Rationale for a Harvest Slot Limit for Paddlefish in the Upper Mississippi River

In this paper, data are reviewed on the lengths, weights, and sex of paddlefish Polyodon spathula captured by snagging and by nets from eight pools of the upper Mississippi River in 1975–1978 and by snagging from Pool 13 in 1988. Fisheries were targeted on the largest specimens, which were typically mature females. From 1975 to 1978, only 7 of 315 male fish (2.2%) exceeded 114 cm in fork length, whereas 41 of 288 females (14.2%) exceeded that length. Only two males (0.6%) exceeded 11 years of age, whereas 22 females (7.6%) were older than age 11. Thus, among fish longer than 114 cm, there were 5.9 females harvested for every male, a highly significant difference between the sexes ( P < 0.005). Of the 33 fish sampled in 1988 that exceeded 114 cm in fork length, 28 were females and 5 were males (5.6 females for every male). Although mature females constituted only 5.9% of the fish sampled from the population in 1975–1978, they were the primary spawners, and they are avidly sought and selected for by anglers. To protect large female spawners, rebuild the fishery, and prevent harvest of small paddlefish with substantial growth potential, a harvest slot limit of 57–86 cm for body length (front of eye to fork of tail) or 2.2–11.3 kg for weight is proposed for paddlefish in Iowa's portion of the Mississippi River. Fish larger or smaller than these limits would be protected from harvest. Management considerations include possible alternatives, public acceptance of the regulation, hooking and handling mortality, the need for evaluation and enforcement, and coordination among states.