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

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 Cananéia Estuary (CE) (25° 01' S and 47° 55' W) from July 2004 to March 2008, as well as in the Paranaguá Estuarine Complex (PEC) (25° 24' S and 48° 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 (χ² = 22.84; d.f. = 3, p < 0.05), while in the PEC no differences were reported when comparing seabird species (χ² = 5.78; d.f.=3, p = 0.1223). In the CE, feeding associations were significantly more frequent in inner waters (subset A0; χ² = 9.52; d.f. = 2, p < 0.05), and in winter (χ² = 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 (χ² = 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 (χ² = 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.Keywords: Cetacea, feeding associations, Sotalia guianensis, seabirds, multi-species interactions. Associações de alimentação entre o boto-cinza (Sotalia guianensis) (Van Bénèden, 1864) e aves marinhas no estuário do Lagamar, BrasilResumo O objetivo principal do presente estudo foi de descrever as características a respeito das associações de alimentação entre o boto-cinza, Sotalia guianensis, e aves marinhas em duas áreas distintas do estuário do Lagamar, Brasil. Investigações efetuadas a partir de embarcação e direcionadas a estudos de foto-identificação de S. guianensis foram conduzidas (χ² = 5,78; g.l. = 3, p = 0,1223). No EC, associações de alimentação foram significativamente mais freqüentes em águas internas (χ² = 9,52; g.l. = 2, p < 0,05) e no inverno Santos, MCO. et al.

Habitat overlap between bottlenose dolphins and seabirds: a pilot study to identify high-presence coastal areas in the Tyrrhenian Sea

“…Dolphin and seabird foraging were most frequent at the mouths of the two most important river basins in the area, the Fiora and Mignone. This is in agreement with previous studies that documented high numbers of bottlenose dolphins at the mouths of rivers, such as the Magra river (Ligurian Sea) (Alessi & Fiori, 2014), the Shannon estuary (Ireland's west coast) (Ingram & Rogan, 2002) and the Lagamar Delta (Brazil) (Santos et al ., 2010). Rivers play an important role, at a small scale, in affecting water temperature and salinity values and in defining sediment distribution.…”

“…However, although these associations have been documented locally, e.g. in the Ebro delta (Witt et al ., 1982) and the Lagamar estuary (Santos et al , 2010), their relevance at the ecosystem level remains unknown, mainly because they constitute relatively rare events or are difficult to detect (Thiebot & Weimerskirch, 2013). At large spatial scales, seabird prey items are not always accessible near the sea surface, and it has been well-documented that most seabirds seem to search actively for physical features, such as upwellings or oceanic frontal zones and shallow areas (Schneider, 1991; Hunt et al ., 1999; Bost et al , 2009) that increase the accessibility of the target species near the surface.…”

Interactions between Manta birostris and Sotalia guianensis in a World Heritage listed Brazilian estuary

“…The context of both behavioural interactions and the known learning capacity and recognition skill of cetaceans, including S. guianensis , support earlier studies on avian–delphinid interactions (Santos et al ., ). According to Würsig & Würsig (), in some associations delphinids probably recognize avian foraging strategies before moving to the area and initiating their own foraging behaviour.…”

“…1), the environmental conditions in the PEC promote gradients of diverse microhabitats and large spatio-temporal variations in resident and transient ichthyofauna, several of which are targeted by artisanal fisheries (Possatto et al, 2016). The PEC also supports >80 and 20 species of elasmobranchs and marine mammals, respectively (many of which are classified as vulnerable to critically endangered; MMA, 2014), including M. birostris and S. guianensis (Bornatowski et al, 2009;Santos et al, 2010).…”

“…Like other delphinids, S. guianensis exploits opportunities in its immediate environment to facilitate predation, including utilizing boats, pier foundations, beach topography or even fishing gear to herd and disorientate ichthyofauna (Monteiro‐Filho, ). Their opportunistic behaviour also frequently encompasses foraging interactions with birds (Santos et al ., ), but few (if any) such associations with elasmobranchs have been described in the literature.…”