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NFC: darters
Pennsylvania's Dynamic Darters
by Andrew L. Shiels
Darters are among the most vividly colored, behaviorally complex,
ecologically important and abundant fishes found in Pennsylvania. Yet,
how many visitors to the Commonwealth's waterways have ever seen a darter
in the wild or even realize that such creatures exist? As the smallest
members of the perch family, they rarely exceed four inches in length.
For this reason, no one looks at them as table fare, as we see the yellow
perch and walleye. Although they are sometimes used as bait by anglers,
they are not as popular as blacknose dace, shiners or stonecats. Still,
darters are arguably the most attractive of all Pennsylvania fishes in
terms of physical appearance. This is especially true of the males during
the breeding season.
Darters are also an important biological component of the waterways they
inhabit. Each species has evolved to occupy a specific niche, which
allows partitioning of available habitat and food resources among other
fishes. Darters prey on insects and crustaceans, and in turn are preyed
on by species such as smallmouth bass and walleyes. Thus, darters are one
link in the larger chain of their aquatic environment. The presence of
darters in a waterway reflects good water quality and diversity of
appropriate habitat.
Attractive or not, we are learning more about the various darter species
and their interactions in Pennsylvania's waterways. The roles that
darters play and the functions they perform continue to emphasize their
importance.
Description
The taxonomic classification of darters is a continuing process. New
species and/or subspecies continue to be described by ichthyologists
using advanced techniques to discern differences and similarities among
isolated or nearby populations. Darters are perch-like fishes grouped
into the Percidae family and are restricted in distribution to North
America. Three genera of darters comprise over 150 North American
species. They represent greater than 20 percent of the 750 species of
freshwater fish found in the United States and Canada. Currently, two
genera of darters are recognized as occurring in Pennsylvania. Twenty-one
darter species are split between the genus Etheostoma (13 species) and
the genus Percina (8 species). Until recently, the genus Ammocrypta was
represented in Pennsylvania by a single species, the state endangered
Eastern Sand Darter. However, this species, formerly known as Ammocrypta
pellucida, was recently renamed by taxonomists and is now named
Etheostoma pellucida--that is, at least until another researcher can make
a more compelling case for it to return to the genus Ammocrypta.
Why they're "darters"
A darter's ability to maneuver in, around and under rocks and substrate
gives it an advantage as a bottom forager. Riffles and swift currents
provide protection for darters because few predators can live there. Many
darters such as the johnny darter do not possess a swim bladder. This
lack of buoyancy allows them to stay near the bottom and facilitates
their rapid darting movements. In addition, bottom-dwelling darters
possess flattened, downward-sloping heads. This feature lets them take
advantage of water flowing to help plane or push down on the fish's head,
thereby helping the fish to remain near the bottom. Conversely, mid-water
darter species such as the blackside darter do possess a swim bladder to
help them remain suspended in the water column.
Overall, darters are small. However, there is considerable variation in
maximum length among the species found in Pennsylvania. The Eastern sand
darter (2.0 inches) and the Tippecanoe darter (1.8 inches) are the
smallest Pennsylvania darters. The logperch and greenside darter can each
reach lengths of 6.5 inches and are the largest darters in the
Commonwealth.
In nature, it is usually true that "form follows function." So it is not
surprising that the Eastern sand darter has a different body shape than
its stream-dwelling cousins. This species lives primarily in lakes or
slow-moving waters and burrows into the sand for protection. The sand
darter is proportionally much longer and thinner than its flowing water
relatives. This lets it quickly wriggle into the sand, leaving only its
eyes exposed. This tactic provides the sand darter with protective cover
in areas where rock or gravel substrate does not exist.
Feeding
Darters are mid-depth and bottom-dwelling fishes. Their location and
movements depend on substrate type as well as the velocity, chemical and
thermal composition of their liquid environment. They seek their prey
among the rocks, gravel or sand along the stream or lake bottom. Prey
items typically range in size up to approximately 3/16-inches.
Prey selection varies with the lifestage of the fish. Juvenile darters
consume small crustaceans such as cladocerans, copepods and ostracods.
Adults prefer chironomids (midge larvae), simulids (blackfly larvae),
ephemeropterans (mayflies) and trichopterans (caddisflies). Large darter
species such as the longhead darter may also eat amphipods (freshwater
shrimp), isopods (sowbugs) and crayfish.
Darters rarely compete with most minnow species because the minnows often
occupy the upper levels of the water column. Food availability and water
velocity help to determine the activity levels of darters' foraging. For
example, in pools or areas of slower current, darters range farther to
procure food. Similarly, when flow rates are high, travel is reduced.
Feeding is primarily by sight, so darters are daytime feeders. Still,
peaks in feeding activity typically occur early and late in the day.
