Green2009-herbivore monitoring

Monitoring Functional Groups of Herbivorous Reef Fishes
Pears 2003). This method is less precise than using a differential GPS, and the GPS should be used
if possible.
The optimal distance covered in each timed swim should be 400m to ensure enough distance is
covered to encounter highly mobile species that tend to be rare, patchy or clumped in distribution
(Choat and Pears 2003). If observers are consistently covering distances less than 400m in each
timed swim (e.g. due to a large number of small and medium sized individuals that one observer has
to count), the methods should be modified until an average distance of 400m per timed swim is
attained. This can be achieved by either: 1) Increasing the duration of each swim from 20mins to 25
or 30mins; 2) Reducing the transect width for small and medium sized individuals from 5m to 3m
(1.5m either side of the observer); or 3) Changing the fish sizes that each observer has to count so that
both observers are counting a similar number of individuals (e.g. by one observer counting small
individuals only, and the other observer counting medium and large sized individuals). In that situation,
transect widths for each size group (small, medium or large) remain the same.
Combination of Belt Transects and Long Swims
Belt transects should be used where a higher degree of precision is required or when monitoring for
multiple objectives, and when time and conditions are suitable for laying tapes at each site. This method
provides the most effective technique for monitoring most small (