Paddlefish - Polyodon spathula
The paddlefish is an ancient, mostly cartilaginous fish with a smooth skin. It is a close relative of sturgeons. Although it is sometimes called a spoonbill or spoonbill cat, it is not closely related to catfish. Most species of paddlefish are now extinct, and fossil paddlefish from 60 million years ago have been found in the Missouri River basin near Fort Peck Reservoir, Montana (AFS website 2003).
Montana is home to one of the few remaining self-sustaining populations of paddlefish, and harbors the largest individual fish as well. Specimens have been taken weighing up to 150 pounds.
Paddlefish are readily identified by the long paddle-like snout, long, tapered gill covers, and the "backbone" bent up into the upper lobe of the tail fin. The body is smooth and virtually scaleless (Holton 2003).
Summary of Observations Submitted for Montana
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Spawning magrations are tied closely with the timing of spring highwater.
Habitat includes slow or quiet waters of large rivers or impoundments. They spawn on the gravel bars of large rivers during spring high water. Paddlefish tolerate, or perhaps seek, turbid water (Holton 2003).
Young-of-year paddlefish will "bite" at small food particles, but eventually (within a year) switch to filtering for food as they grow and need more food. The young paddlefish are pale, nearly transparent, and swim in loose groups, preferring to feed on a large zooplankton called Leptodora kindtii (AFS website 2003).
When feeding, adult paddlefish swim with their mouths wide open and filter the zooplankton from the water with filament-like gill rakers. In some places, adult paddlefish also filter aquatic insects and, occasionally, tiny fish. Recent research has shown conclusively that the paddle is an electrosensory structure that functions much like an antenna. It detects weak electric fields. The paddle, head and gill flaps are covered with tiny sensory pores that it uses to detect food organisms. The paddle may also function to keep the fish level in the water while it is continually moving and feeding. The paddle would then provide "lift" much like airplane wings to keep the fish from nose-diving to the bottom (AFS website 2003).
The paddle is not developed at all on very young fish, but by the time the fish reaches 8 inches, the paddle may be half the total length of the fish. As the fish gets larger, the paddle becomes relatively shorter compared to the total length of the fish. Adult paddlefish can live without a paddle, but there is some evidence that the fish that have lost their paddles feed less efficiently and are thinner than those with their paddles intact (AFS website 2003).
Most of the large fish (40 to 90 pounds) at Intake are females which range from 15 to 50 years of age and average about 26 years. Most of the small fish (10 to 40 pounds) are males that range from 9 to 50 years old and average about 16 years. Paddlefish can occasionally live past age 50, with fish in the Yellowstone and upper Missouri River living longer than those farther south (AFS website 2003).
The Montana record is 142 1/2 pounds, caught above Fort Peck, in 1973. Fish of the Yellowstone-Sakakawea stock seldom exceed 100 pounds. Fish living in lakes and reservoirs often grow faster and larger than those living solely in rivers (AFS website 2003).
When paddlefish mature, at about age 9 to 10 for males and age 16 to 17 for females, they migrate up river to spawn. Adult fish do not as a rule die after spawning, but we know from tagging studies that a given female only spawns about every 3 years, and a given male about every 2 years (AFS website 2003).
The males and females have evolved different strategies for reproducing and passing on their genes to the next generation. The larger a female is, the more eggs she can produce, and the more young paddlefish she will probably produce. A male gains less by becoming large because even a small male will have millions of sperm--enough to fertilize all of the eggs from the largest female. It is preferable for males to mature at a younger age than females so they may reproduce more often, as opposed to taking the time to grow large, risking death before they spawn. Conversely, a female benefits more from the gamble she takes in delaying maturity because of the additional eggs she will produce (AFS website 2003).
Paddlefish spawn in rivers during high water periods in late spring or early summer (May to June). In the Yellowstone River, most evidence indicates that downriver areas near Sidney and Fairview are primary spawning areas, and to a lesser extent farther upriver toward Intake. Many spawning sites are not yet well identified, however, and paddlefish undoubtedly spawn over gravel bars and areas of finer substrate in several areas of the Yellowstone River (AFS website 2003).
Paddlefish stocks in Montana are adequate to support a recreational fishery. Current research and monitoring are designed to prevent over-harvest and insure a sustainable wild fishery. Managers accurately estimate the ages of the fish caught in the fisheries. Changes in the age structure of the population are being monitored to insure that young fish are added, and old fish retained, in the populations (AFS website 2003).
The aging of the population, along with decline in fishing success rates and higher harvest of tagged (adult) paddlefish account for the reduction of the paddlefish limit from two per person per year to one per person per year in both Montana and North Dakota, and the proposed reduction to a 1,000 fish annual harvest cap per state. The aim is to stabilize the population at 30,000 fish and avoid over-harvest of this unique, slowly-maturing species. With a fish like paddlefish that matures at an old age, has a record of reproductive problems, and is not seen often until it is large and on its upstream migration, we need to watch constantly for signs of over-harvest (AFS website 2003).
The Yellowstone-Sakakawea stock does not recognize state boundaries. For this reason, management of the stock occurs under a Cooperative Management Plan between the Montana Department of Fish, Wildlife and Parks and the North Dakota Game and Fish Department (AFS website 2003).
- Additional ReferencesLegend: View WorldCat Record View Online Publication
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- American Fisheries Society (AFS), Montana Chapter Website.
- Additional Sources of Information Related to "Fish"