SynopsisScaphirhynchus albus and S. platorynchus were studied in Missouri during [1978][1979] to assess their distribution and abundance, to obtain information on their life histories, and to identify existing or potential threats to their survival. S. platorynchus was collected in substantial numbers (4355 specimens) at all 12 sampling stations in the Missouri and Mississippi rivers, while only 11 S. albus were captured from 6 stations. Twelve specimens identified in the field as hybrids between the two species were captured from 4 stations. Morphometric and meristic comparisons of presumed hybrids with the parent species, using cluster and principal components analyses, demonstrated intermediacy of most specimens identified in the field as hybrids. Aquatic insects comprised most of the diet of S. platorynchus and S. albw, but S. albus and the hybrids had consumed considerable quantities of fish. S. albus grew more rapidly than S. platorynchus, while the growth of hybrids was intermediate. Hybridization appears to be a recent phenomenon, resulting from man-caused changes in the big-river environment. Hybridization may be a threat to survival of S. albus in the study streams.

Paddlefish fisheries in some states have become increasingly important, but in other states populations have declined severely and the species range has been reduced. Commercial paddlefish harvests today come mainly from the impounded Tennessee, Mississippi, and Arkansas Rivers. Sport fisheries have replaced commercial fisheries in some areas and even though they are extremely localized, they account for sizable harvests. Declining paddlefish populations reported in several states are a result of loss of spawning habitat. Recent studies in these and other states have increased our knowledge about the paddlefish and its management. Identification and protection of spawning areas is critical to the maintenance of the fisheries.

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