Download WLE 340 – Kenduskeag Stream Smallmouth Bass Project – Lab I

SFR 101 – Diversity and abundance of stream fishes
August 29, 2012
Instructor: Steve Coghlan, UMaine Department of Wildlife Ecology
The objectives of this field exercise are to:
1) describe how energy flows through a stream food web and supports fish
production
2) explain how stream, forest, and ocean ecosystems are interconnected
3) learn the physical and biological principles of electrofishing
4) collect and identify stream fishes with electrofishing
5) compute indices of diversity and abundance for stream fishes
6) assist state and federal fishery biologists in assessing Ducktrap Creek, a spawning
and nursery stream for wild Atlantic salmon
An Introduction to Fish Ecology in Small Forested Streams
In Maine and many other regions in the temperate zone, over 70% of watershed
area is drained by headwater streams (defined as 1st, 2nd, and 3rd order streams; a 1st order
stream is a stream with no tributaries flowing into it; a 2nd order stream is formed by the
confluence of two 1st order tributaries; a 3rd order stream is formed by the confluence of
two 2nd order tributaries; and so on and so forth). Headwater streams in forested regions
are typically narrow, shaded by the forest canopy, and have a high shoreline-to-volume
ratio. Shading and groundwater inflow maintain low and relatively constant temperatures.
Because of the heavy shading, little sunlight reaches the stream bottom, and very little
photosynthesis occurs within the stream. Thus, primary production of algae, mosses, and
vascular plants within the stream system itself (termed “autochthonous production”) is
very low. However, sunlight can reach the trees adjacent the stream (or at least trees in
the canopy), and much photosynthesis occurs in the surrounding forest. Throughout the
year, and especially during autumn, bits of vegetation such as leaves, twigs, bark, fruit,
and even whole trees fall from the forest into the stream. This supply of primary
production originating from outside the stream system (termed “allochthonous
production”) forms most of the base of the food web inside the stream.
Some allochthonous material is nutritious and easy to process (such as sugar
maple and red alder leaves), whereas some is nutrient poor and difficult to process (such
as conifer needles and bark). Microbes such as bacteria, fungi, and protozoans colonize
this material after it falls into the stream and produce a slimy layer rich in protein and fats
(called “biofilm”) on top of the carbohydrate-dominated vegetation bits. Aquatic insects
such as mayflies, caddisflies, and some stoneflies feed upon the microbe-vegetation
complex in a variety of ways. Some insects have large, powerful mouthparts and can bite
off chunks of material directly; these insects live typically in leaf-packs and are called
“shredders”. Other insects (called “collector-gatherers”) scurry around on the stream
bottom picking up smaller bits that the shredders have left behind, and still other insects
(called “collector-filterers”) strain even smaller bits from flowing water. In the few
stream habitats that receive direct sunlight through a canopy gap, insects called “grazers”
scrape algae and moss from the tops of rocks. Predatory insects such as dragonflies,
hellgrammites, and some large stoneflies feed directly upon the shredders, collectorgatherers, collector-filterers, and grazers. As bits of the microbe-plant material are
processed, they and their insect processors flow downstream in swift currents and settle
to the bottom in slow currents. Thus there is a “spiraling” of vegetable and insect matter
up and down in the water column in a generally downstream direction, and typically the
largest particles and the most shredders are found upstream, whereas the smallest
particles and most collector-filterers are found downstream.
Stream fish form the next level in the food web, feeding on virtually all aquatic
insects and other invertebrates, smaller fishes, terrestrial insects falling in from the forest
canopy, and occasionally amphibians and small mammals. Like insects, fish show a
variety of adaptations towards feeding on a variety of foods present in flowing water.
Some species lie in wait near the stream bottom, adjacent to a swift current that serves as
a conveyor belt supplying insects drifting in the water column. When it spots a morsel of
drifting food, the fish tips its head and pectoral fins upwards, the current carries it
towards the surface where it can snatch the food from the drift; a few flicks of its tail
drives it back down to its resting spot on the bottom. This method of “drift-feeding” is a
very energetically-efficient way to make a living in a swift, rocky stream. Fish such as
brook trout, Atlantic salmon, creek chub, and fallfish are predominately drift-feeders.
Other fish inspect the bottom in slower currents picking insects carefully from rocks; this
“benthic-feeding” behavior is displayed by species like white sucker and slimy sculpin.
Fish like common shiner and blacknose dace display very opportunistic behaviors,
switching between benthic and drift feeding depending on food availability, often
roaming in schools at the tail end of pools. Other fish, such as chain pickerel and
redbreast sunfish, are ambush predators, lying in wait in very still water and darting out
to intercept a passing insect or small fish.
