Northern river otters have often been blamed for serious depredation of game
fish, particularly trout. Food habit studies, however, have all
indicated that the bulk of the northern river otter diet consists of nongame fish
species. In many circumstances, northern river otters are beneficial to game
fish populations because they remove nongame fish that would otherwise
compete with game fish for food [
4]. Northern river otters, however, may
occasionally cause severe depredation in fish hatcheries [
1,
4].
Northern river otters have been extirpated or reduced in many areas due to human
encroachment, habitat destruction, and overharvest [
8]. Northern river otters
are relatively abundant in major nonpolluted river systems and in the
lakes and tributaries that feed them. They are scarce, however, in
heavily settled areas, particularly if the waterways are polluted. In
Maryland, no northern river otters occur in waters altered by acidic mine
drainages. The disappearance of northern river otters from West Virginia and
parts of Tennessee and Kentucky has been attributed to increased acidity
of ground water due to mining operations [
4]. Little research has been
done in evaluating the range of water quality that otters will tolerate
[
4]
The most readily apparent human impact on northern river otters results from
trappers harvesting otters for their fur. The northern river otter has been an
economically important furbearing species since Europeans first arrived
in North America [
4]. Habitat destruction has also resulted in a
decline in northern river otter populations. Some causes of northern river otter habitat
destruction include the development of waterways for economic or
recreational purposes, destruction of riparian habitat for homesites or
farmland, and a decline in water quality because of increased siltation
and/or pesticide residues in runoff [
4,
6,
16]. Pesticide residues
including mercury, DDT and its metabolites, and Mirex have been reported
in northern river otter tissues [
4].
Roads and railroad tracks that parallel or cross streams are probably
responsible for a considerable number of northern river otter deaths each year.
This is an important consideration in mountainous states where roads are
constructed along stream courses [
14].
Several researchers have associated good northern river otter habitat with the
activities of beavers. Northern river otter population dynamics may be
influenced not only by beaver trapping but also by wide fluctuations in
beaver numbers and subsequent habitat changes. In the western United
States, with its widely separated waterways and large variations in
flow, beaver-created habitat may be critical to northern river otter denning and
foraging [
6].
A variety of internal parasites affect northern river otters. Of these, two
roundworms (Stronguloides lutrae and Gnathostoma miyazakii) may cause
serious pathological damage. Northern river otters are also susceptible to
canine distemper, jaundice, hepatitis, and feline panleucopenia [
4].
In recent years several states have transplanted northern river otters in an
attempt to establish or reestablish breeding populations [
17].
