Seasonal movements of river dolphins (Inia geoffrensis) in a protected Amazonian floodplain

Abstract

Deliberate killing for use as bait in a regional catfish (Calophysus macropterus) fishery is the primary threat affecting the survival of the Amazon river dolphin, or boto (Inia geoffrensis). Establishing and improving freshwater protected areas has been suggested as a possible course of action to protect the species. However, the ecology of the boto is poorly understood and more information is needed on the species’ habitat use and movement patterns to ensure that spatial protection initiatives meet conservation needs. In this study, mark‐recapture/resight data collected in and near the Mamirauá Sustainable Development Reserve, a várzea in the Brazilian Amazon, was used to examine transition probabilities of botos between various habitat types. Our findings suggest that it is imperative that spatial protection initiatives focused on the boto take into account the importance of várzea habitat and bay systems for individuals in early life stages. Moreover, because botos frequently occupy the main rivers, particularly during the low water period, protecting areas of the main river waters adjacent to várzeas could aid in the protection of hunted populations.

Home range and movements of Amazon river dolphins Inia geoffrensis in the Amazon and Orinoco river basins

“…The spatial ecology of Amazon river dolphins (including estimates of home ranges, movements, and habitat use) has been assessed with a variety of methods, such as: (1) strip-width transects (McGuire & Winemiller 1998, Aliaga-Rossel 2002, Martin & da Silva 2004a, Denkinger 2010 (Martin & da Silva 2004a, Mintzer et al 2016; and (4) tagging with VHF radio transmitters (Martin & da Silva 1998, 2004b. Nevertheless, there are still several unanswered questions regarding the habitat selection of dolphins.…”

“…Considered as Endangered (da Silva et al 2018), Amazon river dolphins are among the most threatened aquatic mammals. Their populations are declining due to (1) deliberate killing and bycatch (Trujillo et al 2010, Mintzer et al 2016, da Silva et al 2018; (2) habitat degradation through timber exploitation, agricultural expansion, and gold mining;…”

In-stream habitat availability for river dolphins in response to flow: Use of ecological integrity to manage river flows

“…As the monsoon starts with the average 90% exceedance flow of 672 m 3 /s in June, unusable habitats in the main stream with flow >600 m 3 /s (Fig 4) trigger GRD to migrate to a tributary (Mohana River; starts from the first week of June; personal observation), which offers seasonal refuge and suggests that a seasonal high flow has a major influence on shaping the life-history patterns of river dolphins. Similar high flow-regulated seasonal migration patterns are exhibited by river dolphins in an Amazonian floodplain [47]. As the river dolphins' birthing peak is during low water season [48], such high flow with the potential of physical disturbance immediately after the birth may pose a risk of recruitment failure for young calves [49].…”

Estimating the length of dolphins using photographs where another animal of known or estimated length is in close proximity

“…It has become the main tool for recognizing marked botos (Amazon river dolphins, Inia geoffrensis ) in a population that has been studied for 25 yr in and near the Mamirauá Reserve, Amazonas State, Brazil (da Silva and Martin ; Martin and da Silva ; Mintzer et al . ). Up to the end of 2016, more than 650 animals had been uniquely marked, and daily observations typically yield photographs identifying 20–50 individuals.…”