Finally, stream fish depend on connectivity among various habitats in the stream
to complete their life cycle. Movement of fish within streams and among rivers is very
common, and is probably much more widespread and extensive than appears at first
glance. Some fish will live most or all of their lives within a very short reach, but this is
probably not the norm (for example, in the case of fish that live upstream of an
impassable waterfall). More frequently, fish will move among different habitats
seasonally, as environmental conditions change, and between spawning, nursery, and
feeding habitats. Atlantic salmon provide one of the best examples of large-scale
movements among very distinct habitats. Spawning occurs in the fall in swift gravel beds
in small- to medium-sized streams. Embryos incubate in the protection of gravel nests
over the winter, and fry emerge during the late spring. As fry grow, they may remain
fairly close to their nest site (with tens of meters), may travel downstream into larger
stream reaches, or may travel upstream into headwater streams (especially if larger
reaches present high temperatures and abundant predators). After 1-4 years of growth in
the stream, Atlantic salmon undergo a process called “smoltification” in which they
become more streamlined and silvery, they lose their juvenile banding and spotting, they
become more restless with the urge to move downstream, and their physiology changes
so that they can tolerate seawater. Eventually they migrate downstream through large
river reaches as smolts and enter the sea, where they feed and grow for several years.
When mature, they return to the same stream in which they were spawned and complete
their life cycle. Clearly, failure to access one of the many habitats necessary to complete
their life cycle (such as headwater streams) will result in population collapse.
Overview of the Research Issue
Historically, the northeastern US was heavily forested, and because the structure
and function of headwaters streams draining these watersheds was tied inextricably to the
surrounding landscape as described above, stream fish such as brook trout and Atlantic
salmon are truly “creatures of the forest”. Current fisheries management and forestry
professionals must understand this if sustainable fisheries and sustainable forestry are to
coexist. The past, present, and future status of Atlantic salmon in Maine rivers depends
upon an the functional connection among streams, forests, and the ocean. In this exercise,
we are focusing on stream fishes in general, and Atlantic salmon in particular, to educate
forestry students in basic fisheries ecology.
Ducktrap Creek flows into West Penobscot Bay south of Belfast, ME.
Historically, the Ducktrap (and many other streams in Maine) provided valuable
spawning and nursery habitat for sea-run Atlantic salmon, but currently produces few, if
any, fish. Causes for the Atlantic salmon decline here and elsewhere include dams,
deforestation, overfishing, pollution, acid rain, exotic species invasion, and poor marine
survival. Any wild Atlantic salmon produced in the Ducktrap were classified by the
federal government as part of the Gulf of Maine Distinct Population Segment (GOM
DPS) in 2000, and therefore receive federal protection under the Endangered Species Act.
Besides the Ducktrap, other watersheds within the original GOM DPS range included the
Sheepscot, lower Penobscot (below the Veazie Dam), Cove Brook, Pleasant,
Narraguagus, Machias, East Machias, and Dennys. In 2009, the GOM DPS was amended
to include the entire Penobscot, Kennebec, and Androscoggin Rivers, excluding those
reaches upstream of impassable falls. Most of these river-specific populations are
sustained by stocking hatchery-raised Atlantic salmon, although some natural
reproduction occurs. Two other DPSs in the US, that once inhabited rivers from the
Connecticut River northeastward to the Saco River, are now extinct. Thus Maine is truly
the last stronghold for wild sea-run Atlantic salmon in the US.
The Maine Department of Marine Resources, Bureau of Sea-Run Fisheries and
Habitat (DMR-BSRFH; formerly the Maine Atlantic Salmon Commission) monitors the
abundance of juvenile Atlantic salmon and other stream fishes in the Ducktrap and
elsewhere with electrofishing surveys. The abundance of juvenile Atlantic salmon
provides biologists with a measure of reproductive success of wild fish or the survival
rate of stocked fish, and often is an indicator of habitat quality and a predictor of future
adult returns. The abundance of other stream fishes provides important information on
ecosystem structure, function, and productivity in general, and more narrowly, on
possible competition and predation facing juvenile Atlantic salmon. Furthermore,
variation in the abundance of juvenile Atlantic salmon and other stream fishes over time
provides biologists with information on short- and long-term changes in stream habitat
quality, which is a function of both natural variability and human influences in the
watershed (such as deforestation, urbanization, exotic species introduction, and climate
change).
