Abstract
A long-term study of a common bottlenose dolphin (Tursiops truncatus) population inhabiting the Gulf of Guayaquil, Ecuador (2o33' S, 79o20'W), has been carried out for almost 30 years. Similarly, as in other parts of the world, this population is structured socially and spatially in well-defined subunits or communities. Two of these communities, referred to as Posorja and El Morro, have been studied with major intensity in the last 10 years in the western inner estuary, among others to calculate population parameters that allow assessing their viability in time. Calculated parameters include annual abundance, age and sex composition, annual crude birth rate, calf survival, calf production interval, and average annual mortality/emigration. With these parameters and others derived from other better-studied populations, the trend of both subunits was modeled using the software Vortex. Results show that even under an optimistic scenery both communities will be extinct in the short (Posorja) and mid-term (El Morro), if current stressors continue. Most population parameters calculated in both communities show similar values as in populations elsewhere, but a very low calf survival in Posorja and high mortality/emigration ratios in adults, and probably in juveniles in both communities, contribute to revert this trend. Population deterioration seems to be the result of different human-induced threats such as fisheries, maritime traffic and others still not well assessed, as well as stochastic demographic events. We recommend taking actions in the short term to halt population decline addressing the major causes of mortality affecting these dolphin communities.
Highlights
The conservation status of several species of coastal small cetaceans is of worldwide concern because of the increasing evidence of population declines, in some cases to critical levels, those species of discrete distribution (e.g., Slooten, 2007; Huang et al, 2014; Taylor et al, 2016; Minton et al, 2017)
We evaluate population parameters of two neighboring population units of bottlenose dolphins inhabiting estuarine waters in the Gulf of Guayaquil, Ecuador, aiming at defining their viability in the short and medium-term
The two bottlenose dolphin communities assessed in this study show negative trends that may be irreversible if the causes of such condition are not addressed in the short term, especially for the Posorja community is experiencing a decreasing trend for at least 15 years (Jiménez and Alava, 2014; Félix et al, 2017)
Summary
The conservation status of several species of coastal small cetaceans is of worldwide concern because of the increasing evidence of population declines, in some cases to critical levels, those species of discrete distribution (e.g., Slooten, 2007; Huang et al, 2014; Taylor et al, 2016; Minton et al, 2017). The role of marine mammals in the ecosystem and how changes in the trophic structure could affect them is not known in depth (see Morissette et al, 2012), as changes could be exacerbated by alterations generated by both human activities and large-scale phenomena such as climate change acting synergistically (Wells, 2010; Wild et al, 2019). Addressing the conservation problem of small cetaceans is complex, and requires financial and human resources to improve our understanding of the ecosystem functioning and how wild populations respond to both natural and humaninduced pressures
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
