RIO GRANDE SURVEY PROTOCOL
Protocol for Big Bend National Park Amphibian Monitoring Field Crew
During nocturnal surveys by canoe along the Rio Grande, we quantify adult amphibians using area-constrained searches. We also record some habitat and river characteristics.
RIVER SECTIONS
From West to East along the Rio Grande (Fig. 1):
1) Santa Elena take-out to road pull-off just east of the Desert Mtn. Overlook (mi 0.9)
2) Solis to Rooney’s Place
3) Gravel Pit to RGV group campground
4) RGV group campground to end of road at Boquillas Canyon entrance
Figure 1.
Survey both the Texas and Mexico sides of the river. Amphibians are seen by shining miner's headlamps on the bank while a few may be heard chorusing. Record what is seen and heard and record UTM coordinates. Only collect any bullfrogs seen or heard on the Texas side of the river and record UTM locations for them. Do not step onto the Mexican bank for any reason.
EQUIPMENT NEEDED
MINIMUM WATER LEVELS FOR EACH SECTION
1) Santa Elena take-out to road pull-off just east of the Desert Mtn. Overlook (mi 0.9)
River gauge: Castolon ³ 3.1 ft.
2) Solis to Rooney’s Place River gauge: Johnson Ranch ³
3.5 ft.
3) Gravel Pit to RGV group campground River gauge: RGV ³ 1.75
ft.
4) RGV group campground to Boquillas River gauge: RGV ³ 1.75
ft.
Note: These are not set required river levels. These are to be used as a guide for when the water is high enough canoes won't drag on the bottom and you won't have to walk much of the way. Be wary of water that is too high and therefore dangerous. If in doubt, talk to the river rangers.
BEFORE SURVEY
Arrive about 1 hour before dark (30 minutes before sunset) to set up canoes, drop off the shuttle car at the take-out point, flag the take-out, and take initial measurements. Measurements to record at the start of the survey include air temperature, water temperature, average wind speed, and dissolved oxygen. On the data sheet record these measurements along with river stretch, date, observers, put-in time, sky code, nearest river gauge level, previous 2-3 days' weather, and moon phase. Each canoe should survey one side of the river. Be sure to write on each data sheet what side is being surveyed, Texas or Mexico. Also, take a water sample, approximately 0.5 m from the shore and avoiding silty water, to conduct water quality tests in the lab.
RIVER SURVEY METHODS
Put in the river at least 30 minutes after sunset. It should be dark enough that you need lights to see. Avoid doing river surveys on full moons or when the moon is very bright and up at the time of survey. Make sure all gear is placed securely in the boat and that EVERYTHING is tied down. Tie in the clip board with data sheet so it can not be "thrown" overboard.
The person in the bow shines the miner headlamp along the bank and records amphibians seen. The person in the stern paddles and steers the canoe and also looks for amphibians when possible. The person in the stern also reads off UTM coordinates when needed. The speed of the canoe should be slow but steady. Float along with the speed of the water. Speed and visible bank habitat will change with river level.
Count amphibians seen and record species. Record whether they are adults or juveniles. If there are many amphibians in a small area (about 20 m) simply clump the count with the UTM coordinates and time seen. Record the substrate the amphibian is on: rock, mud, water. Record the dominant vegetation around them: Arundo (A), Phragmites (P), Tamarisk (T), Baccharis (B). Note if an individual is collected. Also record any other animals seen (e.g. snakes, nutria, beavers, ringtail cats) and their UTM locations.
For amphibians heard chorusing, record the chorus code (CC: 0=none heard, 1=no overlapping calls, 2=some overlapping calls, 3=full chorus) and estimate the number of individuals calling and species. Record as follows: Species cc(# of individuals). Example: Rber 2(4).
AFTER SURVEY
Link Water Analysis Protocol
Record time end. Measure air and water temperature, wind speed, and sky code at the take-out. Load gear in/on car, don’t forget the other car, and go home. Recharge miner headlamps, AA batteries, and GPS battery. Return river permit to Panther Junction visitor center.
Anaylze water sample within 48 hours.
Results
This table shows the mean # of individuals and Variation (CV =
coeffiecient of variation = SD/
) in
Counts of Rio Grande Leopard frogs and bullfrogs along the four survey stretches of the
Rio Grande. If any bullfrogs are caught during the survey, put them in a labelled
tube in the refrigerator after the survey. Then, follow the methods below.
| Rio Grande Leopard Frog | Bullfrog | |||
| Mean | CV | Mean | CV | |
| Gravel Pit-Rio Grande Village | 158 | 0.49 | 0.67 | 1.73 |
| Solis Landing- Rooney's Place | 75 | 0.77 | 2 | 0.5 |
| Rio Grande Village- Boquillas | 118 | 0.46 | - | - |
| Santa Elena-Castolon | 61.33 | 0.07 | 4.33 | 0.26 |
Figure 2 & 3. These figures show the # of individuals of various species counted during repeated surveys of the Gravel Pit - Rio Grande Village and Rio Grande Village - Boquilla stretches.
BULLFROGS
Bullfrogs are not native to Big Bend but have recently moved into the area and may be impacting native amphibian populations. To kill the bullfrogs, remove them from the refrigerator for at least 1 hour. To humanely kill a bullfrog, rub a small amount of Anabesol on its head. In approximately 3 minutes the frog should be dead. Put the dead bullfrog in a labeled plastic bag - species, location, date, time, UTM coordinates - and store in a freezer. At the end of the season, bullfrogs as a group are shipped on dry ice to a lab for contaminant analyses. Also place 2 pieces of 100% bond paper with the same information written on it in pencil into the bag as a backup identifier.
RECOMMENDATIONS
Standardize observer 1 and 2. Or just have one person counting amphibians so that the search effort is standardized.
Only use one type of search light so that the type of light used is standardized and counts do not vary with differing light sources.
PRIMENet Amphibian Monitoring Program
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