Spatial Ecology Applied to Identify Differential Uses of Habitat Types and Hotspots of Amazon River Dolphin Activity

Context: Identifying the heterogeneity in the habitat use and hotspots of Amazon River dolphin activity is essential to design effective strategies for the management and conservation of these cetaceans and their habitats in the Colombian Amazonas River and Orinoco basin.Objectives: Quantify the differential use of habitat that Amazon River dolphins exhibit and to identify hotspot activity during seasons of rising waters in the Colombian Amazonas River and other major rivers in the Orinoco basin.Methods: Based on processed satellite images Landsat 8 (2018-2022), we classified habitat types used by I. geoffrensis and reported in the literature: (1) main river, (2) confluences, (3) tributaries, (4) channels, (5) islands, (6) bays, and (7) lagoons. We combined this dataset with GPS location data obtained from 17 tagged Amazon River dolphins to quantify the proportion of habitat types used, and we used GAMLSS to explore the relationship between the number of locations per habitat as the predictor variable and nine response variables. Kernel density estimate (KDE) analysis was used to identify both areas used (K95) and hotspot activity associated with core areas (K50) in the habitat types for the individuals monitored in the Amazonas River and Orinoco basin. Results: Satellite tracking of I. geoffrensis individuals reported 16.098 locations (Amazonas River, n = 2.934 locations and Orinoco basin, n = 13.164 locations) classified into seven habitat types. For the analyzed period (rising waters) main habitat types used were as follow: in the Amazonas River (1) main river (n = 1.346, 46%), and (2) lagoons (n = 1.158, 39%); and in the Orinoco basin (1) main river (n = 7.798, 59.2%), and (2) channels (n = 1.535, 11.7%). The best fitting GAMLSS for the I. geoffrensis monitored individuals in the Amazonas River showed that body length, sex, and habitat types (lagoons and main river) were significant predictors of Amazon River dolphins; and in the Orinoco basin they showed that body length, longest distance, K50, and habitat types (confluences, lagoons, main river, and tributaries) were significant. Individuals monitored in the areas evaluated in the Amazonas River reported K95 ranged: 30.7–105.5 km2 (mean = 62 ± 32), and the K50 or hotspots of activity were recorded in the main river, confluences, lagoons, and tributaries. In the five rivers of the Orinoco basin, monitored individuals registered K95 ranged: 6–116 km2 (mean = 32.8 ± 31.53), and hotspots of activity were recorded in the main river, islands, channels, confluences, bays, tributaries, and lagoons.Conclusions: Evaluation of differences in habitat type use and identification of hotspot activity will contribute to improving management and conservation efforts for the populations of these cetaceans in the Colombian Amazonas and Orinoco basins.

Current Status of the Endangered Ganges River Dolphin (Platanista Gangetica), the Aquatic Megafauna in the Brahmaputra River System

The Ganges River Dolphin (Platanista gangetica) is the most charismatic aquatic species inhabiting rivers of India, Bangladesh, and Nepal. It is an endangered species that occurs both in the Brahmaputra and Barak river systems in Assam (India). In the Brahmaputra river system, the occurence of ‘hihu’ is primarily confirmed in the mainstream Brahmaputra, the Kulsi river of Kamrup district, and the Subansiri river of Lakhimpur district. The dolphins inhabit river confluences or tributary junctions followed by river meanderings with the prevalence of eddy counter-currents and prey-fish abundance. Of late, it has been observed that river dolphin population has declined at an alarming rate due to the potential threats including poaching for dolphin oil, by-catch, overfishing, net entanglements, sand mining, habitat destruction through aquatic pollution, construction of dams, and lack of awareness. The species is left only in certain pockets of the Brahmaputra River. Thus, there is an urgent need for the conservation of this endangered species in its natural habitats. Effective protection of this endangered aquatic megafauna requires elimination and management of the potential threats. This review provides an overview of the distribution and population status, ecology, and management strategies and recommendation to increase awareness for its long-term conservation.

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

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.

Aggression towards neonates and possible infanticide in the boto, or Amazon river dolphin (Inia geoffrensis)

Recent observed attacks by male Amazon river dolphins on conspecific calves, together with post-mortem examinations, indicate that infanticide occurs in this species but that not all attacked calves are killed. If mortality occurs, it might therefore be an inadvertent consequence of the behaviour rather than the motive for it. Our observations suggest that males who commit infanticide are unlikely to gain direct fitness benefits. Evidence does not fit the sexual selection hypothesis. Aggression towards calves usually ‘drew a crowd’ and may represent socio-sexual display or simply be a form of social pathology, as found in other infanticidal mammals.

Deteriorating Habitats and Conservation Strategies to Repopulate the Endangered Indus River Dolphin (Platanista gangetica minor); a Lesson Learned From the Conservation Practices of the Yangtze Finless Porpoise (Neophocaena asiaeorientalis)

The Indus River dolphin (IRD; Platanista gangetica minor) is an endangered and blind freshwater cetacean, endemic to the Indus River system of Pakistan and India. This review article provides detailed information about the major challenges IRDs are facing, and their possible consequences on the population dynamics of the IRD. Furthermore, we have suggested future conservation strategies for the IRD based on the lesson learned from the conservation of the Yangtze finless porpoise (YFP; Neophocaena asiaeorientalis), a Critically Endangered freshwater cetacean. The major challenges for IRDs are habitat degradation, habitat fragmentation, and several types of industrial and agricultural pollutants. Worsening climatic changes, illegal fishing, and overfishing are additional threats. The construction of several barrages has fragmented the population into several short segments, some of which are too small for the IRDs to survive. In some segments, the population status of the IRD is unknown. In the remaining populations, genetic inbreeding, water shortage, canal entrapment, and altered ecological environment are potent negative factors for the survival of the IRD. Conservation strategies including fishing bans, translocation, and future research (tagging, periodic health assessments, necropsy and virtopsy, understanding the reproductive biology, and genomics) are possible recommendations. Very serious conservation efforts are needed to save the IRD from decline keeping in view the water shortage, pollution, lack of health assessment studies, and habitat degradation and fragmentation.