 
Predation Exclusion Study
To determine the effect of predators in the bay, I will be comparing
caged plots with control plots in the bay. Half my cages will be fully
caged and (because caging may have a large effect on the system),
half the cages will be ¾ caged. These cages will be assembled
in the bay and data collected per my monthly rotation schedule. Total
time of this experiment will be 4 months.
Because of the cost of building cages, I must find the lowest possible
number of cages that will allow me to see a statistical difference.
Below is a sample of the ‘N’ size of statistics that can
be gathered using a given number of cages.
| Cage # |
3/4 |
Full |
Control |
Transition from 3/4 to full |
Transiton from full to 3/4 |
cost with plastic |
cost with chkn wire |
| 2 |
4 |
4 |
4 |
3 |
3 |
120 |
150 |
| 4 |
8 |
8 |
8 |
6 |
6 |
240 |
300 |
| 6 |
12 |
12 |
12 |
9 |
9 |
360 |
450 |
| 8 |
16 |
16 |
16 |
12 |
12 |
480 |
600 |
| 10 |
20 |
20 |
20 |
15 |
15 |
600 |
750 |
| 20 |
40 |
40 |
40 |
30 |
30 |
1200 |
1500 |
To determine the variability in the bay, I took 100 sq. ft. sized
plots (25 feet by 4 foot transects) in the section of the bay that
I will have the cages. I found the following goby densities (44, 42,
43, 34). The variability is fairly low, which allows me to do
The standard deviation with my small sample size of N=4 is 4.6. Because
of this low variability I have decided to use 6 cages, which gives
me an N of 12 for each variable
|