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 RiverQuestion of the Monthfor Summer 2008Compiled by Jennifer Robertson, M.Ed.RiverQuest Education Specialist
Question:RiverQuest WAVES from June 2008 featured a local teacher who incorporated environmental science into an elaborate art project: his students crafted large model paddlefish. What's a paddlefish? Do we have them in the rivers of Pittsburgh?
Answer:Remnants of pre-historic times, paddlefish (Polyodon spathula) are an unusual looking and elusive species of fish that are native to large river habitats of the Mississippi River Basin in North America. And yes--we have them in the rivers of Pittsburgh.
Remnants of pre-historic times, paddlefish (Polyodon spathula) are an unusual looking and elusive species of fish that are native to large river habitats of the Mississippi River Basin in North America. The bluish-gray fish is almost entirely cartilaginous (they have very little calcified bone) and reach lengths of up to 7 feet, one-third of which is comprised of a flat, paddle-shaped snout called a rostrum. The rostrum is thought to be a sensory organ that enables the filter-feeding fish to locate their prey, primarily microscopic zooplankton, and may also help them to balance. The adult paddlefish’s large mouth contains numerous gill rakers, long sieve-like structures that allow the fish to strain tiny organisms from the water. Paddlefish have been known to reach over 30 years of age, with males reaching sexual maturity at 7-9 years and females at 10-12 years old. Historically, the Allegheny and Ohio Rivers of Pennsylvania (and their large tributaries) were part of the paddlefish’s natural range. During the late 19th and early 20th centuries a number of factors led to the decline and eventual extirpation of paddlefish from Pennsylvania’s waterways. Extirpation, as defined by Argent and Kimmel, is the localized loss of a particular species often in response to some anthropogenic influence. In Pennsylvania’s Ohio River Basin, those influences included poor water quality, the building of locks and dams to canalize the rivers, and the dredging of our rivers. Some effects may be attributed to the over-fishing of paddlefish to help satiate a nation’s need for caviar, prior to the assignment of protected status. Over half of the 26 states in the paddlefish’s range experienced declines in population during the same time period. The last published report of paddlefish naturally occurring in Pennsylvania waters was in 1919. In 1991, after determining that water quality had improved significantly, the Pennsylvania Fish and Boat Commission (PFBC) began a stocking program to restore paddlefish to their historical range in the commonwealth. The goal is to have a self-sustaining population of paddlefish and a possible sport fishery in the future. To date over 130,000 hatchery raised paddlefish fingerlings, each approximately 10-12 inches in total length, have been released into the Ohio and Allegheny Rivers. Sampling done in 2005 and 2006 resulted in the recovery of paddlefish from the Ohio, Allegheny, Monongahela and Kiskiminetas Rivers as well. In 2006, a study was commissioned by the PFBC to determine, in part, if a naturally reproducing paddlefish population exists in the Ohio River Basin. Although it was found that a small number of sexually mature paddlefish capable of reproduction are living in our rivers, there is not yet any evidence of natural reproduction. The most likely barrier (quite literally) to paddlefish reproduction is the canalization of the rivers. Although paddlefish have proven able to navigate the river locks, they still often move large distances to reach suitable spawning habitats. Locks and dams make it more difficult for the fish to reach their spawning grounds, and they alter the river substrate where eggs are lain and fertilized. The dams interrupt the natural flow and can affect the water temperature water that normally acts as a trigger for spawning to occur.
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