It would be better to go for mechanical grabs for the sample collection on selection of the collection sites. Moreover, it depends on the understanding of the biology of the perticular clam which are under investigation for example salt tolerance/resistance, levels of organic load, etc.

I'm not sure exactly what's possible, but we've had luck using SCUBA with person-hours as a measure of density.

We also use scuba and free divind, depending on the river type. Just, I am thinking what is the confidence of the analyses? I mean, with scuba you can assess limited area. On the main course, you can not dive, since the traffic is too intense. We were thinking to make some kind of combination - diving, hand net sampling and benthological dredga. What do you think is it effective enough to express each sample as the relative abundance (1,3,5,7,9,) and latter too combine the vaues, but to incorporate pondering (depending on the participation of each (micro)habitat?

Underwater camera maybe also useful to estimate abundance and diversity of shallow underwater communities. There are a few camera brands with affordable price that can do the job

I would offer up this publication. There are many ways to sample large rivers. It all depends on the questions you are asking. Strayer, D.L., and D.R. Smith. 2003. A guide to sampling freshwater mussel populations. American Fisheries Society Monograph 8, Bethesda, Maryland 103 pp.

A searchable bibliography of over 20000 references on freshwater mollusks can be found at: http://ellipse.inhs.uiuc.edu:591/mollusk/biblio.html

THANKS!!!

Momir

Malcolm Elliott's book on the statistical analysis of samples of freshwater invertebrates remains an essential, highly readable and often salutary guide to the realities of calculating population abundance estimates. It can be found here: https://www.fba.org.uk/scientific-publications-sps.

Thanks a lot for detail responses. Momir

I have worked some on quantifying mussels in the St. Lawrence River. This is a very large river with complex substrate, places of great depth as well as shallows, and tremendous current. I have two approaches: 1) use of regularly spaced boat-based grab and dredge samples along linear transects of the river; 2) use of scuba-based hand counting at sites evenly spaced along linear transects from shore out across the river, using a steel cable circle template with an area of exactly 1 square meter. The latter method is much more accurate, as it allows counting of all individual mussels within a standard square meter at uniformly spaced sites, regardless of substrate or water depth. The problem is that this method is labor intensive, costly, and hazardous. Let me know if you want more details.

Thanks David - we perform similar procedure - free diving, scuba diving (hand picking within 0.5x0.5 frames), dredging transects (transects are defined by GPS), in combination with hand net sampling. This give some idea about densities. In addition, we use relative abundance scale (1-5) to combine results of different sampling techniques. Still, I am not sattisfied with results. How you deal with combination of techniques?

Hey you can select a transect of particular measurement (eg., 100 m) along the river and sample all the substrate-type seen in the stretch. Of course each substrate-type require a different combination of technique for sampling benthos. The benefit of selecting stretch is you can cover all type of habitats within the river and this can be consider as a sampling point.