Passive acoustic monitoring of river dolphin (Inia geoffrensis and Sotalia fluviatilis) presence:

Charles A Muirhead

doi:10.5597/lajam00265

Abstract

All river dolphin species are in decline as a direct result of intensified anthropogenic activity along river systems. In South America, the size and geographical complexity of their range pose a challenge to status assessment. Passive acoustic monitoring offers a cost-effective, scalable, and readily standardized method for determining species distribution and can augment the spatiotemporal coverage of visual survey efforts currently underway. A passive acoustic survey of dolphin presence was conducted in two areas of the Amazon River subject to different degrees of human use; the inland port city Iquitos and the Pacaya-Samiria National Reserve, in Peru. Surveys were based on acoustic detection of biosonar activity. Recorders were distributed at 17 sites along 61 linear km of river habitat for durations of 46 to 148 h. Dolphin presence was 45% lower near the city than in the reserve. This study demonstrates the efficacy of acoustic monitoring as a method for testing dolphin redistribution and/or decline hypotheses in the context of anthropogenic development. The methods are applicable to continuous future monitoring and status assessment of river dolphins in South America as well as in Asia.

Highlights

Water development projects, land use change, contamination, and intensified fishing practices are known factors contributing to the probable extinction of the Yangtze river dolphin (Lipotes vexillifer) and declining populations of the South Asian river dolphin (Platanista spp.), Irrawady dolphin (Orcaella brevirostris), and finless porpoise (Neophocaena a. asiaeorientalis)
Study Areas A passive acoustic survey of dolphin presence was conducted in two areas of the Amazon watershed of northern Peru: Iquitos and the Pacaya-Samiria National Reserve (PSNR) (Fig. 1)
In both the Iquitos and PSNR study areas the confluences with main channels (Amazon and Marañon, respectively) were most heavily occupied by dolphins, while in all four rivers studied (Nanay, Itaya, Yanayacu, and Pucate), presence was lower at upstream recording sites than at their downstream outlets

Summary

Introduction

Land use change, contamination, and intensified fishing practices are known factors contributing to the probable extinction of the Yangtze river dolphin (Lipotes vexillifer) and declining populations of the South Asian river dolphin (Platanista spp.), Irrawady dolphin (Orcaella brevirostris), and finless porpoise (Neophocaena a. asiaeorientalis). Not yet as extensive, river system development in South America is following a similar path as that of Asia, with analogous impacts on dolphin species likely to follow. Both the Amazon river dolphin or boto (Inia geoffrensis) and the the tucuxi dolphin (Sotalia fluviatilis) were categorized as endangered (da Silva et al, 2018b; 2020). Indicate that declines and redistributions of populations related to anthropogenic activity are occurring in specific locations of the Amazon and Orinoco river systems (Gómez-Salazar et al, 2012a; Pavanato et al 2012a; Araújo and Wang, 2015; da Silva et al, 2018a). These studies cover only a small fraction of the species’ ranges, it is likely that they are representative of population trends occurring throughout the Amazon and Orinoco river systems (da Silva et al, 2018a, b)

Methods

Results

Conclusion