CreditsSlides and notes used in this presentation were provided
for educational purposes by:Virginia Save Our StreamsVirginia
Department of Conservation and RecreationAlice Furguson Foundation
Bridging the WatershedAudubon Naturalist SocietyAnd a very special
thanks to Darrell Schwalm of the Shenandoah Valley TU chapter for
putting this presentation together.
The suitability of a stream for brook trout depends, in part, on
the availability of food. This is a presentation about fish food
how to identify different types of fish food and how fish food can
indicate whether a stream is healthy enough for trout to live.
Lets start our discussion by thinking about how we (people) use
water in our streams and rivers. [Brainstorm with students about
how we use water and organize their responses into three general
categories drinking water uses, recreational uses, and aquatic life
uses.]
Our states and the Federal government have laws that protect our
streams, rives, and lakes for these uses.
State water quality standards are based on three general types
of uses:Drinking waterRecreation uses including swimmingAquatic
life (see text on slide)
Which standard is the most stringent?The suitability of a
stream, river, or lake for drinking water and recreational use
depends primarily on its bacteria and chemical quality.
However, the suitability of a stream for aquatic life is based
primarily on the availability of fish food. This slide tells why
aquatic insects are good indicators of water quality.The more
scientific term for fish food is benthic macroinvertebrate or
macros.Benthic = dwelling on the stream bottomMacro = large enough
to see with the naked eye although a low power field microscope is
helpful to distinguish details.Invertebrate = without a backbone.
Most benthic macroinvertebrates are aquatic insects that have three
body parts (head, thorax, abdominal segment) and six legsOther =
other invertebrate animals that live on the stream bottom include
worms, clams, mussels, and crayfish. Macros are an important link
in the food web between the producers (leaves, algae, etc.) and the
higher consumers such as fish.
[Have the students use their copy of the VASOS ID sheet as you
go through the different organisms quickly.]
There are three key features of macroinvertebrates that help
identify the different animals and species.
The first feature are legs are legs present, how many, and what
type? Be careful because some organisms have structures that may
look like legs such as the lateral filaments used for breathing in
the insect in the slide.The second key feature are tails is there a
tail, and if so, how many parts does it have and what is the shape
of the parts?The third key feature are gills are gills present, and
if so, where are they located on the insect and what are their
shape? Note that there are organisms like some snails that have
internal gills that you can not see.There are some other secondary
factors that also help distinguish one species of
macroinvertebrates from another. The practice specimen to identify
shows some of these other factors: Body shape; Head shape and size;
Wingpads; Placementg of legs; and Antennae
The practice specimen is a dragon fly nymphCrayfish -Note
lobster-like in appearance, 5 pairs of legs, 1st pair modified into
large pinchers, head & thorax combined (cephalothorax), and can
be quite smallMayfly nymph: note three tails (some species have two
tails), abdominal gills visible, and antennaeStonefly nymph: note
long antenna, two tails, no abdominal gills, distinctive separation
of the wing pads on the thoraxLeech: note the segmentation and
absence of head or tailCaddisflies - Order Trichoptera elongate,
generally caterpillar-like in appearance (closely related to
butterflies & moths)3 distinct body parts visible -distinct
head w/ small, simple eyes & usu. inconspicuous antennae3 pairs
of true, jointed legshave cases made of gravel, sand, or organic
matter covering their abdomen (case-making forms often collected
w/o case)complete metamorphosis (no wing pads)Clams, Mussels, &
Snails (Phylum Mollusca)hardened shell covering soft body (for
fresh water species in our area)Clams & Mussels - Class
Pelecypodatwo opposing hinged shellsconcentric growth rings on
shellsvaried colorscan be mistaken for pebblesDragon &
Damselflies - Order Odonatametamorphosis is incompleteeither robust
or elongate body forms w/ distinct segmentshead distinct w/
relatively large, well developed eyeswing pads present in later
instarsprehensile labium (lower lip)3 pairs of true, jointed
