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Document Type

Thesis - University Access Only

Award Date

2010

Degree Name

Master of Science (MS)

Department

Wildlife and Fisheries Science

First Advisor

Brian D.S. Graeb

Abstract

Paddlefish Polyodon spathula provide recreational and commercial angling opportunities throughout much of their range. In the past 100 years, however, paddlefish populations have declined throughout their range. The construction of dams has been identified as a leading cause of population declines, as dams block spawning migrations, alter historic spawning habitats, and disrupt spawning cues. Lake Francis Case, South Dakota, a Missouri River reservoir, supported a paddlefish sport fishery shortly after impoundment but this fishery was closed due to a lack of natural recruitment. Lake Francis Case has been stocked intermittently since 1974, and annually since 1990 to maintain a broodstock population and potentially support a sport fishery. Currently, information necessary for effective management of this population (i.e., age and size structures, recruitment, growth, mortality, stocking success, and sampling methodology) is lacking. The objectives of this study were to 1) determine the historic and current status of paddlefish in Lake Francis Case, and 2) evaluate sampling efficiency and methodology for paddlefish in Lake Francis Case. To evaluate the current status of the Lake Francis Case population, I conducted a population assessment to characterize the population and estimate population dynamics. I then used this information to evaluate the potential effects of a sport fishery on this population. Stockings have successfully maintained this population, as 95 % of fish aged originated following the implementation of advance fingerling stocking in 1990. Natural mortality of stocked fish was low (annual rate = 14.4 %), indicating that conditions were favorable for these fish to be long-lived and attain large sizes. Variability in year-class strength of stocked fish was most likely due to downstream emigration. I hypothesize that emigration was related to water temperature, as year-class strength was negatively correlated to water temperature inputs from Big Bend Dam. Broodstock was reduced over 30 % by 5 % exploitation under simulated 660-mm and 840-mm minimum length regulations. Concomitantly, only 16 % of broodstock was lost under a simulated 1016-mm minimum length limit at 5 % exploitation. These results suggest that this population could support a limited sport fishery (< 5 % exploitation) under a 1016-mm minimum length limit without causing substantial changes to size structure or the availability of broodstock. To evaluate the historic status of paddlefish in Lake Francis Case, I analyzed a 33-year mark-recapture database to examine the effects of sport harvest on paddlefish survival. I also analyzed 27 years of mark-recapture data to evaluate the effects of sport fishery regulations (i.e., creel, quota, season length) on paddlefish survival in the sport fishery below Gavins Point Dam, Nebraska - South Dakota. Additive mortality received substantially more support than compensatory mortality in Lake Francis Case, and survival estimates increased from 78 % to 87 % following closure of the Lake Francis Case sport fishery. I hypothesize that riverine populations are better able to compensate for harvest mortality by reducing natural mortality because they typically have higher natural mortality rates than reservoir populations. Regulations changes below Gavins Point Dam had a negligible effect on survival, and apparent survival was estimated to be 65 % throughout this study. Abiotic factors likely had a greater effect on harvest than regulations below Gavins Point Dam. Although my modeling indicated that regulations had a negligible effect on survival, regulations can prevent overharvest during years of high vulnerability to harvest. I recommend the use of a combination of season length restrictions and a quota or permit system to manage paddlefish sport fisheries throughout the species‘ range. To evaluate sampling efficiency and methodology for paddlefish in Lake Francis Case, I examined the effects of mesh size, sampling location, and season on catch per unit effort (CPUE) and length of paddlefish collected with short-term gill nets. I collected 236 paddlefish during 2008 and 2009. Mean transformed CPUE was higher in spring than in summer, but was similar between mesh sizes and sample sites. The median length of fish captured differed by mesh size, season, and location. The 152-mm bar mesh collected slightly larger fish than the 89-mm mesh. The largest and smallest individuals were collected at the primary tributary (i.e., White River) and its confluence, but only a portion of the population (individuals between 1,000 mm and 1,200 mm) were collected below Big Bend Dam. The length of fish captured increased from spring to summer. I recommend that 89-mm bar mesh be used to collect paddlefish for population assessments, whereas broodstock collections may benefit from the use of larger (e.g., 152-mm) mesh sizes. To collect a wide length range of the population, I recommend that population assessments be conducted at primary tributaries during the spring and summer.

Library of Congress Subject Headings

Paddlefish -- South Dakota -- Francis Case, Lake

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

120

Publisher

South Dakota State University

Rights

Copyright © 2010 Landon Lee Pierce. All rights reserved.

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