I will not be able to set up a drift fence surrounding my vernal pools, but I would like to conduct time-constrained, dip-net searches for adult and larval amphibians (mainly wood frogs and mole salamanders). Is there a set method on performing these time-constrained searches? For example, 20 minutes of searching for every x number of meters. Also, does anyone know of a specific paper that discusses these time-constrained searches in detail?
Hi Chris there are methods for visual encounter surveys. However I would caution you using these for adult Ambystomatidae and for larval frog and salamanders. Adult frogs also differ quite a bit in their behavior, by species and also be time of year and ambient conditions, and this influences their detectability. Wood frogs in particular can be quite cryptic when they are not engaged in breeding behavior and even then, can disappear quickly. Ambystomatids when breeding are not particularly visible unless you are wading in the pool, and even then I always considered myself lucky to spot any in the water column.
For these reasons and others vernal pool researchers began to rely on egg mass counts, anuran call surveys, larval surveys using dipnets and minnow traps (but be sure to stratify), and as you mention, mark recapture with drift fences. Visual encounter surveys can be a good added means of detection.
Since time and money are an issue for you I would go for egg mass surveys, anuran call surveys, dipnet surveys for larvae, minnow traps if you can, and you can add VES as an extra. Remember to do repeated visits so you can calculate detection probability. Egg masses can provide an index of relative abundance if you count carefully and identify to species properly. There is a fairly large literature too big to cite here on amphibian detection and field sampling for presence and relative abundance. Have fun out there.
Thank you Robert. That was very helpful advice. I re-worded the question as well. I was actually not looking to perform "visual" surveys, but dip net surveys. Any specific methods for these would be very helpful. I think the minnow traps are also a great idea, and I would like to incorporate these as well.
Did you check this book?
Amphibian Ecology and Conservation
A Handbook of Techniques
Edited by C. Kenneth Dodd, Jr.
Techniques in Ecology & Conservation
584 pages | 30 line and 30 halftone illustrations | 234x156mm
978-0-19-954119-5 | Paperback | 17 September 2009
I think what you should do is to collect the data in such a way that you can estimate detection probabilities (see the chapters by Bailey & Nichols and Schmidt & Pellet in the book edited by Ken Dodd).
The dip net is the greatest tool ever invented! Every scoop is like a birthday present. Sometimes the presents suck and sometimes they're great. Sometimes the presents take a long time to unwrap. And the presents and their wrapping differs from pond to pond, from day to day, and even from place to place in a pond. (Come on, we all know we dip more often where we know our animals can be found!)
the Dodd edited volume is the best place for a reference. But really, one has to take the references, and then one has to just figure it out and deal with idiosyncrasies in a way that is repeatable from day to day and person to person.
After taking Benedikt's advice I've read the chapters in Dodd edited vol (plus more) and I feel pretty good now about my methods. And Chris, your answer basically rocks. This is how I feel every time I set a turtle trap, check a drift fence, or go looking for an animal. Thank you for the input.
The important thing is to ID and count each animal caught for each dipnet sweep separately. And space the dips far enough apart (e.g. 10 m) to help with independent samples. You should be able to do occupancy modelling if you treat each sweep result as the separate sample I.e., a data file for sweep 1, one for sweep 2, etc. Vernal pools is a variable. That is the way I was told to do it by a modeler.
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