legsvaried sensitivity
Damselflies (Zygoptera) - more delicate, thin, cylindrical body
form than dragonfly- three paddle-like gills (caudal lamellae)
protrude from rectum- relatively long, thin legs note three tails
that are featherlike and broader than a mayfly tail, long legs,
long-slender abdomen, protruding eyes on side of headArthropods
(Phylum Arthropoda)jointed legs (adults, not always in
immature)distinct body segmentsexoskeleton (must shed to
grow)Crustaceans - Class Crustaceasegmented bodies2 pair of
antennae
Scud - Order Amphipodalaterally (side-to-side)
flattenedGenerally curled, shrimp-like in appearanceoften swim with
a sideways motion, good swimmersfemales sometimes w/ eggsmore than
6 legsCaddisflies - Order Trichoptera elongate, generally
caterpillar-like in appearance (closely related to butterflies
& moths)3 distinct body parts visible -distinct head w/ small,
simple eyes & usu. inconspicuous antennae3 pairs of true,
jointed legsusu. one or more thoracic plates (but abdomen not
sclerotized)anal prolegs with a single hook on each (closely
appressed to body in case-making forms)some have filamentous
abdominal gills
Net-spinning caddisflies. Note the six legs, three dorsal
plates, and filamentous gills on the underside.Flies - Order
Dipteragenerally maggot-like in appearance, often w/o immediately
distinguishable body partsmay or may not have distinct/visible
headhead, if visible, has simple eyes and inconspicuous or no
antennaeno true, jointed legs and no wing padsmay have prolegs on
thorax or abdomen-abdomen may end in proleg(s) or other terminal
processmetamorphosis is completesome swim w/ jerking motion, others
attach to substrate (or collecting pan), and others crawl on
bottom
Crane fly, a True Fly larva. Usually quite large, with tail-like
projections.Dragon & Damselflies - Order Odonatametamorphosis
is incompleteeither robust or elongate body forms w/ distinct
segmentshead distinct w/ relatively large, well developed eyeswing
pads present in later instarsprehensile labium (lower lip)3 pairs
of true, jointed legsvaried sensitivity
Dragonflies (Anisoptera) - robust bodies from cylindrical to
dorsoventrally flattened- abdomen broadens from base- especially
large eyes- gills in rectal chamber (no external gills); 3 anal
structures- can move by "jet propulsion"
Dragonfly larva: note the tiny three tails and variable body
shapes.Beetles - Coleopteravery diverse, challenging
groupmetamorphosis is complete- some adults are aquatic
(elytra)
For Larvae- body generally elongate, often sclerotized
(hardened)- head usu. sclerotized & well defined, some w/ well
developed mandibles- usu. have 3 pairs of true, jointed legsno wing
padsabdomen may have lateral or terminal filaments
Shown in slide -- Left is an adult water boatman. Top is a water
penny larva, and bottom is a riffle beetle larva. Clams, Mussels,
& Snails (Phylum Mollusca)hardened shell covering soft body
(for fresh water species in our area)Clams & Mussels - Class
Pelecypodatwo opposing hinged shellsconcentric growth rings on
shellsvaried colorscan be mistaken for pebblesSnails - Class
Gastropodasingle coiled or spiral shellextend fleshy "foot" for
locomotion
Lunged snails, with opening on the left. Flat coiled snails are
also lunged snails.Flies - Order Dipteragenerally maggot-like in
appearance, often w/o immediately distinguishable body partsmay or
may not have distinct/visible headhead, if visible, has simple eyes
and inconspicuous or no antennaeno true, jointed legs and no wing
padsmay have prolegs on thorax or abdomen-abdomen may end in
proleg(s) or other terminal processmetamorphosis is complete
True Fly Larva:Top Black fly larva. Very small, with bulge at
one end where it has a suction cup, with which it attaches itself
to rocks, and then waves the projections at the other end to catch
food.Bottom Midge larva a tiny head, two pair of prolegs near the
head and at the tail endHellgrammites, Fishflies, & Alderflies
- Order Megalopteraelongate, somewhat dorsoventrally flattened
forms that can be quite large (3-4") - distinct heads w/ well
developed jaws- 3 pairs of true, jointed legs and no wing pads -
abdomen has lateral filamnts (don't mistake for legs) - abdominal
gill tufts present in some forms (hellgrammite)- abdomen ends
either in either 2 prolegs, each w/ 1 pair of hooks, or in a
single, often brushy filament (latter in alderfly)- may have 2
breathing tubes near end of abdomen (fishfly)- metamorphoses is
complete
Fish fly larva. Note the lateral filaments, or fake legs.
