WLF 448: Fish & Wildlife Population Ecology
Lab Notes 3, Fall 2003

Problem Set #4 (Lab 4):

Sightability Model for Elk

Because of your recent experience in analyzing aerial-survey data, you have been asked to analyze another elk data set from the Lochsa River drainage in Idaho. The data were collected from the same study area as in the lab exercise. Sampling strategy and techniques did not change. However, the data were collected 2 years later (1994), and sampling effort was increased to 8 sample units in stratum #1, 7 sample units in stratum #2, and 3 sample units in stratum #3 (low-elk abundance). Total available sample units in the study area are still 8, 9, and 15, respectively (Hint: you enter the total available sample units for number of subunits or population units). The data have been compiled in a file named ELK2.DAT, which is located in the directory k:\wlf\448\aerial6.

Use program Aerial Survey to analyze ELK2.DAT. Name your output file ELK2.OUT. Answer the following questions:

 

Remember all estimates should be reported with a confidence interval

  1. What was the estimated total number of cows, calves, and bulls wintering in the Lochsa study area in 1994? What does the 90% confidence interval really mean?
  2. List and describe the three types of error associated with these estimates.
  3. What is the estimated total number of cows in stratum #1? What percentage of the variance of the estimate of total cows in stratum #1 is due to sightability?
  4. What is the estimated bull:cow ratio (bulls/100 cows) for the study area? 
  5. Why is the variance for sampling error in stratum #1 zero?

Compare 1994’s survey results (elk2.out) to 1992’s survey results (elk1.out). Assume the management objective for this study area is 2,500 elk, with a post-hunt calf:cow ratio of 60 calves to 100 cows. Use the test surveys option (in the analyze menu) to answer the following questions about differences among the 1992 survey, 1994 survey, and management objectives for the study area. Support your answers with statistics from the test surveys output.

  1. Was there a difference between population estimates (total elk) in 1992 and 1994?
  2. Was there a difference between calf elk population estimates (total calf elk) in 1992 and

    3. 1994?

  3. Was the total number of elk wintering in the Lochsa study area in 1992 and 1994 below the management objective for this area?
  4. Was the calf:cow ratio in the Lochsa study area in 1994 below the management objective for this area?
  5. Provide an example where sampling theory and the concept of sightability models could be applied to estimating abundance of fishes? If you were developing a sightability model for your fisheries example, what variables would you investigate as having possible influence on sighting probability (ie., what variables would you include in the regression analysis)?
Turn in the following (due next week):
  1. Answers to questions,
  2. Hard copy of the first page of your output files (e.g., ELK1.OUT, ELK2.OUT) *you will only get credit if your name appears in the title*, and
  3. Output from any Test Surveys analysis that you performed.

Please write your name and the name of the file on your printouts. View your output before printing, i.e., make sure your output is error free before printing.

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Revised: 09 September 2005