River Ecology and Restoration - River Dynamics and Integrated River Management - page 664

are highly influenced by hunting mortality, which can mask environmental effects. Species with low
populations or restrictions on sampling methods, such as threatened and endangered species, are also
poor indicators because they are difficult to sample adequately.
(4) Response uniformity in different geographic locations. Response of an indicator species to an
environmental stress cannot be expected to be consistent across varying geographic locations or habitats.
If possible, the response to a stress should be more uniform than that of other species in different
geographic locations.
In summary, a good indicator species should be in the middle on the food chain to respond quickly and
have relatively high stability, should have a narrow tolerance to stresses, and should be a native species
(Erman, 1991). The selection of indicator species should be done through corroborative research.
10.3.1.2 Aquatic Macro-Invertebrates
Aquatic macro-invertebrates have been used as indicators of stream and riparian health for many years.
Perhaps more than other taxa, they are closely tied to both aquatic and riparian habitat. Their life cycles
usually include periods in and out of the water, with ties to riparian vegetation for feeding, pupation,
emergence, mating, and egg laying (Erman, 1991). It is often important to look at the entire assemblage
of aquatic invertebrates as an indicator group. Impacts of stresses to a stream often decrease biodiversity
but might increase the abundance of some species (Wallace and Gurtz, 1986). Using benthic macro-
invertebrates is advantageous for the following reasons: (1) they are good indicators of localized conditions;
(2) they integrate the effects of short-term environmental variables; (3) degraded conditions are easily
detected; (4) sampling is relatively easy; (5) they are in the middle of the food chain and provide food for
many fish of commercial or recreational importance; and (6) macro-invertebrates are generally abundant
(Plafkin et al ., 1989).
Field sampling of macro-invertebrates usually requires a combination of quantitative and qualitative
collection methods. The sampling may be performed for one site in a 100 m stretch with representative
areas of flow velocity, water depth, substrata composition, and hydrophyte growth. For a segment of an
investigated stream, collections were made in areas with different current velocity, water depth, and
different substrate sizes. At least three replicate samples were collected at each sampling site at
appropriate depths of 0.15 m of the substrate with a kick-net (1 m u 1 m area, 420 ȝm mesh) if the water
depth is less than 0.7 m. A D-frame dip net may be used to sample along stone surfaces and in plant
clusters. If the water depth is greater than 0.7 m, samples may be collected with a Peterson grab sampler
with an open area of 1/16 m 2 . Replicate samples for each site are combined to form a composite sample,
amounting to at least a minimum area of 1m 2 (Duan et al. , 2007). The cobbles sampled are generally
scrubbed by hand to remove invertebrates and then discarded. The debris and invertebrates are rinsed
vigorously through a fine sieve with a 300 ȝm mesh. Then the macro-invertebrates are taken from the
debris and are placed in plastic sample containers and preserved in 10% formaldehyde in the field.
Environmental parameters, including substrate composition, water depth, water temperature, average
current velocity, and dissolved oxygen concentration, are usually measured and recorded in situ . Growth
and cover proportion of aquatic hydrophytes are also described. All macro-invertebrates are picked out of
the samples and then identified and counted under a stereoscopic microscope in the laboratory. Macro-
invertebrates are identified most to family or genus level except early-instar insects (Liu et al ., 1979),
and each species is assigned to a FFG based on the literature (Plafkin et al ., 1989; Barbour et al ., 1999).
10.3.1.3 Fish
Fish are also used as indicator species. Some management agencies use fish species as indicators to track
changes in habitat condition or to assess the influence of habitat alteration on selected species. Habitat
suitability indices and other habitat models are often used for this purpose, though the metric chosen to