The Status of Nebraska Fishes in the Missouri River. 1. Paddlefish (Polyodontidae: Polyodon spathula)

Authors

Larry W. Hesse, Nebraska Game and Parks Commission
Gerald E. Mestl, Nebraska Game and Parks Commission

Date of this Version

1993

Comments

1993. Transactions of the Nebraska Academy of Sciences, XX: 53-65. Copyright © 1993 Hesse and Mestl.

Abstract

The mean larval paddlefish density was 60 times higher in the upper unchannelized section of the Missouri River in Nebraska compared to the lower unchannelized section, and was three times higher than the channelized section's density. Within the upper unchannelized section, 96.2% of the larvae were collected in the discharge of two tributaries, which lie in the lower one-third of the reach. Survival from larval to young-of-the-year stage (June through August) was highest during 1991 due, in part, to the recent drought. Reduced fluctuation of river stages occurred as a result of reduced runoff, which minimized the need to reduce discharge to prevent flooding in the lower basin. The mean weight of paddlefish captured during the 1991 snagging season increased from 6.89 kg in 1990 to 7.45 kg, while the mean length increased from 739 mm (eye-to-fork length) to 753 mm. The percentage of snagged paddlefish 10 years old or older decreased from 15.3% in 1990 to 9.5% in 1991. When we compared the mean length of snagged paddlefish with the mean length of gillnet-captured paddlefish from tailwater and downriver sites there was no difference as demonstrated by t-test. There was a significant difference (P_t < 0.01) between mean weights. The same relationship regarding length and weight was true when fish gillnetted downriver was compared to fish gillnetted in the tailwater (P_t < 0.0001). These data suggest that larger, sexually mature fish are congregated in the tailwater of Gavins Point Dam, which is a total barrier to fish migration. The quota of 1,600 fish was exceeded in 1989 and 1990 but was not reached in the 1991 or 1992 seasons, which extended the full 30 days. In the Gavins Point Dam tailwater area, total annual man-hours of fishing was up from 5,339 hours in 1990 to 8,563 hours in 1991 and 9,139 hours in 1992. Mean catch rate for 1991 was 0.1 fish per hour of snagging compared with 0.33 fish per hour in 1990; however, catch rate declined to 0.05 during 1992. A protected slot-length limit was imposed in 1992 and was considered successful because there was no indication of excessive mortality associated with catch and release.