Very interesting project!
Will it take place in freshwaters?
What techniques will you use for sampling fish larvae / juveniles at the microhabitat scale?
How are you going to describe the vegetated beds?
A Malagasy PhD student is presently trying address identical questions in Toliara Bay, SW Madagascar (so, tropical marine species, a lot of them unknown at larval & juvenile stage...).
Best regards
Dominique
all the best
if you will use a new modern techniques for smapling instead of using plankton nets just share it with us,
Regrads
SAMPLING TIPS: HOW DO I FIND THESE FRESHWATER CRITTERS?
The best methods for collecting freshwater invertebrates will vary with habitat types and your study objectives. If your objective is to assess the condition of a stream, you really need to collect as many invertebrate types ('taxa') as you can, to build up a picture of the range of taxa living in that habitat.
Collecting samples: shallow stony streams
A good sampling method for shallow stony streams involves placing a net (we use a mesh size of 0.5 mm, but a large kitchen sieve with 1-mm mesh works too!) in the stream and disturbing the streambed immediately upstream. Fine material including invertebrates will drift into the net (or sieve).
Collecting samples: weedy and stagnant habitat
In weedy and stagnant habitats, you may need to sweep a net through submerged vegetation to collect sample material. You don’t need to collect bucketloads of material – we usually collect about 400 ml of material. Whatever method you use, make sure you do it safely!
Processing samples
Once you’ve collected your sample, it’s a good idea to place the net contents into a shallow white tray with enough water to allow invertebrates to swim or crawl (they may be hard to see until they start moving). You may need to spread your sample over several trays to see a wide range of invertebrates. You can do this in the field, or take the sample material back to the lab or classroom for a closer look. Of course magnifying glasses or microscopes will allow you to see the invertebrates in a great deal more detail.
Yes, the project is in a freshwater estuary on the Western end of Lake Superior (St. Louis River).
We use a benthic sled that we hand pull across a transect in shallow waters. It is a 1 x 1 m frame that sits on wide "skis" with a 500um mesh. It also has a roll bar mounted on the bottom from to keep it from uprooting vegetation. It is not a common gear type, but it works well in our system because we have soft substrates and few logs/debris.
The samples are processed on the boat by spraying down the net into the cod end. We then rinse any large debris/plant material and discard it. After sieving out the water the samples are preserved. Sometimes this a daunting, messy process in the field.
The fish are later sorted out from other sample material under a microscope or light table depending on how messy the samples are.
We characterized vegetation in two ways. The first was a random stratified quadrat survey of plant taxa and visual estimates of percent cover for each dominant species. The second is a hydroacoustic survey using the Biosonics system that gives us nice overall percent cover, depth, biovolume and plant height measures.
Dominique, the tow sled looks a bit like the net shown here...
http://content.cdlib.org/view?docId=kt1k4001gs&chunk.id=d0e939&&doc.view=entire_text
Hi
In order to answer this question/problem, several remarks have to be studied.
1. General remarks:
Research studies are usually carried out on sample of subjects rather than whole populations. The most challenging aspect of fieldwork is drawing a random sample from the target population to which the results of the study would be generalized. The key to a good sample is that it has to be typical of the population from which it is drawn. When the information from a sample is not typical of that in the population in a systematic way, we say that error has occurred. In actual practice, the task is so difficult that several types of errors, i.e. sampling error, non-sampling error, Response error, Processing error,…
In addition, the most important error is the Sampling error, which is statistically defined as the error caused by observing a sample instead of the whole population. The underlying principle that must be followed if we are to have any hope of making inferences from a sample to a population is that the sample be representative of that population.
2. A key way of achieving this is through the use of “randomization”. There several types of random samples, Some of which are: Simple Random Sampling, Stratified Random Sampling, Double-stage Random Sampling... Moreover, the most important sample is the simple random sample which is a sample selected in such a way that every possible sample of the same size is equally likely to be chosen. In order to reduce the sampling error, the simple random sample technique and a large sample size have to be developed.
3. Specific remarks:
The following factors are highly affected the sample size and need to be identified:
- Population Size,
- Margin of Error,
- Confidence Level (level of significance) and
- Standard of Deviation.
4. Then, the sample size can be estimated by,
Necessary Sample Size = (z-score or t-value)2 * StdDev*(1-StdDev) / (margin of error)2 .
Regards,
Zuhair
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