The Introduced Species Problem

• Description: related to the Platte River Endangered Species Partnership ‎(aka Platte River Recovery Implementation Program or PRRIP)‎
• State: CO
• State: NE
• State: WY
• Basin: Statewide
• Water Division: 1
• Title: The Introduced Species Problem
• Water Supply Pro - Doc Type: Report/Study

There is a prevailing thought among management agencies that it is acceptable
to stock native fishes, predator or prey species, anywhere into the Missouri River
system. Presumably the rationale behind this notion is that all of the species evolved
together and have adaptations to tolerate interspecific interactions. However, the validity
of this notion must be called into question. Not only have historic habitats changed,
altering niches and straining long- established relationships, but the distinction between
native vs. nonnative fishes has become clouded by several issues:
(1). Some fishes (e.g. walleye) were stocked before studies demonstrating their
presence or absence were completed and there were some problems with
misidentification.
(2). Natural or "native" Missouri River habitats have been so heavily influenced by
anthropogenic changes that it is arguable whether any native habitats remain in the
mainstream river. Thus, from the standpoint of damage to listed or sensitive species, it
makes little difference whether a nonnative fish is stocked into a native habitat, or a
native fish is introduced into a "nonnative" habitat.
(3). In the historic river, a mix of complex riverine habitats occurred and different
conditions supported different species. For example, centrarchids were adapted to
quiet, clear backwaters and oxbows, and chubs were adapted to the turbid conditions of
the fast flowing river channels. While "native" to a river reach, neither were "native" to
habitats used by the other.
(4). If biodiversity is to be maintained, management actions should be judged relative to
their affect on listed, rare, or declining native Missouri River fishes.
The notion that physical habitat changes caused the declines of native fishes, and
that introduced fishes have had little affect remains untested. There are no areas of the
Missouri River in which physical habitat changes have occurred without fish
introductions, whether intentional or nonintentional. However, it is clear that introduced
fishes have not benefitted native fish populations, and it is likely that declines of some of
the native fishes would not have been as precipitous if fish introductions had not
occurred. Additional fish introductions and management practices favoring the spread
and proliferation of introduced species will undoubtably harm the native fish fauna,
resulting in more listings of native fishes, and reducing the prospects for recovering
species that are listed now and will be listed in the future.
The consequences of introducing so many nonnative fishes into habitats where
they may compete with and prey upon native fish populations seems obvious in view of
the extensive body of knowledge that has accumulated in the past 15 years. There
remains a critical need for management agencies to recognize the potential problems of
fish introductions, to investigate these problems with well - planned research, to share
research findings in open forum with concerned agencies and individuals, and to
formulate appropriate management actions.
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