Reproduction
Reproduction in darters generally takes place during the spring and
summer. Day length, or photoperiod, is important in initiating
reproductive activity among darters. Water temperature plays a larger
role in termination of spawning activity. For many darter species
spawning has been reported to occur over extended periods of several
months. Also, there is evidence that females of some species may spawn
several times during the reproductive season. Sexual maturity for many
species can occur at age one. However, egg production increases with age.
Mature female darters can produce between 230 and 1,000 or more eggs,
depending on the species.
Spawning by darters is accomplished in one of three ways, depending on
the species. All members of the genus Percina and some Etheostoma bury
their eggs in the substrate. The eggs are abandoned and there is no
parental care.
Using a different approach, some Etheostoma species, such as the
greenside darter, attach their eggs to submerged vegetation or rocks and
then abandon them. In this case the female releases one to three eggs at
a time and attaches them to a rock, stick or plant.
The most complex and energetically demanding strategy is used by species
such as the johnny darter and fantail darter. These darters engage in
nest building and cluster spawning. The male digs out a nest underneath a
flat rock in preparation of mating with one or several females. After
mating, the female attaches the adhesive eggs to the underside of the
rock. The male then provides care and protection for the eggs until they
hatch.
Generally, in darters and many other fishes, the colorful appearance and
perhaps courtship dance of the male is sufficient to attract a female for
breeding. However, the male fantail darter attempts to improve his
chances by displaying an additional feature that is especially attractive
to females. Female fantail darters prefer to mate with males that already
have eggs. To the female this is probably a signal that the prospective
male is a good "risk." That is, he has already demonstrated that he has
the physical fitness to protect a clutch of eggs to their maturity. But
what if the male has not previously mated with another female or has been
unable to commandeer a clutch of eggs from another male? Theoretically,
he would not be selected by the female for breeding.
In response, male fantail darters develop fleshy knobs consisting of
modified epidermal cells at the tips of the spines on their first dorsal
fin. These knobs, also known as egg mimics, resemble the shape and color
of actual darter eggs. Researchers have shown that female fantail darters
prefer to breed with males that display egg mimics. Even though these
fleshy knobs may also be useful as tools in housekeeping of the nest,
their primary function is as a female attractant.
Distribution
Darter species are neither randomly nor evenly distributed throughout the
Commonwealth's waterways. Before man-induced changes on the North
American landscape, fishes were distributed by natural forces. Glacial
advances and retreats, emergence of mountain ranges and erosion of
watershed-separating barriers all contributed to present-day fish
distributions.
Today, the greatest concentration of darter species occurs in northern
Alabama and eastern Tennessee. The number of darter species declines in
North America as the geographic distance from that region increases.
Tributaries of the Mississippi River were the main routes of darter
dispersal throughout the eastern United States. However, the Appalachian
Mountains apparently served as enough of a physical barrier to reduce the
dispersal of species eastward. As a result, Pennsylvania waters in the
Ohio River Basin contain a greater diversity of darters than the
Susquehanna River Basin and Delaware River Basin, respectively.
In many cases the headwater areas of Pennsylvania streams in the Ohio
River Basin represent the northern or eastern limits of the range for a
particular species in North America. Some of these darters are listed as
state endangered, threatened or candidate species because of their rarity
within the borders of Pennsylvania. As such they are protected by special
regulations. In addition, projects involving activities that may
adversely affect these species are reviewed by Commission staff in an
effort to conserve the remaining populations.
Often species are present in a watershed because of human activities. At
least one species, the banded darter, appears to have been introduced to
a watershed where it is non-native by way of unintentional stocking or a
bait bucket introduction. Historic fisheries surveys in the Susquehanna
River watershed did not reveal the presence of this species. However, in
the 1960s it was discovered in an upper Susquehanna River watershed
tributary.
This species is currently well-established particularly in the main stem
of the Susquehanna River. Since this species occupies a niche similar to
darters native to the Susquehanna River Basin, adverse interspecific
competition may result. This situation is currently being studied.
Ecological interactions
Besides the role that darters play as both predator and prey, there are
undoubtedly other interactions that remain to be discovered. An important
relationship still under investigation involves darters and freshwater
mussels. Some fish species, including darters, are integral to the
reproductive cycle of native Pennsylvania mussels. After a female
freshwater mussel has mated and developed larvae, they must be dispersed
into the aquatic environment where they eventually settle to the bottom
to mature into adults. These microscopic larvae, which are also known as
glochidia, are released into the water column and attach to the gills of
certain fish species.
Typically, only one or a few fish species are suitable for attachment by
the glochidia of a given mussel. Mussels cannot swim, so the fish
provides a means of transport for distribution of the larvae into other
areas of the stream. Some Pennsylvania streams that contain endangered,
threatened or candidate darters also contain endangered mussels.
