Abundance from Depletion Data

Chequamegon Bay Ruffe

Estimate abundance of Ruffe in Chequamegon Bay, Lake Superior (WI) from experimental trawling data.
Exercise
Depletion/Removal
Abundance
Ruffe
Invasive Species
Author

Derek H. Ogle

Published

Dec 23, 2022

Modified

Feb 13, 2023

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

 

  1. 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.
  2. What is the best estimate and 95% confidence interval for the initial population size?1
  3. 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.

 

  1. 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.
  2. 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?
  3. 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?

 

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

 

Solution Code:

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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.

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