Tara and Scott SCUBA along the Wall at Runway Ten, 15 m deep, San Salvador, Bahamas.
The Neotropical otter is a unique component of the Neotropical ecosystem. Although the Giant otter is prevalent in the southern part of the Neotropics, especially in the Amazon basin, the Neotropical otter is the only species of otter found in Costa Rica. Primarily as a result of poaching, water pollution, and habitat loss, the Neotropical otter has been put on the list of endangered species (although it is currently listed as Ňdata deficientÓ for reasons that will be addressed later). In any case, advances in wildlife conservation have attempted to make the future of this species more promising.
Sometimes billed explicitly as the Neotropical river otter, this species is indeed found exclusively in freshwater riverine habitats. It has been suggested that the Neotropical otter prefers quick moving rivers and is less likely to be found in still-water environments (Otternet 1998). Their geographic range is the greatest of the three freshwater species in the Lontra genus, ranging from Mexico to as far south as northern Argentina (Beletsky 1998). Physically, the Neotropical otter is distinguishable by its relatively small size, differentiating it from the appreciably larger and aptly named Giant otter in places where those species cohabitate. Typically weighing less than 12 kilograms, its total body length ranges from approximately 900 to 1360 millimeters with the tail accounting for up to one-third of the total body length (Otternet 1998). The tail is wide and becomes very thick at the base. Males are generally significantly larger than females, weighing on average 20-25% more. Additionally, the males are observed to have broader heads than the females and they swim with their tails skimming the surface of the water (Kruuk 1995). In color, they are varying shades of brown with gray underfur and there is notable variation in appearance of individuals within a population. Their feet have powerful claws and are webbed, an adaptation for efficient swimming as it spends most of the day in the water (Chanin 1985). It should be noted at this point that there is limited data on this particular species and accordingly, much of the behaviors and other characteristic that will be discussed in the following are not necessarily specific to only the Neotropical otter, but rather, generalizations that can be drawn for all species of river otters.
Neotropical otters, like most river otters, are piscivores, subsisting almost exclusively on the fish and crustaceans that abound in the Neotropical rivers and streams. Nevertheless, they are classified as opportunistic carnivores and would not reject an available meal of insects or small reptiles and mammals (Chanin 1985). Daily, they consume about 15-20% of their body weight. Sea otters tend to feed along the coast and for that reason it is possible to empirically determine their feeding habits, however, this is not the case for river otters. Most of the data collected about the diets and feeding behavior of river otters is from scat samples (or more specifically, spraint, a term coined by British hunters to denote otter droppings) and otters in captivity. Fish scales and bones are easily identifiable in a scat sample. In the case of the otters in captivity, it can only be inferred that they will exhibit equivalent behaviors in their natural habitats (and of course, great measures are taken to replicate their natural habitat in captivity).
River otters catch fish by actively pursuing them until they can overtake the fish or the fish is exhausted. A fish can swim at speeds up to ten body lengths per second (for very short time intervals) and thus large fish swim faster than smaller fish. An otter thus has the option of expending less energy to catch a small fish or expending more energy to catch a large fish but get a greater yield of energy from the more plentiful food source. To date, there is not sufficient data to determine conclusively which of these options river otters prefer in various circumstances. It is worth noting, however, that otters in captivity have been observed to be more apt to pursue slower moving ill or injured fish. Otters sense fish usually by sight alone, however, in murkier water they are able to rely on their facial whiskers which are sensitive to vibrations caused by moving organisms in the water. An otter will dive down to pursue fish swimming below the surface, but rarely more than two to three meters although they have reported to dive as deep as eighteen meters in extreme cases. Successful dives that result in a catch are usually shorter in duration than unsuccessful dives. Otters generally swim below the targeted fish in an effort to be minimally conspicuous. When chasing a fish, the otter can continue to follow it if the otterŐs following distance does not exceed two to three meters, and less in murkier water. Should the otter lag this critical distance, it will concede to that fish and search for another. Otters need to come up for air every 20 to 30 seconds and they are coordinated enough that this does not necessarily disrupt their rhythm as they are pursuing a quickly swimming fish. A certain myth has been perpetuated that otters will only eat part of an organism and leave the rest behind, however, this has only been observed in isolated cases (for example, eating only the liver of a fish), and it is rare for an otter to even leave behind the bones. They devour all parts of the animal and what cannot be digested remains intact in the droppings which thus provide a fairly reliable record as to what the otter has consumed. Otters are solitary creatures and accordingly hunt alone. The only exception is a mother with cubs. When the cubs are old enough to hunt actively but perhaps not quite ŇpolishedÓ hunters yet, mothers have been observed to hunt cooperatively with them (Chanin 1985).