Field Methods
We will be estimating the diversity and relative abundance of stream fishes at a
DMR-BSRFH monitoring site on Ducktrap Creek by electrofishing. There are many
potential measures of “diversity” that we could compute, but we will restrict ourselves to
the “Shannon-Wiener” index, which accounts for both the richness (number of unique
species present) and evenness (how the total number of individuals is distributed among
all the species present). The equation for this index is presented below, and requires us to
identify individual fish to species and count them. Ideally, we would design our study so
that we could compute the “absolute abundance” of each fish species, which is possible
but very time-consuming and logistically difficult. Instead, we will compute “relative
abundance” as “catch-per-unit-effort”, or CPUE, which is a common metric in fisheries
ecology. This equation is presented below as well.
Aside from identifying and counting individuals of ALL species, we also will
record lengths and weights from all Atlantic salmon that we collect. We will measure
total length (from the tip of the snout to the tip of the depressed tail) in millimeters and
total weight in grams. Eventually, we will provide our data to DMR-BSRFH biologists
for their records, so it is important to pay close attention to collecting and recording
methods. Furthermore, electrofishing can be dangerous if not executed properly, so we
will discuss safety procedures and desired effects on fish in a streamside lecture before
we begin sampling.
Gear checklist
Each crew should have the following gear:
1)
2)
3)
4)
5)
6)
7)
electrofishing backpack and accessories (anode, cathode, gloves)
3-4 scap nets
Several buckets and tubs
Aerators or livewell
Clipboard w/ data sheets and pencils
Measuring board
Scale and weighing tray
Procedures
1) Read all handouts carefully.
2) Divide into 3 teams of ~6 students each, and be prepared to shift duties so that all
students can take part in all activities (typically, we would not change duties in
3)
4)
5)
6)
7)
the middle of a sampling episode, but because this is for educational purposes, all
students should take part in all activities)
Journey to the downstream section of your study reach (which your instructors
will have marked with flagging before you arrive), and organize an electrofishing
crew of 1 shocker, 3-4 netters, and 1 bucket holder.
Double-check all electrofishing settings under advisement of your instructors, and
be sure to follow all safety procedures. Remember to reset the time counter to
zero before you begin.
Electrofish your study reach thoroughly. Starting at the downstream boundary,
electrofish in a zig-zag pattern across and upstream until you have reached the
upstream boundary. Make sure that you alternate duties so that all crewmembers
who want to wear the backpack unit get to do so.
Hold your captured fish in a livewell, process them (species ID, count, and
lengths / weights of Atlantic salmon), and record data (including time spent
electrofishing).
Release fish carefully back into the stream
Deliverables
By the deadline agreed upon by instructors and students, students should submit the
following results electronically, in spreadsheet form:
1)
2)
3)
4)
A list of species and numbers of fish collected by each team
Shannon-Wiener Index values for each team
CPUE values (all fish, and just Atlantic salmon) for each team
A list of lengths and weights measured on Atlantic salmon
Note that one well-constructed spreadsheet table could contain all the
computations necessary for, and the results from, deliverables 1,2, and 3 above, so
think carefully about how best to organize and present your data!
5) Finally, submit the Shannon-Wiener Index and the CPUE (for all fish combined)
for Ducktrap Creek (and the class) as a whole. Think carefully about how you
should do this – is it better to compute an overall H’ and an overall CPUE by
calculating the mean from the results generated from each of the 6 crews’
samples, or to simply combine data from all 6 crews first and then compute
overall results?
Equation 1: Shannon-Wiener Index of Diversity (H’)
R
H '   ( pi  log pi ) , where
i 1
H’ = the Shannon-Wiener Index of Diversity
R = # of unique species (i.e., species richness)
pi = the proportional abundance of species i
log pi = the logarithm of the proportional abundance of species i
pi 
ni
, where
N
ni = the number of individuals of species i collected
N = the total number of individuals of all species collected
(note: technically, you can use any base for which to compute the logarithm, but conventionally, most
ecologists use either log base 10 or log base “e” , also known as the natural logarithm. Here, all students
should use log base 10 so we can compare results among crews.)
Equation 2: Catch-per-unit-effort, or CPUE
n
, where
t
n = number of individuals collected
t = time spent electrofishing (seconds)
CPUE 
(note: you should compute CPUE both for 1) just Atlantic salmon, and 2) for all fish combined. DMR
biologists will enter these values in their database)
Appendix 1: The following table format might be a good example of how to start
inputting your data prior to computations and submission of deliverables
Species
Atlantic salmon
common shiner
blacknose dace
.
.
.
All species combined
Time spent electrofishing
Team 1
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Team 2
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Team 3
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Team 4
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Team 5
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Team 6
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