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RIVER OTTERS

Edward P. Hill

Chief, Bird Control Research S ection

Denver Wildlife Research Center

USDA-APHIS-ADC

Denver, Colorado 80225

Damage Prevention and

Control Methods

Exclusion

Fence small raceways, tanks, or ponds

with 3 x 3-inch (7.6 x 7.6-cm) mesh

wire.

Repellents

None are registered.

Toxicants

None are registered.

Fumigants

None are registered.

Trapping

Use Conibear® traps (Nos. 220 and

330), foothold traps (No. 2), and

snares to control river otters in

damage situations.

For restocking purposes, river otters

can be caught in live traps, modified

No. 1 1/2 soft-catch traps, and No.

11 longspring traps.

Shooting

If nonlethal approaches cannot be em-

ployed, shooting with shotgun or

small-caliber rifle can be effective in

damage situations that involve only

one or two otters.

Fig. 1. The North American river otter, Lutra

canadensis

Identification

River otters (Lutra canadensis, Fig. 1)

are best known for their continuous

and playful behavior, their aesthetic

value, and the value of their durable,

high-quality fur. They have long,

streamlined bodies, short legs, and a

robust, tapered tail, all of which are

well adapted to their mostly aquatic

habitat. They have prominent whiskers

just behind and below the nose, thick

muscular necks and shoulders, and

feet that are webbed between the toes.

Their short but thick, soft fur is brown

to almost black except on the chin,

throat, cheeks, chest, and occasionally

PREVENTION AND CONTROL OF WILDLIFE DAMAGE — 1994

Coop erat ive Extension Division

Institute of Agriculture and Natural Resources

University of Nebraska - Lincoln

United States Department of Agriculture

Animal and Plant Health Inspection Service

Animal Damage Control

Great Plains Agricultural Council

Wildlife Committee

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the belly, where it is usually lighter,

varying from brown to almost beige.

Adult males usually attain lengths of

nearly 48 inches (122 cm) and weights

of about 25 pounds (11.3 kg), but may

reach 54 inches (137 cm) and 33

pounds (15 kg). Their sex can be

readily distinguished by the presence

of a baculum (penile bone). Females

have 4 mammae on the upper chest

and are slightly smaller than males.

Female adults measure about 44 inches

(112 cm) and weigh 19 pounds (8.6 kg).

The mean weights and sizes of river

otters in southern latitudes tend to be

lower than those in latitudes farther

north.

Range and Habitat

River otters occur throughout North

America except the arctic slopes, the

arid portions of the Southwest, and the

intensive agricultural and industrial-

ized areas of the midwestern United

States (Fig. 2). Their precolonial range

apparently included all of North

America except the arid Southwest

and the northernmost portions of

Alaska and Canada. Otter populations

are confined to water courses, lakes,

and wetlands, and therefore, popula-

tion densities are lower than those of

terrestrial species. Their extirpation

from many areas is believed to have

been related more to poisoning by pes-

ticides bio-magnified in fishes, and to

the indirect adverse effects of water

pollution on fish, their main food, than

to excessive harvest. The loss of ponds

and other wetland habitat that resulted

from the extirpation of beaver in the

late 1800s may have adversely affected

continental populations of river otters

more than any other factor. Increases

in the range and numbers of river

otters in response to the return of bea-

ver has been dramatic, particularly in

the southeastern United States. Recent

releases totaling more than 1,000 otters

have been made in Arizona, Colorado,

Iowa, Kansas, Kentucky, Missouri,

Nebraska, Oklahoma, Pennsylvania,

Tennessee, and West Virginia in efforts

to reestablish local p opulations.

River otters are almost invariably asso-

ciated with water (fresh, brackish, and

salt water), although they may travel

overland for considerable distances.

They inhabit lakes, rivers, streams,

bays, estuaries, and associated riparian

habitats. They occur at much higher

densities in regions of the Great Lakes,

in brackish marshes and inlets, and in

other coastal habitats than farther

inland. In colder climates, otters fre-

quent rapids and waterfall areas that

remain ice-free. Vegetative cover and

altitude do not appear to influence the

river otter’s distribution as much as do

good or adequate water quality, the

availability of forage fish, and suitable

denning sites.

Food Habits

The diet of the river otter throughout

its range is primarily fish. Numerous

species and varieties of fresh and

anadromous fishes are eaten, but shell-

fish, crayfish, amphibians, and reptiles

are also frequently eaten, as are several

species of crabs in coastal marshes.

Mammals and birds are rarely eaten.

Consumption of game fishes in com-

parison to nongame (rough) fishes is

generally in proportion to the diffi-

culty, or ease, with which they can be

caught. Because of the availability of

abundant alternate food species in

warm water, losses of the warm water

sport fishes are believed minor com-

pared to losses river otters can inflict

on cold water species such as trout

and salmon.

