Critter Corner No. 10 – The River Otter

OtterBy George Sly Goose Pond FWA has gained a well-deserved reputation as a site for spotting rare birds. Now we can add a mammal to the category of rarities. On Dec. 17th, 2015, during the GPFWA Christmas Bird Count, Sandy and Jeff Belth of Bloomington spotted a river otter on the property. CBC compiler Lee Sterrenburg noted that this is not only a first for the property but is likely the first river otter record for Greene County. The IDNR’s distribution map currently shows this species as absent from the county. The river otter (Lontra canadensis) is a member of the same Family of mammals (Mustelidae) which includes the mink, long-tailed weasel, least weasel, and badger. In other words, we could think of it as a big, aquatic weasel. River otters were once abundant throughout the state of Indiana. From pioneer times, the lure of their luxurious fur attracted trappers. This combined with habitat loss and water pollution worked against the river otter and by 1942 it had been extirpated in the state. Between 1995 and 1999, 303 river otters were released in northern and southern Indiana. The first 25, brought in from Louisiana, were set free at Muscatatuck NWR. The reintroduction has been extremely successful with river otters now occurring in all but 12 counties in Indiana. The species was removed from the state endangered list in 2005. In fact, river otter populations have grown to such an extent that the Natural Resources Commission recently proposed that a limited trapping season be instituted. Fish are the primary prey of river otters and thus it is no surprise that they favor aquatic habitats such as lakes, rivers, streams, and ponds. Sleek of build, with a flattened head for lessened friction drag, otters are amazing swimmers. The feet are webbed for swimming but, when moving through the water at high speed, the whole body and tail undulate in the typical aquatic mammal pattern. In addition to fish, river otters will eat other aquatic prey such as crayfish, frogs, mussels, and insects. The reproductive behavior of river otters is interesting in that they, like many other mustelids, exhibit delayed implantation. Mating occurs most often in the spring (March-April) but the fertilized egg does not implant in the uterine wall immediately. Implantation is delayed for several months. As a result, although the actual gestation period averages about six weeks, the young are born the following spring. Average litter size is 2 to 4. Delayed implantation seems to be associated with life in temperate climates and longer life spans. However, the adaptive value of such a diapause seems to be poorly understood. ( Otters den most often along the bank of their aquatic habitat. They may use natural tunnels for their dens but have also been known to eject the original builder, a beaver or muskrat for example. Otters in general are often described as curious and playful. Personal observations have convinced me that they are. My wife and I escaped to Florida this winter and in the canal behind our house lived river otters. Occasionally they would come by our boat dock for a visit. Coming to the shore, or actually climbing up on the dock, they would linger and peer up at us as inquisitively as we watched them. We would often see them nudging a leaf or potential food item through the water with their nose. Releasing it, they would dive in their wonderfully graceful manner only to return for more play. Many years ago, we visited Peace Corps colleagues in Thailand who had two small-clawed otters living in their house. These are small, Asian relatives of our river otter. The two bundles of energy seemed to spend most of their day at play racing through the house in a game of “catch me if you can”. One of their favorite toys was a wooden box containing a ball. There was a hole in the box through which the otters could reach and thus grasp the ball. However, the hole was too small to allow them to pull the ball out with their paw wrapped around it. As we sat and chatted with our hosts, the otters would race into the living room tumbling over one another. Suddenly, as if seized by a momentary obsession, one of them would run to the box and insert a front paw. With a look of intense concentration, it would manipulate the ball for a few seconds. After what seemed to be a most pleasing bout of tactile stimulation, it would withdraw its paw and shoot off into another room with its partner in full chase. It did indeed look like loads of fun. River otters do occasionally conflict with the interests of humans. This most often occurs when otters choose a private pond or fish hatchery as their larder. With the increase in river otter numbers in the state has come a rise in the number of damage grievances filed. In 2011 the DNR received 34 such complaints. In 2012 the number rose to 69 and, in 2013, 86 complaints were noted. Fencing has been suggested as one method for preventing such depredations. It should be noted that river otters prey heavily upon slower moving, nongame fish species (Whitaker, 2010). These include suckers, chubs, dace, and darters. However, they do not eschew bluegills and other sunfish. As adults, river otters have few enemies other than humans. However, their young may be vulnerable to predators such as coyotes and bobcats. Perhaps the recent arrival of the river otter at GPFWA is a harbinger of things to come. Although some might begrudge this fish-eating species as a competitor, it does represent the return of an Indiana native. The presence of the river otter is but one more example of the oft-cited adage – “build it and they will come”. We have certainly seen this to be true in regards to the avian visitors and residents of Goose Pond. Perhaps we will now see the palette of mammalian species inhabiting the GPFWA ecosystem become more brilliant as well. Useful Resources Whitaker, Jr., John O. 2010. Mammals of Indiana. A Field Guide. Indiana University Press. Bloomington. *otter photo courtesy of Indiana Public Media