assessing grazing intensity

Ivor Williams i.d.williams at
Mon May 31 18:20:43 EDT 1999

I would very much appreciate some practical advice on field methods for 
assessing grazing intensity by herbivorous fishes.  I am currently doing field 
work in Belize looking at fish abundance and benthic communities and would like 
to assess fish bite rates within 5*5m plots on 12m deep forereef areas.

I had planned to approximately follow the AGRA protocol (5 min abservations of 
1 sq meter areas), but find either (most of the time) there are no fish grazing 
during the 5 minute period, or there are about 20 small fish frantically 
nibbling and it is impossible to keep track. The resulting data set is 
something like 0, 0, 387, 0, 6, 513... so, not only is there are a large 
element of guesstimation in the replicates with large numbers of bites, but 
also the replication necessary to get meaningful data looks horrendous. My 
feeling now is that I might be better to follow individual fishes for fixed 
periods and then try to use average grazing rates to convert fish abundance 
data into grazing intensity, but I would prefer to directly assessing grazing 
itself.if it is feasible.

Thanks for any help you can give

Ivor Williams

Centre for Tropical Coastal Management
Department of Marine Sciences
Ridley Building
University of Newcastle upon Tyne
Tel: +44 (0)191 222 5868
Fax: +44 (0)191 222 7891
Belize phone 00 501 26 3856

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