Therefore, the continued existence of the mussels is directly linked to
the survival of the host fish. It is probable that specific darter/mussel
relationships will become apparent as the research continues.
Regulations
Anyone wishing to capture or study darters in the Commonwealth's waters
should consult the Summary of Fishing Regulations and Laws or contact the
nearest Fish and Boat Commission Regional Law Enforcement Office. Species
that are not listed as endangered, threatened or candidate can be
captured with the same gear that is legal for gathering baitfish.
However, it is unlawful to catch, take, kill or possess protected
species. Because identification of darters can be difficult, especially
for the amateur, study these fishes in their own environment without
removing them.
Provided that state or local regulations allow it and adequate safety
measures are taken, snorkeling is a great way to observe and gain an
appreciation for these beautiful fish. Their colors and interesting
behaviors can rival that of fishes in more exotic locations, such as the
Caribbean. Various field guides are now available to aid in species
identification, and many university libraries contain more advanced texts
on darter ecology.
Protection and conservation
Darters thrive in clean, unpolluted water. Threats to their survival
include habitat alteration or loss, point and nonpoint source pollution,
and competition in the form of exotic species introductions. Acid mine
drainage, particularly in streams of the Ohio River Basin, has degraded
or eliminated many miles of darter habitat.
Sedimentation is especially harmful to darters. Excessive sediment and
silt can smother eggs or reduce populations of forage items. For example,
mayfly nymphs are a staple in their diet. However, many species of
mayflies are susceptible to the harmful effects of sedimentation. Thus,
if the forage declines, the darters must select another forage or begin
to suffer. As diversity of prey declines, so does the diversity of
predators until eventually the chain begins to break down.
Water quality protection strategies that effectively address habitat
loss, alteration and pollution must keep pace as increased demands are
continually placed on Pennsylvania's aquatic resources. Darters will
remain a dynamic part of Pennsylvania's aquatic heritage as long as the
quality of their habitat is sufficient to support them. Appreciation of
darters and their habitat will increase as more Pennsylvanians discover
these seldom seen but very important fishes.
French Creek, Where Darters Go with the Flow
Although darters occur throughout Pennsylvania, one waterway contains an
exceptional diversity of darters and other aquatic species. Beginning in
southwestern New York, French Creek flows 117 miles to its confluence
with the Allegheny River in Franklin, Pennsylvania. Almost 1,270 square
miles of land in Chatauqua County, New York in addition to Erie,
Crawford, Mercer and Venango Counties in Pennsylvania are drained by
French Creek.
Stream flow reversals resulting from glacial activity changed the
prehistoric course of French Creek to its present-day southerly flow in
the Ohio River basin. Previously, French Creek flowed north into the
Atlantic Ocean via the St. Lawrence River system. Glacial activity caused
aquatic species present in the St. Lawrence River system to be "captured"
and added to those species present in the Ohio River system.
When stream flows changed direction, the darters and other species had no
choice but to "go with the flow." Consequently, French Creek exhibits an
unusually high number of fish and invertebrate species. With 70 species
of fish and 26 freshwater mussel species, French Creek is the single most
diverse waterway in Pennsylvania. Thirteen (61 percent) of the 21 darter
species found in Pennsylvania are known to occur in French Creek.
Bioloically speaking, French Creek may be the most important stream in
the state.
Pennsylvania Darters
Common Name Scientific Name Drainage Basin
Occurrence
Species
* Status
Greenside darter Etheostoma blennioides E, O, S, P, G Common
Rainbow darter Etheostoma caeruleum E, O Common
Bluebreast darter Etheostoma camurum O Threatened
Iowa darter Etheostoma exile E, O Candidate
Fantail darter Etheostoma flabellare E, O, S, P, G Common
Swamp darter Etheostoma fusiforme D Extirpated
Spotted darter Etheostoma maculatum O Endangered
Johnny darter Etheostoma nigrum E, O, G Common
Tesselated darter Etheostoma olmstedi S, D, P Common
Eastern sand darter Etheostoma pellucida E, O Endangered
Tippecanoe darter Etheostoma tippecanoe O Endangered
Variegate darter Etheostoma variatum O Common
Banded darter Etheostoma zonale O, S Common
Logperch Percina caprodes E, O Common
Channel darter Percina copelandi E, O Threatened
Gilt darter Percina evides O Threatened
Longhead darter Percina macrocephala O Endangered
Blackside darter Percina maculata E, O Common
Sharpnose darter Percina oxyrhyncus O Extirpated
River darter Percina shumadri O Common
Shield darter Percina peltata S, D Common
Abbreviations: E = Lake Erie, O = Ohio River, G = Genesee River, P =
Potomac River, S = Susquehanna River, D = Delaware River.
* Species Status: Protected status as of January 1, 1997.
Robert Rice
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