assessing grazing intensity

Peter van Treeck van_treeck at
Tue Jun 1 04:42:34 EDT 1999

Dear Ivor,

What about interval video camera? We did that and it worked fine.  The
camera took a sequence of 2 sec every 2 minutes the whole day.  With high
resolution cameras it is possible to identify the grazing species as well
as the number of bites. First results can be found in van Treeck,
Schuhmacher & Paster (1996)Grazing and Bioerosion by Herbivorous Fishes -
Key Processes Structuring Coral reef Communities.  in Reitner, Neuweiler,
Gunkel (eds)Global and Regional Controls on Biogenic Sedimentation.I. Reef
Evolution. Research Reports.- G=F6ttinger Arb. Geol. Palaeont. SB2, 133-137
Goettingen Check as well Bruggemann (1994)Parrotfish grazing on coral
reefs- A trophic novelty. PhD Thesis Groningen, NL

Cheers Peter

Ivor Williams schrieb:
> I would very much appreciate some practical advice on field methods for
> assessing grazing intensity by herbivorous fishes.  I am currently doing =
> work in Belize looking at fish abundance and benthic communities and woul=
d 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 abservatio=
ns of
> 1 sq meter areas), but find either (most of the time) there are no fish g=
> 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, b=
> also the replication necessary to get meaningful data looks horrendous. M=
> feeling now is that I might be better to follow individual fishes for fix=
> periods and then try to use average grazing rates to convert fish abundan=
> data into grazing intensity, but I would prefer to directly assessing gra=
> 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
> NE1 7RU
> Tel: +44 (0)191 222 5868
> Fax: +44 (0)191 222 7891
> Belize phone 00 501 26 3856

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