7605

• UCREFRP Catalog Number: 7605
• Author: Schaeffer, L.
• Title: Avian Predators at ODFW Hatcheries
• USFW Year: 1992.
• USFW - Doc Type: Their Identification and Control.
• Copyright Material: YES

operation of the device, the more effective it is. The most
effective frightening device is increased human presence, which
can also be the most costly. Control measures must take into
account the type of predator they will be used against. Some
measures are useful for a wide range of pests and others are
useful only for specific types.

Physical Devices

Physical devices can be designed for specific types of
predators. If the predominant loss has occurred from wading
birds such as herons, electric fences or low level netting are
effective deterrents. Some hatcheries have been successful in
deterring herons by lowering the pond water level so that the
birds cannot reach the fish. Ponds at Roaring River Hatchery
have vertical walls with undermined walkways, these coupled with
water level manipulations prohibit the birds from perching on the
walls or wading into the ponds and reaching the fish.

Where predators attack fish by diving from the air or from a
perch, lines or wires placed over the tops of ponds are
effective. These devices break up the flight pattern, although
occasionally a bird is killed by the lines.

Cormorants are difficult to keep away from large ponds.
They have been known to swim under netting suspended at or below
the water surface to get to fish. At Wahkeena Pond, losses were
so high that netting was placed several feet below the surface of
the water to give the fish protection.

Physical control measures must be designed specifically for
the hatchery as well as for the predator. Some hatcheries must
conform to standards established by a local authority. Wahkeena
Pond, in the Columbia Rive~ Gorge, must meet aesthetic
requirements for physical structures because this area has been
designated as a national scenic area. The netting and posts used
at Wahkeena Pond were designed for minimal visual impact.
Hatcheries must design their predator control devices to avoid
creating hazards and nuisances for their workers and for
visitors. New hatchery designs such as those at Irrigon and the
new umatilla Hatchery take these aspects of protection from avian
predators into consideration.

The physical barriers presently being used at ODFW fish
rearing facilities include:

1. Netting, screen, lines, or wire fences on the sides or the
top of ponds.

2. Solid pond roof-covers.

3. Total enclosure of ponds with either netting or solid
walls.

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