Transcript The Spread, Effect and Mitigation of Bullfrogs

The Spread, Effect and Mitigation of
Bullfrogs in the Western United
States
Jennifer Spawn
SWES 474
28 November 2006
The Origin of Bullfrogs
 Bullfrogs
 They

are originally native to Europe
were introduced to the Eastern U.S.
They are now considered “naturalized”
 West
of the Rocky Mountains they are still
considered non-native
Where art thou, Bullfrog?
 highly

aquatic, but will use the land
migration
 Found
in both lentic and lotic freshwater
environments
 Mainly temperate and subtropical species
 Like vegetation to hide in and lay eggs on
Ya’ll might make me act A’frog up in
here
 mostly
nocturnal but are somewhat active
during the day
 Males are territorial
 They will eat anything will fit in their
mouths…including small children and pets
 breathe through their skin
The Big, Bad Bullfrog
Bullfrogs have been in the West since the 1890’s
 They were introduced as a sport animal
 Because of their voracious appetite bullfrogs
have been labeled a nuisance

They are outcompeting the native
anuran populations
 With a decline in
anuran populations
already, natives are in
much greater danger

Are bullfrogs really that bad?





A study by Hecnar and M’Closkey
found a change in community
composition in SE Canada
As bullfrogs declined the native
species flourished
Interspecies competition was a
factor
A release of predation was found
to be the leading cause of native
species revival
This study is the general
consensus among biologists:
bullfrogs are a negative keystone
species in an ecosystem





A study done by Hayes and
Jennings indicates bullfrogs may
not be the cause
Habitat loss, fragmentation and
pollution may also be factors
Other predators may also be to
blame
Disease is also a major player
Bottom line we really don’t have a
clear answer…interspecific
relationships are complex
So what’s the deal here?
(Arizona)
 The
native Ranid species in Arizona are all
either threatened or are of special concern
 In many areas native species are in direct
competition with and predation by bullfrogs
 However to say bullfrogs are the sole
cause is irresponsible

Bullfrog populations are out of control in some
areas
What’s the government doing?

The U.S. Fish and Wildlife
Service is the main agency
dealing with bullfrog effects


ESA
The Arizona Game and Fish
Department also helps out


You can hunt bullfrogs if you
want!
www.azgfd.gov
Specific Mitigation
 Biological
 Chemical
 Mechanical
 Integrated
Pest Management
Biological Control
 As
of yet there is no really great biological
control of bullfrogs
 Large Mouth Bass, Diving beetles,
Dragonfly larvae and water nymphs like to
eat them

None species specific
 But
still, the bullfrog population is growing
rapidly in some areas of the state
Chemical Control
Rotenone
 Rotenone
is a chemical used primarily by
fisheries
 It does not allow cellular respiration



The electron transport chain is interrupted
Oxygen builds up in the blood and slows
breathing until the animal dies
Adult bullfrogs do not have gills but diffuse
oxygen across their skin…thus Rotenone
should have an affect on adult bullfrogs
HOWEVER…it
doesn’t !
Lessons from the San Rafael Valley

Rotenone was
applied to kill bullfrogs
 People were
positioned around the
tank to gig bullfrogs
as they left the water
 People were also
positioned to rescue
salamanders
Lessons from the San Rafael Valley

Rotenone although it breaks down by itself in
about a week, must be neutralized with
Potassium permanganate
Lessons from the San Rafael Valley

No bullfrogs were killed by Rotenone




We seined and put out traps and no bullfrogs were
found dead
Frogs can also breathe using their mouths and lungs
However, if tadpoles were present they were certainly
killed
The salamanders were harmed
 It was expensive, smelly and inefficient
compared to other methods
Mechanical or Physical Control
Shooting
Seining
Hand Capture/Gigging
Trapping
Seining
Hand Capture and Gigging

Frogs are pretty hard to catch during the day
unless you have “frog eyes” and can sneak up
on them


Hand capture at night with a flashlight is easier
The best way is to seine
the frogs out of the tank
or stream and either gig
or smash them against
a rock
Trapping
 You
can also use minnow traps to try and
lure in frogs with some bait…
Integrated Pest Management
 A combination
of chemical and physical
controls is the best solution
 New
technologies and solutions need to
be pursued
 More
research about bullfrogs and their
effects need to be done
In Conclusion…

Bullfrogs are a typical invasive species

They should not be made into this terrible
monster

There needs to be a better way to control the
population

Get a hunting license and go eat some
frogs…you’ll help out wildlife all over AZ!
Sources







Clarkson, R.W., DeVos Jr, J.C. The bullfrog, Rana catesbeiana Shaw, in the
Lower Colorado River, Arizona-California. Journal of Herpetology (20)1: 4249. 1986
Hayes, M.P., Jennings, M.R. Decine of ranid frog species in Western North
America: are bullfrogs, Rana catesbeiana, responsible? Journal of
Herpetology (20)4: 490-509. 1986
Hecnar, S.J., M’Closkey, R.T. Changes in the composition of a ranid frog
community following bullfrog extinction. American Midland Naturalist
(137)1: 145-150. 1997.
Moyle, P.B. Effects of introduced bullfrogs, Rana catesbeiana, on the native
frogs of the San Joaquin Valley, California. Copeia (1973)1: 18-22. 1973.
Roach, John. “Invading Bullfrogs Appear Nearly Unstoppable.” National
Geographic News. 28 September 2004.
<http://news.nationalgeographic.com/new/2004/09/0928_040928_bullfrog.ht
ml> 20 November 2006.
Ryan, M.J. The reproductive behavior of the bullfrog (Rana catesbeiana).
Copeia 1: 108-114. 1980.
Spawn, J. Personal field notes pp.24-26. 18 July 2006.