Czypinski and Ogle (2011) performed an experiment to determine if a population of invasive Ruffe (*Gymnocephalus cernuus*) could be significantly reduced by sequential removal of Ruffe with bottom trawls. The following catches of Ruffe were made at the Kakagon River location with the corresponding minutes of trawling effort.

```
Sample 1 2 3 4 5 6 7 8 9 10
--------------------------------------------------------
Catch 282 346 27 4 9 27 4 0 1 0
Effort 19.0 30.0 31.0 20.0 29.5 42.5 34.5 36.0 27.0 25.0
```

- Enter the catch and effort data into separate R vectors and create a vector that represents CPE in each sampling period. Carefully interpret the meaning of the first value in the CPE vector.
- What is the best estimate and 95% confidence interval for the initial population size?
^{1} - What is the best estimate and 95% confidence interval for the catchability coefficient? Very carefully interpret what this estimate means relative to the capture of Ruffe at this site.

^{1} Note that Czypinski and Ogle (2011) used the Ricker modified formula.

- Suppose that 5 minutes of trawling was considered to be one unit of effort. Convert the effort vector accordingly and calculate a new CPE vector. Carefully interpret the meaning of the first value in the CPE vector.
- What is the best estimate and 95% confidence interval for the initial population size? How does this estimate compare to the same estimate from using the original effort data? What does this mean?
- What is the best estimate and 95% confidence interval for the catchability coefficient? How does this compare to the same estimate from using the original effort data? What does this mean?

- What is the best estimate for the percentage of the Ruffe population that was removed in all trawling efforts at this site?

Solution Code:

Available upon request to students not in a class. Contact fishR maintainers.

## References

Czypinski, G. D., and D. H. Ogle. 2011. Evaluating the physical removal of Ruffe (

*Gymnocephalus**cernuus*) with bottom trawling. Journal of Freshwater Ecology 26:441–443.