Adult American shad migrating upriver through Bonneville Dam

on the Columbia River

American shad (Alosa s

are known to anglers for not giving

up easily when hooked. Altho

they only reach an average of 3 to 

5 pounds, they fight like a larger 

fish. Shad also have fought their 

way into waters of the West Coast

of North America with great

success. The native habitat of 

American shad is the East Coast, 

although the population has 

plummeted due to overfishing and

development. Conversely, 

numbers of introduced American 

shad on the West Coast have 

increased greatly in the last 50 

years. Adult shad migrate up 

coastal rivers to spawn, and 

apidissima) 

ugh 

une,

picatum

the resulting young 

shad return to the 

sea after several months 

in freshwater. In the 

Columbia River, over 5 

million migrating adults 

were counted during 

2004 at Bonneville Dam

in Oregon and Washington State. 

Furthermore, in the lower river, 

young shad are one of the most 

abundant larval and juvenile fishes. 

The introduction of American shad 

to the West occurred in 1871. 

Because of shad’s value as food fish 

in the East, the California Fish 

Commission requested that Seth 

Green, an enterprising fish culturist, 

transport shad to the Sacramento 

River. During the hot month of J

Green used the recently-completed 

transcontinental railway to move 

12,000 small shad across the 

country in 7 days. Young shad were 

in four 8-gal milk cans, and Green 

made stops along the way for fresh 

water and cooling ice. The 

transplanted fry survived, and the 

population grew. Shad migrated out 

of the Sacramento River into the 

Pacific Ocean, soon becoming 

established up and down the coast. 

The effects of the high numbers of 

young and adult American shad on 

the ecosystem of the West Coast are 

largely unknown. Shad compete 

with native and introduced fishes for 

food and habitat. Fishery biologists 

are particularly concerned how this 

may be affecting endangered 

salmonid populations. However, 

more research is necessary to 

understand the role of shad in the 

western aquatic community. 

Eurasian Watermilfoil 

Standing on a bluff overlooking the 

Columbia River you can see large 

dark patches in the water. This is an 

aquatic weed called Eurasian 

watermilfoil (Myriophyllum s

L.) that is native to Europe and Asia 

Aquatic Invasive Species

Counts of adult American 

shad and salmon migrating 

upriver through Bonneville 

Dam during 2001

USGS

U.S. Department of the Interior USGS FS 2006-3069 

U.S. Geological Survey August 11, 2005 

Invasive species are plants or animals that are 

present in an ecosystem beyond their native range. 

They may have few natural controls in their new

environment and proliferate. They can threaten 

native species and interfere with human activities. 

The Western Fisheries Research Center (WFRC) 

has been conducting research to understand how

non-native species invade and affect ecosystems, 

thus aiding management efforts. 

An Invader From the East Coast
Water is pumped into vast tanks to stabilize a vessel, and later the 

ballast water is discharged. In this way, animals and plants can be 

transported thousands of kilometers from their native habitats and 

deposted in a new environment.

The aquarium strain of Caulerpa taxifolia 

(C. taxifolia) is an extremely invasive

seaweed that has the ability to form a

dense carpet on almost any surface. 

The European Green Crab (Carcinus 

maenas) is highly adaptable, competing 

with and displacing native crabs.

Spartina (Spartina alterniflora, S. 

anglica) is a grass capable of taking 

over large estuarine areas in the coastal 

marine zone.

The burrowing activities of the Chinese 

mitten crab (Eriocheir sinensis) can 

cause shore erosion. To invade a new 

river system they may leave the water 

and cross dry land. 

For additional information, please 

contact: 

Lyman Thorsteinson, Center Director 

U.S. Geological Survey

Western Fisheries Research Center 

6505 NE 65th Street 

Seattle, WA 98115 

Phone: (206) 526-6282 

 FAX (206) 526-6654 

http://wfrc.usgs.gov

The Zebra mussel

(Dreissena polymorpha) 

is a rapidly growing 

invasive species that 

causes severe fouling 

problems such as 

clogging intake pipes,

damaging boat hulls, and 

interfering with the 

operation of locks and 

dams.

Today there are more than 45,000 

commercial cargo-carrying vessels that 

use ballast water to maintain stability

when cargo loads vary. 

One ship may contain more than 12 

million gallons of ballast water providing 

a very efficient vector for aquatic 

microbes, plants, and animals. In fact, it 

is estimated that 7,000 different species

are transported around the world daily in

ballast water. Therefore, there is a 

critical need to develop tools to detect 

and eradicate invasive species in ballast 

water prior to their release and 

establishment in coastal ecosystems. At

WFRC, scientists are working to develop 

DNA markers to detect and monitor 

invasive species in ballast water and 

evaluate oceanic exchange. Using stateof-the-art technology, we are developing 

diagnostic systems to allow as many as 

20,000 species to be detected at one time. 

This technology will allow state and 

federal agencies to monitor how clean 

ballast water is before it is dumped in 

coastal ports. 

 

and has spread dramatically. 

Scientists are not really sure what 

effect the Eurasian watermilfoil is 

having on the Columbia River 

ecosystem. One thing is for sure, 

however, the aquatic weed is 

affecting recreational opportunities 

for boaters, anglers, swimmers, a

windsurfers. Eurasian wate

forms dense mats that can clog 

boat motors and make swimming

difficult. 

nd

rmilfoil 

The WFRC has initiated efforts to 

help understand the economic and 

biological effects of Eurasian 

watermilfoil. The first step is to 

document the extent of this aquatic 

weed in the Columbia River. The 

WFRC has conducted surveys of

the weed and the river bottom. We 

are using this data to develop 

models that will predict what is 

promoting or limiting Eurasian

watermilfoil in the Columbia 

River. These models can then be 

used to help formulate 

management plans for mitigating 

this aquatic invader. 

Ballast Water 

Although there are several vectors 

for invasive marine species such as 

aquaculture, recreational boats, and 

public aquaria, the most important 

transportation vector is ballast 

water carried in commercial ships.

Eurasian watermilfoil in the Columbia River