Our Stream Studies


Crayfish Capture-Recapture

 Identifying and Counting

Sorting Collected Organisms 

Biological Tests and Methods

The riffle survey is completed by each camp group. Invertebrates are collected by the students, using Surber samplers (2). No effort is made to control the number of Surber samples collected by the group. Following collection the organisms are transferred into jars and then placed, for temporary storage, in a refrigerator. This survey also includes the removal and collection of organisms attached to large rocks and boulders at the study site. The organisms collected are counted and identified during the evening laboratory. A classification key, specific for Sinking Creek, and the availability of low power binocular microscopes speeds the process (3) (4). Resulting data from each group are entered in a master data table for analysis.

The crayfish population census is conducted in a defined 3 meter by 30 meter shallow shoreline area of the stream. Crayfish are captured in small hand held dip nets by the student team members. Following capture the crayfish are counted and marked on their dorsal surface with finger nail polish. After counting and marking they are released into the same area. The next day the crayfish are captured again and counted. Marked crayfish are recaptured animals. Using the Peterson Index the total estimated population is, Total Population / Total Marked and Released on Day 1 = Total Captured Day 2 / Captured and Marked Day 2. Students are encouraged to capture more than 50 crayfish from the area on the first day.

Snails are counted by teams of two students. A 1 foot square metal frame is randomly placed along the shoreline of the stream. All of the snails within the frame are carefully collected and counted. This procedure is repeated five times by each team conducting the measurement.

The stream seine survey is the most fun for the students, especially on a warm day. The seine activity requires large numbers of students and often two groups are combined to achieve adequate help. Down stream, (setter) seines are placed across the stream. The seines are attached to three poles which are held by students. Up stream, 50 meters of so, drivers (Students) hold seines across the stream. On command the drivers slowly move down stream, keeping their nets in position, and move fish and other vertebrates into the nets of the setters. When the two groups come together the students "haul" the nets and capture their prey. Following capture the animals are classified, released and the data are recorded (5). On a warm day this procedure might be repeated several times. On a cold day once is enough.

Diatoms, one of the major stream producers, are removed from the water by filtration and then counted using a microscope. Only free floating diatoms are obtained by this method. Pairs of students, working as a team, filter 100 ml and 200 ml samples of stream water. Special Millipore filters and apparatus are used. The exact counting procedure is described in the Millipore manual available from Millipore, 80 Ashby Rd., Bedford, MA 01730.

Total and fecal coliform counts are made once each session. The Hach coli-MUG procedure, when followed carefully, yields excellent and easily observable results (6). The test is done by a single team of two students who prepare the diluted river water and inoculate the coli-MUG tubes. Following inoculation, the tubes are incubated at 35 degrees Centigrade for three days. Total coliform activity (gas production) is seen by the end of the first and second day. Fecal coliform confirmation (tube fluorescence) is seen after three days. The student team completes its work by reading the tubes daily and posting the data on the master table. Discussion of the MPN table with each of the groups is necessary. See the Hach publication, "Coliform Procedures, Multiple Tube Fermentation Technique" for additional information.

Biochemical oxygen demand measurements require 5 days for completion. The test is started by a first session team and the results are read by a second session team. One the first day two dissolved oxygen bottles, one clear and the other painted black are filled with stream water and sealed with the glass stopper. The dissolved oxygen present in the water of the clear bottle is measured and recorded. The black bottle is wrapped in aluminum foil and stored for 5 days. The temperature of the air where the bottle is stored should be approximately 20 degrees Centigrade. After 5 days the dissolved oxygen remaining in the black bottle is measured. The BOD value is the difference between the original measurement and the final measurement.

Current Biological Test Data
1972-Present Biological Test Data
Water Chemistry Tests and Methods

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