Lake Guntersville Largemouth Bass

Maceina et al. (1995) examined the population of harvestable Largemouth Bass (Micropterus salmoides) in Connor Cove of Lake Guntersville, Alabama in March, 1992. Their objective was to estimate the abundance of harvestable bass through the depletion of catches due to electrofishing. In their study, they electrofished for 15 minutes at each of four depth strata. The total number of bass captured and removed from the population in the full hour of electrofishing at the four depths was recorded. Thus, a total of one hour of electrofishing constituted one unit of effort. Six one-hour periods were used to deplete the population of bass in one area of Connor Cove. The number of bass caught in each successive sampling period was 23, 12, 13, 14, 9, and 7. Use these data to answer the following questions.

  1. Enter the catch and effort data into separate R vectors. Calculate a vector from these vectors that represents the 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 catchability coefficient? Very carefully interpret what this estimate means relative to Connor Cove Largemouth Bass. How does your estimate compare to the estimate published in Maceina et al. (1995)?
  3. What is the best estimate and 95% confidence interval for the initial population size? How does your estimate compare to the estimate published in Maceina et al. (1995)?
  4. Estimate the expected number of bass that would be caught in the first sampling period given your best estimates of q and N0, and the amount of effort used in each sample period.
  5. Estimate the expected number of bass that would be caught in the second sampling period, again given your best estimates of q and N0, and the amount of effort used in each sample period.

 

Benthic Fish in a Headwater Stream

Pritchard et al. (2021) used three methods to determine the abundance of benthic European Bullhead (Cottus gobio) in a stony headwater stream in Northern Yorkshire, England. In one part of their study they set block nets at the up- and down-stream ends of a site called “Footbridge.” The researchers then used a backpack electrofishing unit deployed from the lower to the upper limit of the site to capture and remove all Bullheads from the site (the removed fish were placed downstream below the lower block net). After a short break, this process was repeated two more times. A total of 138, 55, and 48 Bullheads were removed on the successive electrofishing passes. Use this information to answer the questions below.

  1. What is the best estimate and 95% confidence interval for the probability of capture during each electrofishing pass.
  2. What is the best estimate and 95% confidence interval for the population size? How does your estimate compare to the estimate published in Pritchard et al. (2021)?
  3. Pritchard et al. (2021) estimated a “capture efficiency.” Use your results to show and then describe what they mean by this.
  4. Is there evidence that the probability of capture differed after the first pass?