The hunt for the giant otter

They’re large and they hunt in packs, so giant otters ought to be easy to study. Sophie Stafford put her tracking skills to the test in Brazil’s Pantanal.

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Giant otter article
 
The giant otters are another matter. Despite their large size (about the same as a German shepherd dog), and their habit of travelling in groups, giants can be surprisingly hard to find. So the researchers often have to content themselves with merely spotting signs of their presence. From the boats, they scour the banks for denning sites, footprints, resting places, ‘campsites’ and spraints (scats). 
 
The giants modify areas of riverbank they use regularly by removing dry leaves and impeding the sprouting of new vegetation – tell-tale signs for keen-eyed researchers who are also on the lookout for active dens, which can be identified by fresh yellow sand cascading down the banks. 
 
Giants also like to rest up for long periods in campsites, which they clear of vegetation and mark in an unusual way – by squirting lots of watery faeces all over the area and then using their forepaws in a strange, circular, waddling motion to mix them in with the soil and sand.
 
No one is entirely sure why they do this, but it is thought that it serves to fix their smell in the soil as a territorial marker.
 
So dedicated are the Earthwatch scientists that spotting one of these giant spraints is a source of great delight. With a nimbleness born of months in a canoe, Miguel leaps from the vessel onto the bank and, armed only with a plastic bag and a pen, goes in to collect the smelly mess.
 
Every spraint, whether it is on land or tree, fresh and fragrant or old and dry, receives the same treatment, and is lovingly recorded and scraped into a polythene bag to be taken back to the research station for analysis.
 
Someone’s got to do it
 
So why the faecal fanaticism? The researchers are trying to determine whether neotropical otters compete with the giants for food. So far, their research suggests that, though both species are primarily piscivorous, giant otters feed on bigger fish than neotropicals. While the giants favour large catfish and perch, the neotropicals feed mainly on small fish.
 
This difference in diet may also explain why the two otter species are rarely found in the same part of the river. The scientists believe that the ever-elusive giants hide out in the Rio Negro’s many landlocked oxbow lakes and creeks, where their large fish prey is easier to catch, due to the shallow water and closed environment. The neotropicals, by contrast, are more likely to be found hunting in the deeper margins of the main river.
 
Exploring the oxbows is challenging – not only do the canoes have to be carried for short distances, but sometimes you have no choice but to get out and walk. After Ellen Wang’s words of caution, I was surprised (to say the least) to find myself wading knee-deep in the Rio Negro’s caiman- and piranha-infested waters, with mud and who-knows-what-else squelching between my toes.
 
Miguel did offer to carry me, but then I would have been deprived of the experience of having my feet nibbled by small fish. As I watched bemused, a brigade of misguided cleaner fish (lambari) sucked enthusiastically at my toes. “They usually clean the ticks off the capybaras’ legs,” explained Miguel, hiding a smile. “So perhaps they mistake the moles on your feet for ticks.”
 
Over the next two weeks, signs of the giants’ presence were abundant (and other people saw them), but to me the animals themselves remained elusive. As we sat patiently watching an empty river for several hours, it struck me that to be an otter researcher you need special skills. You must be able to distinguish at a glance between a swimming otter and an emergent branch, caiman snout or leaping fish – not as easy as it sounds.
 
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