OTTER, RIVER

Under Construction May 2011

RIVER OTTER

Lutra Canadensis

GUARD HAIR

Length: 25-30mm (Adorjan and Kolenosky 1969), 25 mm max (Moore et al 1974), 30mm max (Tumlison 1983), 20-25mm (ASM #1 back), 7-13mm (ASM #1 tail)

Diameter Range: 185 microns max (Moore et al 1974), 180 microns max 129 microns ave (Tumlison 1983), 155microns (ASM #1)

Medullary Index: 0.48 (ASM #1)

Medulla: Cells in the medulla not separated by pigment masses, like we see in canids. Medulla at the shield (where it is widest) was measured at 75 microns. The medulla is fragmentary at the root becoming continuous up until the tip. The medulla has cells that span the width of the medulla with shapes of bubble-like letters that are translucent. In between these cells are many very small oval cells with dark outlines that cluster together giving the medulla the appearance of having many black squiggly lines throughout. 

Color: Red-brown throughout the cortex, absent in the medulla.  Moore et al (1974) says the base should be brownish gray, with a dark brown upper shaft and a light brown tip (Moore et al 1974)

Scales: Petal-like with a tine shape particularly visible by the root leading up to the shield ( its difficult to see the scales.  At proximal end the scales are flower petal shaped where each individual scale has a single point. On one example, the flower petal-like scales extend at least half the length of the hair fiber and there are about 5-6 petals per width. This turns into a pattern of overlapping torn paper-like scales where the scale margins are consistently 10 microns apart. There are several of these scales per width of the fiber. (ASM #1)

UNDERFUR

Length: 10mm (Adorjan and Kolenosky 1969), 5-10mm (ASM #1 back), 5-7mm (ASM #1 tail)

Diameter Range: 12.5 microns (ASM#1 chin), 12 microns (ASM #1 butt)

Medullary Index: N/A

Medulla: No medulla

Color: Streaky reddish-brown.  Adorjan and Kolenosky (1969) says the underfur should be whitish-grey near the base and then darker near the tip.

Scales: petal-like

Macro Qualities: 2.9 – 4.5 feet long. Dark brown coat with silvery sheen at the throat (Forsyth 1999).  40-60” long.  Prime river otter fur is black-brown with belly slightly lighter and grayish chin and throat.  Longer guard hairs are often removed by furriers. (ADF&G 2008)  The North American otter is Lutra Canadensis and the Pacific North American otters are the least silky of them. After the first warm spell of the spring, tips of guard hairs might turn over or look singey.  Must be plucked to be marketable.  Middle and base sections of the fur are pale gray, but cannot be seen unless the fur is forceably spread apart.  Alaska Coast pelts are traditionally scraped clean and not semidressed by brain tanning as is done in Eastern Canada  Good “serviceability” (Bachrach 1953).

Cultures:

Notes: ASM #1 is from a full pelt the ASM education collection.  River otter fur is half as dense as sea otter fur, can be erected to increase insulation when out of the water.  Underfur is wavy to trap air and keep water from contacting the skin. (Mary Willson, “Despite Obstacles, Alaska Weasels Thrive.” Juneau Empire, Feb 5 2010).

Troubleshooting: Broad distal shield, basal petal-shaped hair pattern on both guard and overhairs is also seen in other mustelids, but otter hair is longer and wider (Teerink 1991).  Mayer 1952: “Distal spatulate tip is three times the width of the stalk on which it is borne.”  For the sea otter, he says the tip is less than twice the width of the stalk.  Have narrow medulla like the fur seals and sea lions, but otters have a wider medulla near the tip.??  (Mayer 1952).  This shield can be helpful in distinguishing between the otters.  A sea otter has a shield less than twice as wide as the stalk, but the river otter shield is typically 3X as wide as its stalk..  Sea otter has a very narrow medulla compared to any other weasel, under 0.3 and sometimes even narrower, and often interrupted.  River otter medullary index is usually around 0.48.  If only underfur is available, the otters and fur seal are difficult to distinguish.  All have pointed petal scales, no medulla, and similar width, although fur seal underfur has more of the wider hairs in the 15 micron range.  Underfur length may be helpful, as fur seal rarely exceeds about 18mm while sea otter may reach 25mm and river otter rarely exceeds 10mm.  River otter has less pigment in the underfur than sea otter or fur seal.

Range: Throughout Alaska except for Aleutian Islands, offshore islands of the Bering Sea (ADF&G 2008).

Names: Family Mustelidae (the mustelids)  Also called Northern River Otter or Land Otter.  There is another river otter in south America?  Beware, some say Lutra is a different genus from Londra/Lontra and usually refers to the Eurasian River Otter?  Might differ from sea otter in the presence of medulla in the guard hair and the lack of pigment in the underfur??  That is Brown’s (1942) take on Lutra.  But then Mayer (1952) mentions Lutra Canadensis, so how could we have a European Canadian otter??  Rearden (1981), Tumlison (1983), Forsyth (1999) also all say  “Lutra Canadensis.”  Londra Canadensis was used by ADF&G until most recent revision and now they are going with Lutra Canadensis. Lutra lutra is the Eurasian otter, which is sort of a river otter.

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