11B
Larger
Organisms
EVPP/BIOL
350
Freshwater
Ecosystems
Dr. Lecture Kim de Mutsert
Fishes of Tidal Freshwater
Freshwater
Bluegill
Largemouth bass
Yellow perch
catfish
Fishes of Tidal Freshwater
Estuarine and/or
Anadromous
Striped bass
White perch
American Shad
Killifish
Bay anchovy
Hogchoker
Silverside
A
m
e
r
i
Rozas and Odum (1987) did a study of invertebrates and
c
fish in the tidal Chickahominy near Richmond
a
n They found a mixture of freshwater and brackish water
species
e
Note the high abundance of forage species, food for
e
larger fish
l
Fishes of Tidal Freshwater
(
7
0
)
B
Fishes of Tidal Freshwater
Rozas and Odum (1987)
Note the seasonal
changes in the dominant
species
Banded killfish appeared
early and then dropped
off
Spotted sunfish gradually
increased, perhaps as
SAV cover developed,
then left late in the
season
Grass shrimp were only
found in the later half of
the season, perhaps as
the water became slightly
Fishes of Tidal Freshwater
Rozas and Odum (1987)
Note also the effect of
vegetation on these small
forage species
They obviously cluster in
the vegetated areas
where they are somewhat
protected from predation
Native to western Atlantic
coast from St. Lawrence River
to Florida
Anadromous species: spends
most of its life at sea in large
schools
During average life span of 5
years at sea may migrate over
20,000 km
Enters freshwater in the spring
to spawn
Uses tidal freshwater directly
and consumes prey that are
produced in tidal freshwater
marshes
Provides a link between tidal
freshwater marshes, estuarine
waters and the ocean
American
Shad
American Shad
Spawning occurs in both tidal and nontidal
waters from late March to early June
Spawning may occur many miles above
the head of tide
A single female can produce as many as
600,000 eggs
The eggs and sperm are broadcast into
the water as mixed schools of males and
females congregate
American Shad
There is no nest and no care of the off spring
Eggs sink slowly to the bottom where the embryo
develops and hatching from the egg takes place in
5-6 days
The young larva continues to feed on its yolk sac,
but gradually starts feeding on small plankton
When they reach a couple of inches in length they
can effectively swim and start to join together in
schools and are called young-of-the-year juveniles
American Shad
Young-of-the-year remain in fresh to brackish
water feeding on zooplankton and insect
larvae until early fall when they return to the
sea
As juveniles and adults in the sea, shad feed
on plankton and small fishes
American Shad
As late as 1881 there were 40 permanent
seine fisheries in the North Branch of the
Susquehannah each normally taking
10,000 shad per day
Until the early 1900s the American shad
fishery was the largest in Chesapeake Bay
with annual catches exceeding 22,000
metric tons (25,000 tons)
American Shad
Blockage of spawning rivers by dams and other
impediments and water pollution have severely depleted
American shad spawning habitat
Small dams were constructed in the 1800s for mill
ponds and canal works that blocked smaller tributaries
However, the big blow came in the first part of the 20th
century when the large dams blocked the major streams
The entire Susquehannah basin (largest in the
Chesapeake watershed) was blocked by the Conowingo
dam and three others just upstream.
The Chesapeake Bay fishery yielded only 700 metric
tons annually in the early 1990s.
American Shad
Efforts are now in place to restore
American shad populations
These involve:
Removing barriers such as dams
Putting in fish ladders or otherwise facilitating
fish passage
Improving quality
Restoring water stocks from hatcheries
American Shad
At Conowingo, American shad congregate
downstream of the dam
They are captured and transported upstream by
truck to spawning areas: trap and transport
Shad larvae and fingerlings are produced in a
hatchery and released into the spawning areas
The larvae and fingerlings will grow and
gradually be transported downstream just like a
fish that had hatched in the stream
They can pass over the dams, although some
may be damaged in the process
American Shad
The Conowingo restoration effort seems to
be paying off
Catches of upstream migrating shad
below the dam have increased from about
100/yr in 1972 to 27,000 in recent years.
The hatchery fish are marked (antibiotic in
otolith (ear bone)) and most of the
returning fish are from the hatchery
American Shad
Access to spawning sites on the Potomac
River has also been impeded, although
not entirely blocked by dams
Stocking of fish began in 1994 with nearly
16 million shad larvae (fry) stocked into
the river
In January 2000 a fishway was completed
at Little Falls dam
American Shad
The population has gradually rebounded over
the stocking period and now is sufficient to
support a natural recovery
American Shad
One Potomac tributary, Pohick Creek, was
blocked by poor water quality
Chlorinated effluent from a Fairfax County
treatment plant had eliminated whatever
anadromous fish runs had survived
In the mid 1980s the treatment regime was
changed and the chlorine removed before
discharge
Some spawners have returned, but not yet
American shad
Wetland Animal Communities
Wetland Animal Communities
Some are resident
in tidal fresh like the
freshwater species
Some are
anadromous and
semianadromous
and use tidal
freshwater for
spawning
Some are
catadromous and
spawn in the ocean,
but live as adults in
freshwater
Non-resident
species are called
transient
Birds of Tidal Freshwater Wetlands
Great Blue Heron
Mason Neck: One
of largest rockeries
in East Coast!
Other herons
Egrets
Green Heron
Great Blue Heron eating a
small fish, their main prey
Birds of Tidal Freshwater Wetlands
Bald Eagle
Osprey
Both prey on fish
Birds of Tidal Freshwater Wetlands
Ducks and Geese
Dabbling ducks,
Canada geese and whistling
swans prefer tidal freshwater
to salt marshes
They eat plants as well as
invertebrates
Wood duck is the only duck species
that nests regularly in freshwater
tidal marshes
Birds of Tidal Freshwater Wetlands
Wading Birds
Rails and Shorebirds
Gulls and terns
These birds tend to eat
invertebrates in the shallow
near shore area
Rail
Killdeer
Sandpiper
Birds of Tidal Freshwater Wetlands
Sparrows, finches
Blackbirds, wrens
These birds eat insects and
seeds in the high marsh areas
Redwing blackbird
Marsh wren
Marsh sparrow
Other vertebrates
Amphibia
- Amphibians are most closely related to fishes
- Less than 100 species in North America divided into
frogs, toads, salamanders and newts
- Eggs are laid in water, most juveniles live a
fish-like existence and then leave the water as adults
Axolotl
Other vertebrates
Reptilia
- Worldwide, 23 species of
crocodilians
- A few hundred species of aquatic
snakes
- 300 species of turtles
- A few lizards than can be
considered aquatic
- All lay leathery-shelled eggs in
moist vegetation near water
Other vertebrates
Mammalia
- None truly aquatic, spend significant portion on land
- Mostly rodents: beavers, muskrats, nutria, capybara
- Some semi-aquatic mammals are protected (river otter in
Europe)
- some are a nuisance
Nutria
(introduced nutria in Louisiana)
Capybar
a family
Biotic indices
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