General Biology,

Reproduction, and

Behavior

The reproductive biology of river

otters and all other weasels is complex

because of a characteristic known as

delayed implantation. Following

breeding and fertilization in spring,

eggs (blastocysts) exist in a free-

floating state until the following winter

or early spring. Once they implant,

fetal growth lasts 60 to 65 days until

the kits are born, usually in spring

(March through M ay) in most areas. In

the southern portion of the range the

dates of birth occur earlier, mostly in

January and February, implying

implantation in November and

December. Litters usually contain 2 to

4 kits, and the female alone cares for

the young. They usually remain

together as a family group though the

fall and into the winter months. Sexual

maturity in young is believed to occur

at about 2 years of age in females, but

later in males.

River otters are chiefly nocturnal, but

they frequently are active during day-

light hours in undisturbed areas.

Socially, the basic group is the female

and her offspring. They spend much of

their time feeding and at what appears

to be group play, repeatedly sliding

down steep banks of mud or snow.

They habitually use specific sites

(toilets) for defecation. Their vocaliza-

tions include chirps, grunts, and loud

piercing screams. They are powerful

swimmers and are continuously

active, alert, and quick—characteristics

that give them immense aesthetic and

recreational value. Their webbed feet,

streamlined bodies, and long, tapered

tails enable them to move through

water with agility, grace, and speed.

Seasonally, they may travel distances

of 50 to 60 miles (80 to 96 km) along

streams or lake shores, and their home

ranges may be as large as 60 square

miles (155 km

2

). Males have been

recorded to travel up to 10 miles (16

km) in 1 night.

River otters use a variety of denning

sites that seem to be selected based on

availability and convenience. Hollow

Fig. 2. Distribution of the river otter in North

America.

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logs, rock crevices, nutria houses, and

abandoned beaver lodges and bank

dens are used. They will also frequent

unused or abandoned human struc-

tures or shelters. Natal dens tend to be

located on small headwater branches

or streams leading to major drainages

or lakes.

Damage and Damage

Identification

The presence of river otter(s) around

or in a fish hatchery, aqu aculture, or

fish culture facility is a good indication

that a damage problem is imminent.

Otter scats or toilets that contain

scales, exoskeletons, and other body

parts of the species being produced is

additional evidence that damage is on-

going. Uneaten parts of fish in shallow

water and along the shore is evidence

that fish are being taken. Otters usually

eat all of a small catfish excep t for the

head and major spines, whereas small

trout, salmon, and many of the scaled

fishes may be totally eaten. Uneaten

carcasses with large puncture holes are

likely attributable to herons. River

otters can occasionally cause substan-

tial damage to concentrations of fishes

in marine aquaculture facilities. Often

the damage involves learned feeding

behavior by one or a family of otters.

Legal Status

The river otter is listed in Appendix II

of the Convention on International

Trade in Endangered Species of Flora

and Fauna (CITES). Its inclusion in this

appendix subjects it to international

restrictions and state/province export

quotas because of its resemblance to

the European Otter. Moreover, the

river otter is totally protected in 17

states. Twenty-seven states have trap-

ping seasons, and four states and two

provinces have hunting seasons.

Damage Prevention and

Control Methods

Because river otter damage has been

minor compared to that of other spe-

cies, and because of its legal status

under the CITES Agreement, little con-

trol research and experimentation has

been done. Registration of repellents,

toxicants, or fumigants for river otter

control has not been sought. Alternate

aquacultural practices and species,

predator avoidance behavior, and use

of protective habitat have not been

fully explored. Careful assessment

should be made of reported damage to

determine if nonlethal preventative

measures can be employed, and to

ensure that if any lethal corrective

measures are employed, they do not

violate state or federal laws. Damage

problems should then be approached

on an individual basis. Cultural meth-

ods and habitat modification are nor-

mally not applicable. Opp ortunities to

use repellents, toxicants, fumigants,

and frightening devices are infrequent,

yet the development of any of these or

other effective nonlethal approaches

would be preferable to lethal control

measures.

Exclusion

Fencing with 3 x 3-inch (7.6 x 7.6-cm)

or smaller mesh wire can be an eco-

nomically effective method of prevent-

ing damage at aquacultural sites that

are relatively small, or where fish or

aquaculture activities are concentrated.

Fencing is more economical for protec-

tion of small areas where research,

experimental, or propagation facilities

such as raceways, tanks, ponds, or

other fac ilities hold concentrations of

fish. Hog wire-type fences have also

been used effectively, but these should

be checked occasionally to ensure that

the lower meshes have not been

spread apart or raised to allow otters

to enter.

