87 km/h) que cuando fueron monitoreados desde tierra (2.9 km/h) (P < 0.01), lo cual sugiere que el seguimiento en bote tuvo un impacto sobre el movimiento de los delfines. Un análisis clúster jerárquico mostró que los delfines tienen altos índices de asociación entre ellos (promedio 0.67, rango 0.01-1.0), indicando que es una comunidad altamente cohesionada. Adicionalmente muestran un alto nivel de residencia (índice de ocurrencia promedio de 0.62). Durante el estudio se identificaron dos amenazas principales, una pesquería con redes agalleras en la parte suroeste y un intenso tráfico de botes pesqueros en la parte noroeste. La mayoría del área de estudio actualmente es parte de un área costero-marina protegida creada en 2008, lo cual ofrece una oportunidad para la recuperación de esta comunidad de delfines. Debido a su fragilidad, se recomienda a las autoridades ambientales, entre otras cosas, eliminar potenciales fuentes de amenaza para los delfines como las redes de pesca, implementar un área de exclusión para artes de pesca y tráfico de botes pesqueros de 1 km de ancho desde la orilla y limitar la velocidad de todo tipo de embarcación a 10 nudos dentro del área protegida.
A resident community of bottlenose dolphins (Tursiops truncatus) has been studied irregularly between 2005 and 2018 around the tip of the Santa Elena Peninsula, Ecuador (2°11' S & 81°0.7' W). Opportunistic sightings and systematic surveys from the beach and at sea were carried out along 40 km of coast, accounting for 917.2 km of tracking by car from land and 707.4 km of boat tracking by sea. Average group size was 5.31 dolphins/group (SD = 1.97, range 1-10), with no significant changes throughout the study period. From land, however, the group size was underestimated 32 % on the average. This small bottlenose dolphin community currently has only nine individuals, including six adults, one immature and two calves, and is the smallest community within the Gulf of Guayaquil. The encounter rate ranged between 0.03 dolphins/km in the northwestern part and 0.32 dolphins/km in the South, where dolphins concentrate their activities, possibly because human activities are less intense there. Dolphins were generally distributed in the first 200 m from the shore, reaching up to 1 200 m in the Northern shallower part and where port and tourist activities concentrate. The dolphins' speed was significantly higher when they were followed from a boat at close range (5.87 km/h) than when they were monitored from the beach (2.9 km/h) (P < 0.01), which suggests that boat tracking had an effect on dolphin´s movements. Pairwise cluster analysis showed that animals from this community show high rates of association among each other (average 0.67, range 0.01-1.0), indicating that is a highly cohesive community. Dolphins also showed high level of residence (average occurrence index = 0.62). During the study, two main threats were identified, a gillnet fishery in the Southwestern part and an intense fishing boat traffic in the Northwestern. Most of the study area is currently part of a coastal-marine protected area created in 2008, which offers an opportunity for the recovery and conservation of this dolphin community. Given its fragility, we recommend the environmental authorities to address potential threats for this dolphin community by eliminating gillnets, implementing an exclusion zone for fishing gear and boat traffic of 1 km width from the shore and limit the speed of any type of vessel to 10 knots within the reserve.
RESUMO
A ecologia do golfinho-nariz-de-garrafa (Tursiops truncatus) é pouco documentada no Brasil. O objetivo deste trabalho é fornecer dados sobre a distribuição, tamanho de grupo e comportamento de T. truncatus a partir de avistagens oportunistas realizadas nas adjacências da Ilha de Santa Catarina, sul do Brasil. Em cada observação de grupos da espécie foram registrados: localidade, data e hora, tamanho de grupo e comportamento. Foram observados 71 grupos entre 1989 e 2005, em todos os meses do ano. A espécie foi observada em toda região costeira da Ilha de Santa Catarina, utilizando uma grande variedade de hábitats. O tamanho de grupo variou entre 1 e 200 indivíduos, com uma média de aproximadamente 8 indivíduos (moda = 2). Interações com pelo menos três espécies de aves marinhas também foram observadas, além de outros comportamentos. Os dados obtidos sugerem que a espécie é comum ao longo da costa da Ilha de Santa Catarina, possui uma grande plasticidade no uso de hábitats, além de um conjunto variado de comportamentos.
The ecology of the bottlenose dolphin (Tursiops truncatus) is scarcely documented in Brazil. The objective of this article is to present information about the distribution, group size and behavior of T. truncatus collected oportunistically around the Island of Santa Catarina. Locality, date and time, group size and behavior were registered after each opportunistic sighting. Seventy-one groups were observed between 1989 and 2005, in all months of the year. The species was sighted along all the coast of the island, using a great variety of habitats including protected bays and exposed beaches. Group size varied from 1 to 200 individuals, with a mean group size of approximately 8 individuals (mode = 2). Interactions with three species of sea birds were also documented. Data presented here suggest that the species is common around the Island of Santa Catarina, has a great plasticity in habitat use, and a varied behavior repertoire.