Biodiversity of the Rewa Head B Zoological Society of London ...

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Method In surveying the Rewa for signs of giant otters we followed the guidelines of the IUCN/SSC Otter Specialist Group (Groenendijk et al 2005). The river was searched for sign during drifts downstream, looking out for evidence of holts, latrines or scratch walls or for the groups themselves. The position of these was recorded using GPS to delineate group territories. Group sizes were obtained by directly counting all individuals when a group was encountered in the river. We used two Canon EOS 400D cameras with 300mm and 500mm lenses to capture throat markings and a Sony Handycam mini DV. Giant otters have a unique throat pattern which can be used to identify individuals, preventing the same group being counted twice. When an active site was located, any faecal deposits evident were collected and stored in ethanol for subsequent genetic analysis. Results In the 65 miles of Rewa Head explored above Corona Falls, we found evidence of 5 groups with an estimated population size of 35 animals and collected 17 faecal samples. Due to the unseasonably heavy rains experienced it proved more difficult than anticipated to locate and observe groups. The narrow streams feeding the Rewa were full, resulting in groups spending much of their time hunting in these difficult to access creeks. We found that groups frequently had latrines at the confluence of a forest stream and the main river. Although we did not survey the Lower Rewa for giant otters, we did encounter 4 groups and collected 13 faecal samples from them. We also observed the neotropical otter (Lontra longicaudis) in the Rewa Head on four occasions and encountered two sprainting sites. While there currently appears to be no direct threat to the giant otter’s survival in the Rewa and the population appears healthy, in informal discussions with fishermen it is apparent that they view the giant otter as a competitor. Work in Bolivia, by Beccera- Cardona (2006) has shown that in rivers there, there is only a small overlap in fish species and size selection by fishermen and giant otters, however the more generalist nature of the Guyanese fishermen would inevitably lead to a degree of competition. This competition is generally tolerated, with actual killing of otters by villagers being rare. However food shortages in unproductive years might exacerbate antagonistic feeling towards giant otters leading to conflict. In the Lower Rewa evidence that the river might be mined for gold or diamonds was recorded. We found claims staked in April 2008 spread over 20 river miles. As this report was being prepared the Guyanese Government revoked all claims in the Lower Rewa and has put a moratorium on mining throughout both the Rewa Head and Lower Rewa. The giant otter is a top predator in its food chain and is thus extremely sensitive to mercury bioaccumulation. Mercury concentration has been shown to cause a range of neurological disorders, impaired reproduction and immunocompetency (Klenavic et al 2008, Fonseca et al 2005). Camera Trapping Survey In this study we used the Reconyx RC55 camera trap due to its fast ‘wake-up’ time and rate of image capture, able to record 1 frame per second. This enables a more accurate estimate to be made of animals travelling in groups. The use of digital technology proved essential in the high humidity of the forest and despite torrential rains, no camera was lost to mould. 2GB Extreme III CF cards were used and proved ample to contain all images captured. The traps were triggered by a PIR motion sensor and were mounted with an infrared LED illuminator. Camera setup was as follows. Image quality: medium; Firing delay: no delay; Firing sensitivity: extremely high. Biodiversity of the Rewa Head 13
Figure 10. Rapidity with which all 17 species of mammal recorded in the camera traps were captured. 14 Biodiversity of the Rewa Head Method Twelve Reconyx RC55 camera traps were set up along the Rewa above Corona Falls. Each trap was fixed to a tree or stake approximately 50cm above the ground. The traps were set up in pairs, with one on the river bank itself facing inland and its partner 150 metres perpendicular to the river bank facing a direction estimated to best increase the likelihood of capture. Each camera was considered a separate sampling site for determining the Relative Abundance Index (RAI). The pairs were arranged 5 miles apart and left for a maximum of 22 days before collection. While game trails were not sought for in the placement of the traps, local judgment was employed in their positioning in order to prevent focusing on dead ground. Due to the strict adherence of the 5mile/150m rule, we ensured that to some extent the placement of the traps was randomised and took in a variety of micro-habitats from dense scrubby marshland to hill tops to open riparian bush. Figure 11. Layout of the string of camera traps along the river. Results In total, 5227 camera trap hours were accumulated resulting in 214 triggering events. Of these, discounting false triggerings due to movement of leaves by wind or in cases where animals had passed too rapidly to be captured, 167 individual animals could be identified from 16 species of mammal, 5 species of bird: Black curassow (Crax alector), grey-winged trumpeter, (Psophia crepitans), grey-fronted dove, (Leptotila rufaxilla), great tinamou (Tinamus major) and cinereous tinamou (Crypturellus cinereus); and one species of reptile: the jungle runner (Ameiva ameiva). From the raw images of animals in which individual identification or sexing was impossible, we filtered the data based on the assumption that multiple firing episodes taken at the same site in the same 24 hour period constituted the same animal or group. Number of individuals was then estimated from this as 157. Number of estimated individuals for each species was then divided by this total to obtain the Relative Abundance Index (RAI).
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Page 8 and 9: Co n t e n t s Executive Summary 3
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Page 14 and 15: Unlike its larger neighbour to the
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Page 42 and 43: Groenendijk J, Hajek F, Duplaix N,
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Page 48 and 49: Scarlet Macaw Ara macao F U S Golde
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