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What's
In a Name?
Paddlefish a.k.a.
Spoonbill: from its snout that looks similar to that of a paddle
Polyodon: (Polly´-oh-don)
means "many toothed" in Greek
spathula:
(spat´-you-lah) from "spatula", referring to the shape of its snout
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Where
Do They Live?
Paddlefish currently inhabit the lower St. Croix River and the Mississippi
River below the Ford Dam. They used to be much more abundant in these
rivers than they are now, and they used to occur in the Minnesota River
up to Mankato. Paddlefish prefer large rivers and riverine lakes (places
where rivers spread out and become more like lakes--Lake Pepin and Lake
St. Croix are examples) that are deep and wide. They often are found with
sturgeons, catfishes,
carpsuckers, buffaloes, and common carp.
"Cool Fact":
The paddlefish is a species of ancient origins. It shares several characteristics
with sharks such as a spiral valve in its intestine, gills inside of spiracles
on its head, and a lot of cartilage in its skeleton.
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How
Big Do They Get?
How
Long Do They Live?
Paddlefish may be among the fastest growing fish in North America rivers.
Records show them reaching 732 mm (almost 29 in) in one year. In Minnesota,
they eventually grow to be 1.2-1.3 m (48-52 in) long and reach 13.6-22.6
kg (30-50 lbs). Many years ago one weighing more than 91 kg (200 lbs)
was reported from Lake Okobji in Iowa. Paddlefish are hard to age accurately
beyond 9 or 10 years. So, we often do not get age information for large
fish. We know they live for at least 20 years and suspect they live much
longer than that.
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What
Do They Eat?
The size of paddlefish suggests that they might be great piscivores (fish-eaters).
In reality they are planktivores (eaters of microscopic plants and animals
floating in the water). They are the biggest planktiore in Minnesota. A
paddlefish uses special sensors in its long, paddle-like snout to detect
tiny electrical currents created by groups of plankton (the microscopic
plants and animals). It opens its huge mouth and swims forward straining
the water through its gill rakers. In this way, it consumes huge amounts
of plankton each day and grows to its enormous size. |
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What
Eats Them?
We do not know much about young paddlefish and so we are not sure what
eats them. Because of their great size, adult paddlefish have few predators.
Their greatest predator today is the chestnut lamprey. Lampreys do not
consume entire paddlefish, (read about the chestnut
lamprey) but they can weaken one and in extreme cases may case death.
As many as 30 lampreys have been found attached to a single paddlefish.
In the late 1800s and early 1900s, humans were by far the greatest predators
of this fish. Today, paddlefish are protected from commercial and sport
takes in Minnesota.
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How
Do They Reproduce?
Female paddlefish do not mature until they are 9-10 years old and do not
spawn every year. Males mature at about 7 years old. Spawning starts in
the early spring when water temperatures reach about 10° C (50° F) and
water levels are on the rise from snowmelt and spring rains. Like sturgeon,
paddlefish migrate from lakes and rivers into streams in search of gravel
bars in water 3 m (10 ft) or less deep. As far as we know, they make no
nests. Instead they swim over the gravel in groups and release their eggs
and sperm. Once they are done spawning, the parent fish go back to the
lake or river from which they migrated. A single female can lay a huge
number of eggsÐ300,000 to 600,000, depending on her size and age. We know
nothing about the early life history of this species in the wild, other
than we occasionally find larvae drifting in streams in late April and
early May.
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Conservation
and Management
Like lake sturgeon, paddlefish were very abundant in Minnesota during the late 1800s and early 1900s. They have declined to their low numbers today because of over-fishing and changes to their habitat. At the turn of the previous century, commercial fishers could take over 454 kg (1,000 lbs) of paddlefish from Lake Pepin in a single collection! We think that paddlefish populations continue to decline today because dams and other barriers interfere with their migration, and polluted streams interfere with embryonic and larval development. Also their long life cycle makes it hard for populations to recover quickly.
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Permission is granted for the non-commercial educational
or scientific use of the text and images on this Web document. Please credit
the author or authors listed below.
Photographs by Konrad P. Schmidt
Text by Nicole Paulson & Jay T. Hatch in
cooperation with
the Minnesota Department of Natural Resources' MinnAqua Aquatic Program
This page developed with funds from the
MinnAqua Program
(Minnesota Department of Natural Resources, Division of Fisheries)
and the
Sport Fish Restoration
Program (Fish and Wildlife Service, US Department of the Interior)
Maintained by Jay T. Hatch
General College and James
Ford Bell Museum of Natural History
University of Minnesota, Minneapolis/St.
Paul