Transcript (W) of northern snakeheads sampled in the Potomac

Biological Taxonomy
Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Family: Channidae
Species: Channa argus
Common name: Northern Snakehead
Background & Environmental Constraints
 Origin: China, eastern Russia, and the Korean
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peninsula
Speciation: Channa argus is 1 of 29 snakehead
species
Temperament: Aggressive
Maximum size: Up to 5 feet long
Water parameters:
 Freshwater
 pH: 6.0 - 7.5
 Temperature: 72-82˚ F (22-28˚C)
Threat to Biodiversity & Economy
 This top level predator fish is known to survive on land and
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cause major strain on local ecosystems
Alter freshwater ecosystems by competing against native fish
Reduce biodiversity through predation on aquatic and
terrestrial species
Could push endangered or threatened species to the brink of
extinction
May introduce fungal pathogen known as Epizootic
Ulcerative Syndrome (EUS) – infects foreign freshwater fish
Could damage commercial and recreational fishing industry
in the Chesapeake by diminishing populations of fish that
spawn in the Potomac River
Millions of dollars have been spent on fish stocking, dam
modifications, and other projects to limit snakehead impact
Introduction to U.S. Waters
 In the past, Asian markets and other grocers were allowed to
import living snakeheads to the U.S.
 Over time, human beings introduced the species to native waters
 First reported in U.S. waters in 1977 in Silverwood Lake, California
 National Media debut in 2002
 An angler caught an unfamiliar fish that measured 28 inches
from a pond in Crofton, Maryland.
 Took the picture to Maryland Dept. of Natural Resources
where it was later identified.
 After another fisherman caught spawning adult and baby
snakeheads from the same pond, the national media
disseminated the first stories of the snakehead.
 To prevent the fish from migrating to the Potomac River,
Maryland wildlife officials dumped the pesticide, Rotenone.
 Killed all fish, including 6 adult and over 1000 snakehead
young.
 An unsuccessful effort as Channa argus appeared in the
Potomac River 2 years later.
Northern Snakehead possesses competitive advantages
that may allow it to out-compete native fish species
 Primitive lungs
Sacs above each gill that can fill with air and draw oxygen from the
stored air.
 Allows it to survive waters that are low in oxygen.
 Allows it to survive out of water for 2 – 3 days.
 Allows it to live under a sheet of ice
 Aggressive
 Both parents guard the eggs and the fry
 Known to attack fishing lures.
 Highly prolific
 Spawning females can release up to 15,000 eggs at a time
 Can mate up to 5 times per year.
 Equates to 75,000 offspring per year.
 Indiscriminate feeders
 Feed on native fish, amphibians, crustaceans, birds, small reptiles and
small mammals.
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 Snakehead video
Purpose:
In 2004, the VA Dept. of Game and
Inland Fisheries initiated a study to
monitor the snakehead’s expansion in
the Potomac from 2004–2006.
Methods:
 Surveyed on a monthly basis:
Areas of known snakehead concentrations.
 Bodies of water contiguous but farther away to assess range.
Relative abundance of snakeheads was based on the number of fish retrieved per
hour of electrofishing, and catches per unit effort of angling.
 Explanation of electrofishing
Sampled fish were separated into 8 groups, ages 0-7 (approximated based on size of
sagittal otolith at necropsy).
 Accumulates in rings as it grows
 Used in age or growth studies
Counts of daily rings on sagittal otoliths of newborns (age-0) were used to estimate
when fish hatched.
Data collection included total length (mm), weight (g), stomach content evaluation,
gonad condition, and length at age.
 Stomach content evaluation entailed only removal and identification.
 Gonadosomatic indices (GSI) of ovary weight to body weight was used to quantify
spawning period.
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Results:
Table 1. Total number of northern snakeheads captured
from the Potomac River system, Virginia, during 2004-2006
by use of several gear types (HL = hook and line; EP =
electrofishing; BP = Backpack; other = dip net, trap net,
seine, standing, and bow angling).
