The Neotropical Otter (or Neotropical River Otter), Lontra longicaudis, is probably our rarest resident mammal. We might have only one or two resident adults in our Rio Zunac Reserve, and there are no recent reports from any of our other reserves. This otter is very similar to the familiar North American River Otter (Lontra canadensis). It can reach about a meter and a half in length, and lives only along bodies of water. It eats mostly fish, though it sometimes catches aquatic birds and other prey. It has a thick fur coat which traps air to keep it warm in cold water. This nice warm fur led humans to trap it and export the pelts (just like they did to the Sea Otter and other otters throughout the world). This caused local extinctions, but a couple of decades ago the Convention on International Trade in Endangered Species (CITES) was passed, prohibiting international trade in products derived from vulnerable species. Our Neotropical Otter was listed as a CITES Appendix 1 species, giving it the highest level of protection, so it is no longer hunted for its fur.
People still Neotropical Otters for fun, or because otters eat fish that humans want. I once came across some hunters in the nearby Rio Topo, intently aiming their rifles at a spot in the water in front of an enormous (10m long) rock. They were on the opposite side of the river from me. I watched the otter they were hunting slip around the backside of this big rock. It sneaked around the rock and into the water downstream, while the hunters kept staring intently at the upstream side of the rock, waiting for the otter…
Our Rio Zunac otters surely follow the river down to its confluence with the much larger Rio Pastaza, a major tributary of the Amazon, about 5 km from our reserve. The mouth of the Rio Topo, where I watched the otter outsmart those hunters, is just a few tens of meters away from the mouth of the Rio Zunac. The Rio Topo is considerably longer and wider than the Rio Zunac, and has its headwaters in the vast chain of lakes and marshes in the alpine grasslands of the Llanganates National Park, so I suspect the Rio Topo is probably the center of the local otter population. Unfortunately the lower Rio Topo is the site of a hydroelectric project under construction, along with several more in the planning stages, so it is likely that this population will be cut off from the Rio Zunac soon. I don’t know if our animals will form a viable population if they are cut off from the Topo. Maybe the Rio Pastaza itself provides enough additional habitat to support a viable population, but our otters will soon be cut off from much of that too, after the construction of the proposed Abitagua hydroelectric dam in the Rio Pastaza just a few meters downstream from the mouth of the Rio Zunac. Other projects are proposed in the Rio Pastaza upstream from the Zunac, and there are rumors of plans for a tunnel to capture the Rio Zunac itself. I do not think our otters will be with us for long.
Evolutionary history of the Neotropical Otter
Otters apparently arose in Eurasia, and are most closely related to the mink. The ancestors of the Neotropical Otter, like those of the Spectacled Bear, originally crossed into North America via periodic land bridges across the Bering Sea. The common ancestor of the three extant South American Lontra otters (the Neotropical Otter, the Marine Otter, and the Southern River Otter) migrated into South America when the Isthmus of Panama rose up and connected those two continents about 3-5 million years ago. Recent genetic studies (Vianna et al 2010, Trinca et al 2012) show that ancestral river otters spread rapidly through South America. The Central and South American river otters diverged from the ancestors of the North American river otter about 3 million years ago. Once they reached South America, the ones colonizing the extreme southern cone diverged from the rest about five hundred thousand years ago, to become the Southern (or Chilean) river otter, Lontra provocax. The coastal populations of Southern River Otter then began to adapt to marine conditions, diverging from L. provocax about 300000 years ago to become the Marine Otter, L. felina.
Neotropical Otters show some geographic variation in skull shape through its wide range (currently Mexico to the subtropics of South America), and some people thought the otter may actually consist of several very similar species. The publication last year of a study by Trinca et al. (2012) showed that there is indeed quite a lot of genetic divergence between otters from different regions of South America. The most distinctive population is the Colombian one from the Rio Magdalena, which flows into the Caribbean Sea and is isolated from the Orinoco and Amazon drainages. There is also a genetically distinct population in Bolivia. The rest of the South American population is divided into two units, a Guianan/ Venezualan/ Peruvian/ Ecuadorian?/ Northern Brazilian population, and a southeastern South American population. (No samples were taken from Ecuador so I am only guessing about where the eastern Ecuadorian otters belong). For those of you who know genetics, the value of the genetic “differentiation” measure Fst between mitochondrial alleles of these two populations was high, 0.6 to 0.7. One of these days I’ll write about why Fst is not really a valid measure of genetic differentiation, but in this case it is probably not misleading. It is interesting to see that in the phylogenetic tree of the Lontra otters (Trinca et al 2012), the divergence between the two major subgroups of the Neotropical Otter is older than the divergence between the Marine Otter and the Southern River Otter. This means there is a lot of regional diversity in the Neotropical Otter. I hope some day our Ecuadorian population can be analyzed so we can see how it fits into the larger picture.
There is one other species of otter in Ecuador, the Giant Otter, Pteronura brasiliensis, which lives in lowland rivers and lakes. They are very special otters, the last survivors of an ancient lineage that branched off from the rest of the world’s otters very long ago, presumably in Eurasia. Fossils of a presumed member of this lineage, Satherium, have been found in North America. The Giant Otter is endangered throughout its range but especially so in Ecuador, thanks to new roads, colonization, oil exploration and extraction, and resultant oil spills in its lowland range. This otter has been reported from the upper Rio Pastaza, and my local friends claim that it occasionally reached the mouth of the Rio Zunac and Topo. One man described to me how he shot one on the upper Rio Pastaza when he saw its head coming out of the water and thought it was a giant snake…he accurately described its distinctive pale throat and belly patch, which separates it from the Neotropical Otter. I would be amazed if any Giant Otters still survive around here. It would be nice to think they might some day return, but the future Abitagua dam will kill that hope. Forces beyond our control will determine the fate of our Neotropical Otters as well, but we will enjoy their playful presence while they are still here, and we will do what we can to protect the ones that stay in our reserve.
Trinca C et al. 2012. Phylogeography and demographic history of the Neotropical Otter (Lontra longicaudis). Journal of Heredity 103(4):479–492
Vianna JA, Ayerdi P, Medina-Vogel G, Mangel JC, Zeballos H, Apaza M, Faugeron S. 2010. Phylogeography of the marine otter (Lontra felina): historical and contemporary factors determining its distribution. J Hered. 101:676–689