Sometimes very large (up to 4 inches) with sharp biting
jaws.Stream-bottom macroinvertebrates differ in their sensitivity
to water pollution. Some stream-bottom macroinvertebrates cannot
survive in polluted water. Others can survive or even thrive in
polluted water. In a healthy stream, the stream-bottom community
will include a variety of pollution-sensitive macroinvertebrates.
In an unhealthy stream, there may be only a few types of
nonsensitve macroinvertebrates present. Macros that are sensitive
to pollution will be found in healthy streams that are little
impacted by human activities. These streams will normally have a
tree-lined riparian buffer that provides shade to keep the water
cool in the summer, leaves that provide food for aquatic insects,
and tree roots that hold the soil along the stream banks and
prevent erosion.
The stream water will normally be cool in the summer to hold
high levels of oxygen. The stream bed or substrate will include
many riffle areas with cobble size stones that provide abundant
living spaces for a variety of insects. The stream bottom will also
be relatively free of sediments that could fill the spaces between
stones and smother the insects.
Finding pollution sensitive aquatic insects is a good indication
that the stream is very suitable for trout.Somewhat sensitive
macros are found in streams that are moderately impacted by human
activities. These streams have riparian buffers that are only
partially forested so there are sections where stream banks are
eroding and moderate amounts of sediments are entering the stream.
The water temperatures are warmer in the summer because there is
less shade, and dissolved oxygen levels are lower than good quality
streams.The streams have fewer riffle areas, and the riffles are
normally composed of gravel size stones, sands and other fine
sediments that fill some of the living spaces.
The upper reaches of these streams that are least impacted by
human activity, and lower reaches that receive cold spring water
may support a trout population if the water temperatures are cool
enough in the summer to maintain sufficient dissolved oxygen.
Macros tolerant to pollution live in poor quality streams that are
highly impacted by human activity. The riparian buffers are
normally without trees and stream-bank erosion is common. The
stream bottom has a lot of sediment that limits living spaces for
the aquatic insects. Water temperatures are warm in the summer and
dissolved oxygen levels are low at times.
Finding a high percentages of pollution tolerant macros is an
indication that the stream will not support a trout population.All
streams are impacted by human activity. Therefore, it is the degree
of impact that is important to determine whether a stream is
suitable for trout. Little impacted streams are good and highly
impacted streams are bad. These good and bad streams can often be
identify just by looking at them and visually assessing that
environmental factors that indicate a good quality stream forested
riparian buffers, little stream-bank erosion, cobble riffles, and
little sediment on the stream bottom.
Most streams and sections of streams fall in the middle they
have good quality sections and poor quality sections. These streams
are harder to judge. Studies conducted by environmental scientists
have been used to create measurements or metrics that will indicate
the relative health of a stream. There are many metrics that are
helpful, and the best measurements use a variety of metric, or
multimetrics, together to assess the quality of a stream.
Applying metrics to assess the quality of a stream is based on
the assumption that the samples collected to calculate the metrics
follow the same accepted standard procedures used by the scientist
that did the studies.To apply metrics that indicate stream health,
the macros first need to be identified to the order level, and in
some cases, to the family level. The tally sheet is used to record
and organize the results.
There should be at least 200 individual macros identified in the
sample to have a sample that is representative of actual conditions
in the stream. A sample with a small number of macros can provide
misleading results.The diversity of organisms in the sample and the
percentage of each organism in the sample are two important
measures used to assess stream health. Having a high diversity
indicates that the stream has good quality riffles, fast and slow
moving waters, and sections with shallow and deeper water levels.
Healthy streams will have several macro species that are sensitive
and moderately sensitive to pollution. Each macro species has been
given a tolerance level based on scientific studies. Calculating
the tolerance metric indicates the relative abundance of pollution
sensitive species.
The macros that are most sensitive to pollution have the lowest
tolerance number zero is best. The tolerance scale goes up to 10 so
10 is bad. Therefore, the low tolerance metric scores indicate best
quality streams.Combining the scores of the different metrics
provides the best indication of the health of a stream. The
multimetric index is designed so the higher the score, the better
quality the stream.The multimetric index can be used to
characterize the quality of a stream. The VASOS rating system
presented in this slide is not used specifically to assess the
suitability of streams for trout. Rather, it is used to assess
whether a stream is likely to meet the VA state water quality
standards for aquatic life. Many streams that meet this aquatic
life standard will not support a trout population. Therefore, the
streams most likely to support trout are those with the higher
scores, and the streams most unlikely to support trout have the
lower scores.
