CFP Field Survey & Data Collection 3 — Questions and Answers
Question 1: A biologist uses a stratified random sampling design for a lake survey. The primary advantage over simple random sampling is:
- It requires fewer total sampling stations
- It reduces variance within strata and improves precision for subgroups (Correct answer)
- It eliminates observer bias entirely
- It does not require prior knowledge of the lake's structure
Correct answer: It reduces variance within strata and improves precision for subgroups
Stratified sampling reduces overall variance by grouping similar units together, improving estimates for each stratum.
Question 2: When sampling benthic macroinvertebrates in a riffle habitat, the Surber sampler is preferred because it:
- Samples a defined area while a net captures dislodged organisms downstream (Correct answer)
- Filters the entire water column simultaneously
- Operates effectively in pool habitats with soft substrate
- Requires no disturbance of the substrate
Correct answer: Samples a defined area while a net captures dislodged organisms downstream
The Surber sampler frames a fixed area and catches organisms dislodged from that substrate with a downstream net.
Question 3: Catch-per-unit-effort (CPUE) data are most useful when:
- Gear efficiency remains constant across surveys (Correct answer)
- Species composition changes dramatically between samples
- Water clarity varies widely among sites
- The gear type is changed between sampling periods
Correct answer: Gear efficiency remains constant across surveys
CPUE is a valid index of abundance only when catchability (gear efficiency) is consistent across time and space.
Question 4: A trawl survey is being conducted in a large reservoir. At minimum, how should tow locations be selected to ensure representative sampling?
- Only at known fish aggregation points
- Randomly or systematically across available habitat types (Correct answer)
- Exclusively in the deepest areas
- Along the shoreline only
Correct answer: Randomly or systematically across available habitat types
Random or systematic placement across habitats ensures unbiased coverage and representative CPUE estimates.
Question 5: Which of the following is a major limitation of using scales for aging fish compared to otoliths?
- Scales cannot be collected without killing the fish
- Scale annuli may be reabsorbed or false rings may form, reducing accuracy (Correct answer)
- Scales are only present in juvenile fish
- Scales do not exhibit annual growth patterns
Correct answer: Scale annuli may be reabsorbed or false rings may form, reducing accuracy
Scale resorption during periods of stress and false check formation can cause underestimation of age.
Question 6: During electrofishing, a biologist notices reduced catch rates despite no change in effort. Which factor is most likely responsible if water temperature has increased significantly?
- Increased fish swimming speed allowing escape from the anode (Correct answer)
- Decreased electrical conductivity requiring higher power settings
- Reduced species diversity in warm water
- Net fouling reducing effective sweep area
Correct answer: Increased fish swimming speed allowing escape from the anode
Warmer water increases fish metabolism and swim speed, allowing fish to escape the electrical field more easily.
Question 7: A biologist records substrate composition in a stream using the Wentworth scale. A particle measuring 32 mm would be classified as:
- Sand
- Gravel
- Cobble (Correct answer)
- Boulder
Correct answer: Cobble
The Wentworth scale classifies particles 16–256 mm as cobble, so a 32 mm particle falls in the cobble category.
CFP Field Survey & Data Collection 3
A biologist uses a stratified random sampling design for a lake survey.
The primary advantage over simple random sampling is: