Feeding associations between Guiana dolphins, Sotalia guianensis (Van Beneden, 1864) and seabirds in the Lagamar estuary, Brazil

Author(s)

Santos, M. C. O. ^[1] ; Oshima, J. E. F. ^[1] ; Pacifico, E. S. ^[1] ; Silva, E. ^[1]

Affiliation

^[1] Univ Estadual Paulista Julia de Mesquita Filho UN, Inst Biociencias, Dept Zool, Projeto Atlantis, Lab Biol Conservacao Cetaceos, BR-13506900 Rio Claro, SP - Brazil

• Document type: Journal article
• Source: Brazilian Journal of Biology; v. 70, n. 1, p. 9-17, FEB 2010.
• Web of Science Citations: 3

Abstract

The main objective of the present study was to describe the characteristics regarding interactions between Guiana dolphins, Sotalia guianensis and seabirds in feeding associations in two distinct areas of the Lagamar estuary, Brazil. Boat-based surveys directed towards photo-identification studies of S. guianensis were conducted in the Cananeia Estuary (CE) (25 degrees 01' S and 47 degrees 55' W) from July 2004 to March 2008, as well as in the Paranagua Estuarine Complex (PEC) (25 degrees 24' S and 48 degrees 24' W) from April 2006 to February 2008. On all occasions when seabirds were observed engaging in multi-species feeding associations with S. guianensis, data on species involved and their numbers were gathered. From 435 observed groups of S. guianensis in the CE, 38 (8.7%) involved interactions with seabirds. In the PEC, from the 286 observed groups, 32 (11.2%) involved the mentioned interactions. The following seabirds were observed in feeding associations with S. guianensis: Fregata magnificens, Sula leucogaster, Phalacrocorax brasilianus, and Sterna sp. In the CE, S. leucogaster was more commonly observed in feeding associations with Guiana dolphins (chi(2) = 22.84; d.f. = 3, p < 0.05), while in the PEC no differences were reported when comparing seabird species (chi(2) = 5.78; d.f. = 3, p = 0.1223). In the CE, feeding associations were significantly more frequent in inner waters (subset A0; chi(2) = 9.52; d.f. = 2, p < 0.05), and in winter (chi(2) = 12.46; d.f. = 1, p < 0.05). Within these events, 44.7% of the association groups were composed by more than one seabird species. Seasonality in feeding associations was also observed in the PEC (chi(2) = 4.76; d.f. = 1, p < 0.05), with same patterns observed in the CE. Interactions were more frequent in inner waters of the Laranjeiras bay, PEC (chi(2) = 11.65; d.f. = 2, p < 0.05). Within these events, 74.2% of the association groups were composed by more than one seabird species. Water transparency, prey and seabird abundance and distribution, cetacean group size, and the life cycle of prey and seabirds are listed as the main factors addressing multi-species feeding associations in the Lagamar estuary. (AU)