Enumeration of Fish or Other Aquatic Animals
251
EXERCISES
OPTION 1
OPTION 2
Select a small pond, reservoir, or stream with a readily observable population of fish or
salamanders. On several consecutive sampling days (at least four or five), collect as many
individuals as possible, count and mark them, and then return them to the lake or stream. If
this were a class project, various groups would be responsible for sampling on different days,
but be certain that identical procedures are followed.
1. A variety of methods have been used to mark fish and other animals so that individuals
would be recognizable at a later date. The most common method of marking fish or
salamanders in short-term studies is by mutilation of a fin or other appendage. Clipping
part of a fin or foot provides an easily recognizable mark, but regeneration usually obliterates
the mark within a few months. Alternatively, small holes (or other shapes) can be punched
into the opercula or fins of some fish and are identified easily during short-term studies.
Branding, tags, tattooing, radioisotopes, and other markings all have been used to identify
organisms in mark-and-recapture studies. See Everhart et al. (1975) for additional information on marking fish.
2. For each sampling date or trial, record the following information:
a. Total number of individuals captured.
b. Number of marked individuals captured.
c. Number of marked individuals returned to habitat.
d. Time spend in collection.
e. Type of equipment used.
f. Location of sample area.
g. General observations.
3. Estimate the population of individuals by:
a. The Petersen method.
b. The Schnabel method.
c. The Schumacher-Eschmeyer method.
4. Calculate the confidence interval for estimates made by both the Petersen and the Schnabel
methods.
This option can be done as a demonstration or laboratory exercise.
Procedure: Work in pairs!
1. Set up a data sheet with headings according to the Schnabel method.
2. Place a few handfuls of dried beans (the "fish") in a can (the "lake").
3. With the eyes closed to facilitate taking a random sample, remove several seeds with your
hand.
4. Count the seeds; mark each with a waterproof marking pen; record the numbers in the
proper places on the data sheet (Table 18.1); and return the seeds to the can and mix
thoroughly by stirring or shaking vigorously.
5. With eyes closed again, take another random sample; count; record the marked and
unmarked ones; mark the unmarked ones and return them all to the can; mix; and calculate
the total number of seeds in the can.
6. Repeat step 5 until estimates begin to approximate one another.
7. When estimates become more or less constant, verify the last estimate obtained (presumably
251
EXERCISES
OPTION 1
OPTION 2
Select a small pond, reservoir, or stream with a readily observable population of fish or
salamanders. On several consecutive sampling days (at least four or five), collect as many
individuals as possible, count and mark them, and then return them to the lake or stream. If
this were a class project, various groups would be responsible for sampling on different days,
but be certain that identical procedures are followed.
1. A variety of methods have been used to mark fish and other animals so that individuals
would be recognizable at a later date. The most common method of marking fish or
salamanders in short-term studies is by mutilation of a fin or other appendage. Clipping
part of a fin or foot provides an easily recognizable mark, but regeneration usually obliterates
the mark within a few months. Alternatively, small holes (or other shapes) can be punched
into the opercula or fins of some fish and are identified easily during short-term studies.
Branding, tags, tattooing, radioisotopes, and other markings all have been used to identify
organisms in mark-and-recapture studies. See Everhart et al. (1975) for additional information on marking fish.
2. For each sampling date or trial, record the following information:
a. Total number of individuals captured.
b. Number of marked individuals captured.
c. Number of marked individuals returned to habitat.
d. Time spend in collection.
e. Type of equipment used.
f. Location of sample area.
g. General observations.
3. Estimate the population of individuals by:
a. The Petersen method.
b. The Schnabel method.
c. The Schumacher-Eschmeyer method.
4. Calculate the confidence interval for estimates made by both the Petersen and the Schnabel
methods.
This option can be done as a demonstration or laboratory exercise.
Procedure: Work in pairs!
1. Set up a data sheet with headings according to the Schnabel method.
2. Place a few handfuls of dried beans (the "fish") in a can (the "lake").
3. With the eyes closed to facilitate taking a random sample, remove several seeds with your
hand.
4. Count the seeds; mark each with a waterproof marking pen; record the numbers in the
proper places on the data sheet (Table 18.1); and return the seeds to the can and mix
thoroughly by stirring or shaking vigorously.
5. With eyes closed again, take another random sample; count; record the marked and
unmarked ones; mark the unmarked ones and return them all to the can; mix; and calculate
the total number of seeds in the can.
6. Repeat step 5 until estimates begin to approximate one another.
7. When estimates become more or less constant, verify the last estimate obtained (presumably