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Document Type

Thesis - University Access Only

Award Date

2006

Degree Name

Master of Science (MS)

Department

Wildlife and Fisheries Science

First Advisor

David W. Willis

Abstract

Many state and federal agencies are actively trying to recover the currently endangered pallid sturgeon Scaphirhynchus albus. Efforts have been made to stock hatchery-reared juvenile pallid sturgeon (HRJPS) throughout the Missouri River to help facilitate recovery and long-term monitoring programs were established to evaluate sturgeon populations and the associated fish community. However, there is limited knowledge on how and when to effectively sample for juvenile pallid sturgeon. I compared the effectiveness of passive gill nets, hoop nets, set lines, and drifted trammel nets and towed beam trawls to develop criteria to best determine the mean catch per unit effort (CPUE) for juvenile pallid sturgeon based on selectivity and seasonal efficiency in various habitats of the Missouri River below Fort Randall Dam, South Dakota from April to November in 2003 and 2004. Passive integrated transponder (PIT), elastomer, or a dangler tag identified all pallid sturgeon captured as HRJPS. I captured 18 HRJPS in a total of 300 overnight gill net sets, 37 HRJPS in a total of 707 trammel nets, and 19 HRJPS on 1,299 set lines baited with earthworms Lumbriscus terrrestris. No HRJPS were captured in 515 beam trawl tows, 360 overnight hoop net sets, or on 224 set lines baited with leeches Nephelopsis obscura. Coefficient of variation (CV = 100 X SD/mean) on the monthly mean CPUE values ranged from 324 to 670 for gill nets, 263 to 949 for trammel nets, and 508 to 1630 for set lines. Seasonal trends in mean CPUE were found as the relative precision was the greatest in October for gill nets and in April for trammel nets and set lines. A higher proportion of HRJPS captures for gill nets were in the inside bend of the river that generally is associated with lower water velocities, trammel nets over sandy substrate and in the outside bends that are associated with higher water velocities and greater depths, and for set lines in lower water velocities. Although I found trends among seasons and habitats for gill nets, trammel nets, and set lines, the catch rates were low and annual point estimates of relative abundance are not adequate to detect changes in relative abundance of HRJPS in this reach of the Missouri River. No significant differences were found in length frequency distributions of HRJPS captured among gill nets, trammel nets, and set lines, but low sample sizes resulted in low power (1-!) for such analyses. A greater number of HRJPS were captured in the smaller gill net mesh (" 3.81 cm bar mesh) and HRJPS captured in the larger mesh sizes (# 5.08 cm bar mesh) were generally longer. A greater number and longer HRJPS were captured on the 10/0 circle hook compared to the 12/0 circle hook used on set lines. Further research is needed to verify my results with specific objectives to find the most appropriate time and habits to adequately sample for HRJPS. Further research is needed to explore different variations of the gears I used in my study. Different twine colors in gill and trammel nets, size and styles of hooks and baits used on set lines, and variations of the benthic trawl may be more effective at capturing juvenile pallid sturgeon. Fort Randall Dam has created a highly regulated environment with flows fluctuating widely, both seasonally and daily, with reduced temperatures and turbidity affecting growth of native fish populations, including the pallid sturgeon and the sympatric shovelnose sturgeon Scaphirhynchus platorynchus. Hatchery-reared juvenile pallid sturgeon have been released in this reach of the Missouri River since 2000. However, biologists do not know whether this stretch of river can sustain a viable population of pallid sturgeon. The objectives of this component of my study were to determine the growth of HRJPS among year classes and among family crosses and to determine the condition of HRJPS and shovelnose in this reach of the Missouri River. Growth and condition was used as a tool to evaluate the suitability of this reach of the Missouri River for continued stocking efforts. The mean growth rates were greater for HRJPS " age 3 compared to HRJPS # age 4. Mean relative condition (Kn) at stocking was similar among all year classes even though HRJPS were released at different ages and times of the year. Mean Kn decreased for nearly all HRJPS from time of stocking to recapture. The decline in mean Kn from time of stocking to recapture is likely due to the rigors of living with high water velocities, variable temperatures, and variable prey availability compared to living in the controlled environment of a fish hatchery. The 1997 and 1998 year classes had significantly lower mean Kn compared to the 1999, 2000, and 2001 year classes at recapture. No significant differences were found in the mean growth rates or Kn among five family crosses in the 1997 year class. However, mean Kn of two family crosses in the 1999 year class were different at stocking, but were eventually similar at recapture. The family cross with the highest mean Kn did grow significantly faster in length. Environmental conditions likely played a large role in their Kn. Seasonal differences in mean relative weight (Wr) were found for shovelnose sturgeon in this reach of the Missouri River. Mean Wr in shovelnose sturgeon peaked in June during the spawning period and declined throughout the summer. Mean Wr of shovelnose sturgeon captured below the Niobrara River confluence, which is characterized by a greater number of sand bars and an increase in turbidity and temperature, was higher than shovelnose sturgeon captured above the confluence. This result may be due to an increase in the availability of prey below the confluence. Mean Wr declined as shovelnose sturgeon attained greater lengths which has also been reported for other shovelnose sturgeon populations throughout the Missouri River. The early life history of the pallid sturgeon is not completely understood. This is especially true due to low abundance resulting from no recruitment in the river above Gavins Point Dam for more than 40 years. The more abundant shovelnose sturgeon has been considered a surrogate species to the pallid sturgeon. The objectives of this component of my study were to determine the seasonal food habits and diet overlap between HRJPS and adult shovelnose sturgeon in the Missouri River below Fort Randall Dam. Additionally, the information gained from this study will provide the baseline data for bioenergetics models for juvenile pallid sturgeon. Seasonal trends in the diets of HRJPS and adult shovelnose sturgeon were found with Chironomidae in the greatest numbers and dry weights during early summer, Ephemeroptera during the late summer, and Trichoptera in the early spring and late fall. However, the highest mean numbers and dry weights of each prey type consumed by HRJPS and shovelnose sturgeon always occurred in different months between the two sturgeon species. Diet overlap between HRJPS and adult shovelnose sturgeon was low with a Schoener index (0 = no overlap and 1 = complete overlap) of 0.53 in 2003 and 0.21 in 2004. Hatcheryreared juvenile pallid sturgeon consumed a greater proportion of fish in 2003 and Ephemeroptera in 2004 compared to shovelnose sturgeon. Shovelnose sturgeon consumed a greater proportion of Chironomidae in both years compared to HRJPS. I found no differences between fork length groups in the mean numbers and dry weights of prey types for HRJPS and shovelnose sturgeon even though both sturgeon were found to have lower condition as they attained greater lengths. However, HRJPS generally consumed more fish and Isopoda as they attained greater lengths. The low turbidity, an abundance of piscivorous fish, and lack of recruitment of native benthic cyprinids in this stretch of the Missouri River may have detrimental affects on the ability of HRJPS to forage for fish. This study provided a better understanding of the diet of HRJPS in this reach of the Missouri River and will provide valuable information for bioenergetics research on pallid sturgeon.

Library of Congress Subject Headings

Sturgeons -- Missouri River
Sturgeons -- South Dakota
Sturgeons --Food -- Missouri River
Sturgeons --Food South Dakota

Description

Includes bibliographical references (page 140-153)

Format

application/pdf

Number of Pages

175

Publisher

South Dakota State University

Rights

Copyright © 2006 Greg Wanner. All rights reserved.

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