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"Jay DeLong" <jdelong at nwifc_wa.gov>: NANFA-- flathead cat introduction effects

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From: "Jay DeLong" <jdelong at nwifc_wa.gov>
To: nanfa at aquaria_net
Subject: NANFA-- flathead cat introduction effects
Date: Sun, 26 Oct 1997 08:43:52 +0000
Message-ID: <199710261645.IAA21205 at chinook_nwifc.wa.gov>

Hi all.  This is from the Nature Conservancy.  

Jay DeLong


Not all destructive alien species come from distant lands. The
flathead catfish (Pylodictis olivaris) poses no threat within its
native range of the lower Great Lakes, Mississippi River basin, and
parts of the Gulf slope drainage. But when introduced to new waters as
a sportfish, it's a different story. Now found in the rivers and
reservoirs of 18 states where it was previously unknown, this catfish
is depleting native fish populations. 

The flathead has earned a reputation as an outstanding sportfish. It
lives for 20 years or more and reaches a length of four feet and a
weight of 50 pounds. Its attractiveness to fishermen has encouraged
its introduction into other drainages in the West and Southeast. Good
sportfish or not, its appearance in these river systems had unforeseen
and disastrous effects on native fishes. 

Unlike other catfishes, the flathead is not a scavenger; as an adult,
it feeds chiefly on other fish. A voracious predator, it has sped to
the top of the food chain in aquatic communities where it has been
introduced. In 1966, 11 adult flatheads were released in North
Carolina's Cape Fear River. From a single point introduction they
proliferated along a 150-mile stretch of river. Within 15 years,
flatheads became the dominant predator there, feasting on bullheads
(Ictalurus spp.). And after these were wiped out, they shifted to
commercially valuable American shad (Alosa sapidissima). Today,
flathead catfishes constitute more than 10 percent of the river
system's fish by number, and 65 percent by weight. Similarly, the
flathead is seriously affecting the fish fauna of the Apalachicola
River in Florida, where it consumes the young of the federally listed
threatened Gulf sturgeon (Acipenser oxyrhynchus desotoi). 

Introduced into Arizona's Salt River in 1967, the flathead reproduced
rapidly within the first decade, while populations of native fishes
plummeted. Here, the foreigner defeated repeated attempts to
reintroduce both the endangered razorback sucker (Xyrauchen texanus)
and the endangered Colorado squawfish (Ptychocheilus lucius). It preys
on the imperiled species' young. 

Because of the catfish's threat to the recovery of the Colorado
squawfish and other endangered fishes, a new federal/state agreement
prohibits introduction of the species in the upper Colorado River
basin. This agreement, which the Conservancy helped negotiate, also
bans the introduction of eight other non-native fishes. Although the
agreement is sensitive to traditional sportfishing management by state
agencies, it provides for careful review of continued stocking of
several non-native fishes whose release is not prohibited altogether.
And, as part of a comprehensive recovery program for the system's
endangered native fish species, a number of cooperative federal/state
actions will focus on removing or controlling non-native fishes
already present in the upper Colorado River basin.

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