Year
2004
2005
2006
Total
HL Boat EF BP EF
13
4
0
11
59
127
24
171
11
48
234
138
Barge EF Other
0
3
71
3
1
7
72
13
Total
20
271
214
505
Table 2. Mean total length (TL) and weight (W) of
northern snakeheads sampled in the Potomac River
system, Virginia, during 2004-2006.
TL (mm)
Year
2004
2005
2006
N
20
270
215
Mean
406
273
475
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SD
105
120
146
Min. Max.
88
634
113
655
164 765
Table 3. Length-at-age data (mm) for 167 northern
snakeheads sampled in the Potomac River system,
Virginia, during 2004-2006 (all years combined).
Age
0
1
2
3
4
5
6
7
W (g)___________
N Mean Min. Max.
782 553 7
2635
493 621 13 3145
1381 1009 36 4598
N
9
18
24
53
39
17
4
3
TL mean
133
190
287
357
431
545
578
560
SD
23
20
85
85
100
111
52
9
Min.
88
155
163
218
308
362
531
531
Max.
166
227
480
588
669
674
634
569
Table 4. Frequency of occurrence (percentage of stomachs containing the
taxon) of identifiable taxa consumed by 219 northern snakeheads
collected in the Potomac River system, Virginia, during 2004-2006.
Common name
 Banded killifish
 White perch
 Pumpkinseed
 Bluegill L.
 Goldfish
 Gizzard shad
 American eel
 Yellow perch
 Largemouth Bass
 Sponail shiner
 Eastern silvery minnow
 Mummichog
 Channel catfish
 Green sunfish
 Tessellated darter
 Frog
 Crayfish
Scientific name
Fundulus diaphanus
Morone americana
Lepomis gibbosus
macrochirus
Carassius auratus
Dorosoma petenense
Anguilla rostrata
Perca flavescens
Microplevus salmoides
Notropis hudsonius
Hybognathus regius
F. heteroclitus
Ictalurus punctatus
L. cyanellus
Etheostoma olmstedi
Rana spp.
Cambaridae
Frequency (%)
27
5
5
5
2
1
1
1
1
1
<1
<1
<1
<1
<1
<1
<1
Conclusions:
 Dramatic increase in catch rates suggests an overall
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increase in snakehead population, although an increase
in electrofishing capture efficiency could have added
some degree of bias.
Maximum size, including total length and weight,
increased every year, which suggests that the population
matured.
17 species were identified in stomach contents.
Female Gonadosomatic Indices rose in early April,
peaked in June, and diminished through September.
Counts of daily rings on otoliths of newborns indicated
hatching from mid-June to early September.
Implications:
 Despite the apparent increase in snakehead population, the
area of colonization did not appear to increase over the
original 23-km main stem of the Potomac.
 Yearly increase in maximum size is consistent w/ theory that
the population was recently established.
 Stomach contents consistent w/ theory that snakehead is
piscivorous and opportunistic in feeding (ie. Frog, crayfish).
 Female GSIs, estimated hatch dates, and the discovery of a
nest in early September, indicate a spawning period of at least
5 months in the Potomac.
Works Cited:
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Virginia Invasive Species Council. 2005. Virginia Invasive Species Management Plan. Virginia
Department of Conservation and Recreation Division of Natural Heritage. Richmond. 84 p.
Invasive Species. 2004. Marek Topoleski, Mary Fabrizio, Ron Lauda. Pg 77-122.
Aquatic Community. Northern Snakehead. 2004. Retrieved on Oct. 26, 2009.
<http://www.aquaticcommunity.com/channa/argus.php>.
Odenkirk, John, and Steve Owens. Expansion of a Northern Snakehead Population in the Potomac
River System. American Fisheries Society 136:1633-1639, 2007.
The Environmental Literacy Council. Snakeehead Fish.. 2008. Retrived on Oct. 25, 2009.
< http://www.enviroliteracy.org/article.php/1473.html >.