Challenges and priorities for river cetacean conservation

Abstract

River cetaceans are particularly vulnerable to anthropogenic impacts due to their constrained ranges in freshwater systems of China, South Asia, and South America. We undertook an exhaustive review of 280 peer-reviewed papers and grey literature reports (1998-2020) to examine the current status of knowledge regarding these cetaceans and their conservation. We aimed to better understand the scale of threats they face, and to identify and propose priority future efforts to better conserve these species. We found that the species have been studied with varying frequency and that most of the research on threats has focused on habitat degradation and fragmentation (43%, mainly driven by dams and extractive activities such as sand mining and deforestation), and fishery interactions (39%, in the form of bycatch and direct take). These threats occur across all species, but more information is needed, primarily on quantifying the population impacts as a basis for designing mitigation measures. Other threats identified include pollution, vessel collisions, traditional use, and poorly managed tourism. Emerging methods such as environmental DNA and unmanned aerial vehicles are described for studying these species. Promising conservation interventions include cetacean-specific protected areas, natural ex situ protection, community-led conservation, and education programmes. However, transnational political will is required for a step change towards broad-scale protection in freshwater environments. In addition, we propose increasing capacity building, developing management plans, working closely with fishing communities, enhancing public awareness, expanding regional collaborations, and diversifying funding.

Satellite-monitored movements of the Amazon River dolphin and considerations for their conservation

“…We therefore hypothesize that in areas with medium and high fishing catch, dolphins are more likely to be taken as bycatch. Bycatch is an understudied threat to river cetaceans because of the lack of comprehensive impact assessments and the absence of consolidated data (Raby et al, 2011; Whitty, 2016; Dewhurst-Richman et al, 2020; Campbell et al, 2022). Previous research in Peru has documented cetacean bycatch incidents in purse seine-type nets and gillnets (locally called honderas and agalleras , respectively; Campbell et al, 2020), but given the proximity of our tagged dolphins to fisheries, even in protected areas, the overlap could be higher than reported previously.…”

“…In addition, overfishing could also potentially be a threat to Amazon River dolphins (e.g. by depleting fish prey; Allan et al, 2005), although there has been only limited research on this (Campbell et al, 2022).…”

“…We gathered spatial data layers to examine the scope of three proximal anthropogenic threats that are of types considered the most significant for river cetaceans globally (Pavanato et al, 2016; Brownell et al, 2017, 2019; Campbell et al, 2022): dams, the Amazon Waterway and fisheries. The temporal span of the threat layers varies, and therefore we included layers that do not overlap completely with the tracking periods.…”

“…Data on the distribution and habitat use of aquatic mammals such as the Amazon River dolphin can be difficult to obtain, and this has been identified as a key knowledge gap for this group (Campbell et al, 2022). Many of these species are widely distributed, are highly mobile and can occur in areas that are difficult for researchers to access.…”

The Amazon River dolphin, Inia geoffrensis: What have we learned in the last two decades of research?

“…Threats to boto populations come from many sources. Herein, we highlight biological resource use (e.g., intentional hunting for bait, entanglement in fishing nets) and modification of natural systems (e.g., dam construction) as the most important threats to the species (da Silva et al, 2018c;CMP, 2020;Campbell et al, 2022).…”