Otters are noted for their high basal metabolic rate which is necessary for them to survive their characteristic lifestyle. Swimming and diving require large energy expenditures and it is consequently a necessity that they metabolize their food quickly and efficiently to restock their energy reserves. Otters in cold water environments expend even more energy to maintain a steady body temperature without possessing a thick layer of blubber like some marine mammals. The Neotropical otter, however, does not have this problem since it has the good fortune of living in a warm water habitat. Still, when the water temperature cools (at night, for example), the Neotropical otter does indeed expend more energy while swimming. Night activity is relatively uncommon amongst otters, perhaps related in part to this reason (Kruuk 1995).
Neotropical otters can produce offspring year round but it is most common for this species to do so in the spring. A typical gestation period is fifty-six days, after which the young are born blind but with a full coat of fur. Litters can contains anywhere from one to five cubs but the average is between two and three. The males spend no time with the young and do not provide any care as otters are very much solitary animals. After about forty-four days, the cubs can open their eyes and are able to venture outside the nest shortly after. It is not until they are about seventy-four days old that they will enter the water with their mother (Berry 2000). The development of river otters is rather slow despite the nutrient-rich milk from the mother. At the age that the river otter is just entering the water, the genetically similar mink of the same age can already swim independently (Chanin 1985). River otters are even more solitary than sea otters, so it is a challenge for the males to locate a suitable female. For this reason it is advantageous that there is a specific mating season since all individuals know internally when to seek out a mate. Incidentally, the mating season for the more communal sea otter is less clearly defined (Chanin 1985). The Neotropical otter, and most species of otter, have been observed to exhibit the behavior of scent marking which is likely used at least in part to attract a mate (Berry 2000).
Neotropical otters have several natural predators to contend with. Most noteworthy are the jaguar, anaconda, caiman, birds of prey, and domestic dogs (Berry 2000). The dangerous species to otters, however, are undoubtedly humans. There are records of humans hunting otters as early as one thousand years ago, but until about two hundred years ago, otters were able to resist significant population declines a result of humans. They have been frequently dismissed as a pest which has resulted in widespread hunting. Hunters have also taken to killing otters for sport often with the aid of ŇOtterhoundsÓ, dogs with an apparent gift for sniffing out otters (Chanin 1985). Otter fur has long been sought after and this lucrative business is the principal reason for the otterŐs decline in population. By the 1970s, as many as 30,000 river otters were killed each year in Colombia and Peru alone for their fur. The Neotropical otter in particular shows relatively little fear of humans, an unfortunate characteristic as it makes this species particularly vulnerable to poachers (Berry 2000).
Destruction of its natural habitat has also contributed to the Neotropical otterŐs decline. As the Neotropical rainforests are torn down, the otterŐs safe haven burrow along the riverŐs edge is destroyed. Because otters are primarily aquatic creatures, they are affected profoundly by water pollution. Water pollution has certainly killed much of the fish that abounds in the rivers and streams thereby diminishing the otterŐs food supply. In addition, otters that eat contaminated fish end up with the toxins in their own body (Chanin 1985).
The Neotropical otter is on the endangered species list and has been for some time. The IUCN has had it listed as Ňdata deficientÓ since 1999 because of the limited amount of information about this species throughout its wide geographic range (Waldemarin 2004). It can be presumed that this data deficiency results in part from the speciesŐ low population. In the 1970s, when populations reached an all time low, a healthy number of laws were passed protecting this species and its habitat. Essentially all countries it lives in have some type of law protecting it, enforced to varying degrees. Although still on the endangered species list, these conservation movements have effected substantial progress in rebuilding otter populations (Berry 2000). In some cases, it only took a few years for populations to grow at remarkable rates. It can only be hoped that there will continue to be even more cause for optimism about the future of this unique and vital species.
Beletsky, L. 1998. Costa Rica. New York: Academic Press.
Berry, K. 2000. "Lontra longicaudis" (On-line), Animal Diversity Web. Accessed May 17, 2007 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Lontra_longicaudis.html.
Chanin, P. 1985. The Natural History of Otters. New York: Facts on File.
Kruuk, H. 1995. Wild Otters: Predation and Population. New York: Oxford University Press.
Otternet, 1998. "Species Profile: Neotropical Otter" (On-line). Accessed 17 May 2007 at http://www.otternet.com/species/neootter.htm.
Waldemarin, H.F. 2004. Lontra longicaudis. In: IUCN 2006. 2006 IUCN Red List of Threatened Species.
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