ANIMAL SAMPLING
GENERAL ECOLOGY LABORATORY

Location: Gilmore Creek - various sites

Objective: Use a capture/recapture procedure (p. 124-126) to estimate the brown trout population in a stream section.

Hypothesis: Stream sections of Gilmore Creek support brown trout populations numerically of the same size.

Agenda:

Week 1

1) Collect fish in two (one on Tuesday, one on Thursday), 200-m sections of stream with a backpack electrofisher and dipnets.

2) Count and identify all fish collected.

3) Measure the total length of each fish.

4) Mark each fish by clipping off the upper tip of the caudal (tail) fin and return the fish to the stream.

Week 2

1) Repeat 1, 2, and 3 above.

2) Examine all fish for presence of clipped fins and record such individuals as recaptures.

3) Take multiple measurements of the width of the stream sections sampled.

Analysis:

1) The instructor will construct a total length-frequency plot of the fish collected in each stream section to determine the number of size (age) groups present.

2) Calculate trout population estimates (with standard error and 95% confidence interval) for the total population and each age group within each stream section (use equations 4, 6, and 8, pp. 125-126).

3) Use the appropriate t-test (equation 9, p. 126) to compare total population estimates between sites.

4) Calculate trout population densities for each site using the population estimates and the stream site dimensions.

Equipment:

Backpack electrofisher

Meter tape

Dipnets

Measuring boards

Waders

Scissors