crayfishpresentation (PDF)

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Author: Tiffany Beachy

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The sex ratio of crayfish will remain constant
from stream to stream as any factor that could
effect the population would effect both
genders equally.

IntroductionCrayfish, often called crawdads and crawfish, are crustaceans and
members of the order decapoda. There are two families of crayfish native
to the the United States: Astacidae and Cambaridae, with Cambaridae
being more prevalent in the Eastern United States and in Great Smoky
Mountain National Park. Crayfish typically live in shallow streams and and
lakes (1-2m deep). Since crayfish have trouble living and cannot reproduce
in a polluted or acidic stream they are commonly used as indictors of
stream health. Therefore analyzing their ability to breed serves an
effective way to study the population of crayfish and water quality. In
order to survey their ability to reproduce we assessed the sex ratio of
crayfish (female: male) and how it varies from stream to stream

We would like to thank Dawn Dextraze
for her guidance and advice, Andrew
O’Neil for his epic crayfish wranglin’,
Tiffany Beachy’s support and help, and
all the Tremont Staff!

Measuring Crayfish

MethodsThe materials that we needed consisted
of nets, bins and a recording journal. At
the two streams we scouted three
different areas. At each area we
measured out 11 meters up/down stream
from our spot of origin. Then we timed
our each for thirty minutes at each of our
three areas at both streams. Our searches
consisted of flipping rocks and searching
the damp cavernous areas underneath
the shore. The recorder records the claw
to tail of each specimen, as well as asses
the gender of the crawfish; and but all of
the data into our data sheet.

Purchase Knob


Future Considerations-



Tremont Sizes


5.6 cm

4.9 cm

Purchase Knob Sizes
4.9 cm

5.6 cm

We rejected our hypothesis because the gender
ratios varied between Purchase Knob and Dorsey creek. However, the sample size was so small, we could not create
a definite ratio to compare. At Purchase the best ratio we could find was 0.71. At Tremont, we found a ratio of 1.82.

DiscussionFrom this data, we can conclude that the ratios depend on each other. For example, in the first transect of the Tremont location
we found many average-sized females and few males. We can guess that this section of the Dorsey Branch stream is where the
females find safe refuge from the large, violent males. Also, we found many juvenile/baby crayfish so this must be where the
females lay and hatch their eggs. In the middle transect we saw an equal amount of males and females which were bth quite
large. This may mean that this section is where breeding occurs because the most sexually mature individuals were in this area.
The uppermost section of the stream had many more males than females and they were mostly average-sized. So we can
hypothesize that this is where the young bachelor crayfish go before they can fight for a mate. In the Purchase Knob stream
Transects, the crayfish collection was not great enough to create a definite conclusion to compare. Therefore we choose to
compare the different transects on the Dorsey Branch Stream in Tremont. Overall, from the data we have collected we can see
the patterns among female and male crayfish.

An ideal future experiment would account for
discrepancies in two major categories:
accuracy and variable variety. First, our
transects were supposed to be eleven meters
long. However, this length was measured in
human paces. The unstable geography of the
stream made this measurement inaccurate.
Also, our sample sizes were extremely small,
making the data nearly invalid anyway. Also,
we measured our crayfish by length from claw
to tail. However, several of the crayfish were
missing claws. In future experiments, it would
be advisable to measure from the carapace
instead of the claws. We also could have
measured factors dependent on the stream
itself, like flow rate, depth, width, leaf cover,
and rock size.
Searching the Stream

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