Electric fences have also been used,

but they require frequent insp ection

and maintenance, and like other fenc-

ing, are usually impractical for protect-

ing individual small ponds, raceways,

or tanks in a series. They are of greater

utility as a supplement to perimeter

fences surrounding an aquaculture

facility.

Trapping

Traps that have been used effectively

for river otters include the Conibear®

(sizes 220 and 330) or other similar

body-grip ping traps and leghold traps

(modified No. 1 1/2 soft-catch and No.

11 double longspring). The latter two

are usually employed to capture river

otters for restocking purposes. In

water, body-gripping traps are usually

placed beneath the water surface or

partially submerged where runs

become narrow or restricted (Fig. 3).

They are effective when partially sub-

merged at dam crossings, the main

runs in beaver ponds, or other loca-

tions where otters frequently leave the

water. Body-gripping traps are also

effective in otter trails that connect

pools of water or that cross small pen-

insulas. In these sets, the trap should

Fig. 3. Body-gripping trap suspended with a pole thro ugh the spring loops in a channel set to cap-

ture a river otter.

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Shooting

Shooting the offending otters that

cause damage problems will often

effectively prevent continued losses.

Although otters are shy, they are

inquisitive and will often swim within

close range of a small rifle or shotgun.

Extreme caution should be taken to

avoid ricochet when shooting a rifle at

objects surrounded by water.

Shooting river otters for fur harvest is

legal in four states and one Canadian

province. Check your local, state, and

federal laws and permits governing

shooting, the use of lights after dark,

the seasons, and the possession of otter

carcasses or parts, to ensure that

planned activities are legal.

Economics of Damage

and Control

Although individual incidences of

river otter damage and predation on

fish can cause substantial losses to

pond owners and to fresh water and

marine aquacultural interests, their to-

tal effects are believed to be insignifi-

cant. Given the otter’s aesthetic and

recreational value, and its current legal

status, consideration of broad control

programs are unwarranted and

undesirable.

Acknowledgments

Figure 1 from Schwartz and Schwartz (1981).

Figure 2 from Toweill and Tabor (1982), adapted

by Dave Thornhill, University of Nebraska-

Lincoln.

Figure 3 by Clint Chapman, University of

Nebraska-Lincoln.

For Additional

Information

Hill, E. P. 1983. River otter (Lutra canadensis)

Pages 176-181 in E. F. Deems Jr. and D.

Pursley eds. North American furbearers, a

contemporary reference. Internat. Assoc.

Fish Wildl. Agencies and Maryland Dep.

Nat. Resour.

Hill, E.P., and V. Lauhachinda. 1980.

Reproduction in river otters from Alabama

and Georgia. Pages 478-486 in J. A. Chapman

and D. Pursley eds., Proc. worldwide

furbearer conf. Maryland Dep. Nat. Resour.,

Annapolis.

Melquist, W. E., and Ana E. Dronkert 1987.

River otter. Pages 626-641 in M. Novak, J. A.

Baker, M. E. Obbard, and B. Malloch eds.

Wild furbearer management and

conservation in North America. Ontario

Minister of Nat. Resour., Toronto.

Toweill, D. E., and J. E. Tabor. 1982. River otter.

Pages 688-703 in J. A. Chapman and G. A.

Feldhamer eds. Wild mammals of North

America: biolo gy, management, and

economics. The Johns Hopkins Univ. Press.,

Baltimore, Maryland.

Editors

Scott E. Hygnstrom

Robert M. Timm

Gary E. Larson

be placed at a height to blend with the

surrounding vegetation to catch an

otter that is running or sliding. After

ice forms on the surface of streams and

lakes, some trappers bait the triggers

of body-gripping traps with whole

fish. River otter trapping is prohibited

in 21 states and one Canadian prov-

ince. Check local regulations before

trapping.

Most of the wild otters used for

restocking in recent years were caught

with No. 11 longspring traps in coastal

Louisiana. These animals were usually

caught in sets for nutria, in traps that

were set in narrow trails and pullouts

where shallow water necessitated that

otters walk rather than swim. Leghold

traps are also effective when placed in

shallow edges of trails leading to otter

toilets or other areas they frequent.

Leghold traps set in out-of-water trails

and peninsula crossings should be

covered with damp leaves or other

suitable covering.

With the depression of fur prices, nui-

sance beaver problems and efforts to

control them have increased substan-

tially throughout the United States.

The killing of otters during beaver con-

trol trapping can be minimized by

using snares, but they do occasionally

sustain moderate injuries. In most situ-

ations, snared river otters can be

released unharmed. Accordingly,

snares are neither the most effective,

nor the most convenient devices for

capturing river otters or removing

them from an area, and therefore are

not recommended for either.