Decreasing population trend in coastal bottlenose dolphin (Tursiops truncatus) from the Gulf of Guayaquil, Ecuador

Abstract

1. The population status of the coastal bottlenose dolphin (Tursiops truncatus) inhabiting the inner estuary of the Gulf of Guayaquil, Ecuador (3°S, 81°W) was assessed. Evaluated aspects included social organization, abundance and spatial distribution.2. Surveys focused on the western part of the estuary (Posorja and Estero Salado) but other areas in the central and eastern inner estuary were also surveyed.3. Effort included 68 trips, 5001 km of survey and 288.8 h at sea. Between 735 and 793 dolphins in 92 groups were recorded during the study. 4. Dolphins are not evenly distributed but concentrated their activities in the mouths of large channels. 5.A cluster analyses indicated that dolphins organize in partially discrete subunits referred to as communities.6. Abundance estimations were obtained using mark-recapture modelling for two communities:Posorja and Estero Salado (43 dolphins, 95% CI 37-49 and 65 dolphins, 95% CI 52-82 respectively). 7. Four demographic parameters: average size of communities, average group size, average encounter rate and average density were compared with information obtained during the 1990s. In all cases the current values were between 39 and 54% lower; in the last three cases the difference was statistically significant.8. Possible causes of this apparent decline include bycatch, ship strikes, pollution and habitat degradation; however, none of these have been assessed in depth. Most probably, different stressors are affecting dolphin communities to different extents. 9. A comprehensive assessment of the whole population inside the gulf is needed. Identifying major threats is a priority to define concrete actions to prevent further population decline.

Strand-feeding by coastal bottlenose dolphins (Tursiops truncatus) in the Gulf of Guayaquil, Ecuador

“…and catfish (Arius sp.) (Félix, 1994). Based on our data and field observations elsewhere (Hoese, 1971;Rigley et al, 1981;Dos Santos and Lacerda, 1987;Silber and Fertl, 1995;Torres and Read, 2009), we suggest that strand-feeding is an occasional foraging strategy of coastal bottlenose dolphins inhabiting estuarine waters in mangrove habitats of the Gulf of Guayaquil, and a preferred feeding activity exhibited during certain times of the month, which occurs at low tides during the full moon cycle.…”

“…To the best of our knowledge, behaviors resembling strand-feeding by bottlenose dolphins have been described very briefly without supporting photos in the inner estuary of the Gulf of Guayaquil (Félix, 1994). As a part of a long-term field study (2001-2011) on photo-identification, population ecology and monitoring of the bottlenose dolphin in the El Morro Mangrove and Wildlife Refuge, we provide some insights on its conservation, and photo-documented the occurrence of strand-feeding as a recurrent behavioral foraging tactic in this region of South America.…”

“…This small cetacean has been categorized as a vulnerable (VU) species in Ecuador due to several conservation threats according to the last update of the Ecuador's Mammals Red Data Book (Jiménez et al, 2011). The bottlenose dolphin population of the Gulf of Guayaquil has preliminarily been estimated at close to 640 individuals (Félix, 1994). This population represents a proportion of the coastal and resident animals of the inner estuary, distributed mainly along the Jambelí Channel at the east border of Puna Island (Figure 1), including the surrounding waters and northward; however, it does not represent other populations existing in adjacent areas in the Gulf (i.e.…”

“…The coastal ecotype of the bottlenose dolphin is commonly found to inhabit the Guayaquil Gulf Estuary; however, its behavioral and feeding ecology have been scarcely studied (Félix, 1994). To the best of our knowledge, behaviors resembling strand-feeding by bottlenose dolphins have been described very briefly without supporting photos in the inner estuary of the Gulf of Guayaquil (Félix, 1994).…”

“…Confirmation on fish taxonomy was accomplished through direct comparisons with the landings from artisanal fishermen at Puerto El Morro and surrounding areas, using a field guide for marine fish of Ecuador (Jiménez and Béarez, 2004), as well as earlier data by Félix (1994). The main prey was the mullet (Mugil spp.…”