Abstract
ABSTRACT The Neotropical otter, Lontra longicaudis (Mustelidae) is a semi-aquatic mustelid that exploits a variety of freshwater habitats. To understand the relative influence of human activities and environmental factors affecting its distribution and habitat use, we conducted systematic, seasonal surveys of otter signs along the middle Guamá River, in Pará state in the eastern Brazilian Amazon. We applied generalized additive models to compare distribution of otters along the river with data collected on environmental factors (landcover type derived from satellite imagery, and in situ measurements of physicochemical water characteristics) and anthropogenic factors (fishing gear in the river and human habitation along the river). Most otter signs (indicators of otter habitat use) occurred along the shoreline of the main river channel during the dry season; we observed fewer signs during peak flow, probably because the shoreline and floodplain are flooded, which hid signs and made access to the floodplain difficult. The best-fit model included variables for proportion of forest, presence of fishing gear and boats, bank steepness, and presence of rock formations and sand banks. Otter occurrence was negatively related to forested area and positively related to the presence of fishing gear and boats. Otters are likely attracted to fish trapped in fishing gear because they can easily predate on the trapped fish.
Highlights
River otters are semi-aquatic, territorial predators that exploit a variety of riparian habitats
We found no relationship between otter signs and amount of rainfall during the month of survey
Otter signs mainly occurred on the riverbanks (62%) and on downed tree trunks (30%), whereas sightings were mostly of otters swimming in the main channel of the river (8% of all records)
Summary
River otters are semi-aquatic, territorial predators that exploit a variety of riparian habitats. Signs (indicators of habitat use), such as feces and footprints of Eurasian otters (Lutra lutra) primarily occur along river margins of mostly intact riparian forests, which may be due to the fact that otter signs are better preserved in intact environments than in altered habitats (Jenkins and Burrows 1980). In altered environments, where riverbanks are more exposed (cleared of native vegetation), Eurasian otters tend to mark their territories more frequently with feces (Kruuk and Hewson 1978). Two key factors influencing how otters use their habitat are availability of resources and the degree to which riparian habitats have been altered by humans (Arellano Nicolás et al 2012)
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