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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Wildlife and Fisheries Science

First Advisor

David W. Willis


Bluegill Lepomis macrochirus reproductive biology was evaluated in two Nebraska Sandhill lakes, 323-ha Pelican Lake in Cherry County and 38-ha Cozad Lake in Brown County, during 1998. Catch per unit effort of stock-length bluegills in trap nets did not differ between lakes (P=0.19). Proportional stock density was significantly higher (P<0.01) in Cozad Lake but relative stock density of preferred-length bluegills was higher (P<0.01) in Pelican Lake. Pelican Lake contained a fast-growing bluegill population (211 mm total length at age 5), while Cozad Lake bluegills had a moderate growth rate (174 mm at age 5). Condition (indexed with relative weight; Wr) of bluegills increased with increasing fish length at Pelican Lake, but not at Cozad Lake. Mean Wr of quality-length and longer bluegills was lower (P<0.01) in Cozad Lake, possibly due to intraspecific and interspecific competition for lower prey abundance (e.g., total zooplankton abundance substantially lower in Cozad Lake). Gonadosomatic index (GS!) values were determined from samples collected within a 3-d period at the two lakes during late May. Mean female bluegill GS! was significantly higher (P<0.01) at Pelican Lake (12.1%) than at Cozad Lake (9.6%). Mean GS! for male bluegills from 115 to 149 mm (the smallest length group tested) was significantly lower (P<0.01) in Cozad Lake than mean GS! for larger male bluegills. Mean GS! of 115- to 149-mm male bluegills in Pelican Lake was significantly lower than mean GS! of quality- to preferred- and memorable- to trophy-length males (P<0.02 for both) but was not different than mean GS! of preferred- to memorable-length males (P=0.23). Additionally, the mean GS! for male bluegills of the smallest length group in Cozad Lake was significantly lower (P<0.01} than mean GS! for the equivalent length group in Pelican Lake. Mature female bluegills in both lakes exhibited multiple-spawning capabilities as evidenced by multiple egg diameter modes within the ovaries. ovaries of the longest length group of female bluegills in Cozad Lake contained a lower percentage of mature eggs and lower condition, possibly indicating that those fish were limited by low food resources. Modal diameters for the largest clutch of eggs increased with increasing fish length at Pelican Lake. Larval bluegills were collected at approximately 2-week intervals throughout the spawning period with an ichthyoplankton trawl (0.75-m diameter, 500-μm mesh) at both lakes. Larvae were first collected on 5 June in Cozad Lake and on 25 June in Pelican Lake. Peak abundance of larvae <13 mm in length occurred approximately four weeks apart in each lake and was 12.5/m3 in Cozad Lake, and 15.8/m3 in Pelican Lake. Spawning duration was apparently extended (i.e., approximately 7 weeks) at Cozad Lake, but quite brief at Pelican Lake. Eight Nebraska Sandhill lakes were sampled for incidence of cuckoldry by trap-net sampling and electrof ishing conducted during the 1998 and 1999 bluegill spawning seasons. Of the many attributes tested at these lakes, only two were different (P~0.05) between lake types (i.e., cuckolders present and cuckolders absent). Relative stock density of preferred-length largemouth bass Micropterus salmoides was higher {P<0.01) in lakes where cuckolders were present. A largemouth bass population exhibiting high size structure could be indicative of low abundance and little predation on bluegill, including those slower-growing bluegills that may be following the cuckolder life history. Total vegetation coverage {e.g., emergent and submergent combined) was higher {P=0.01) in lakes where cuckolders were not collected, perhaps because of differences between the two cuckolder strategies of female mimicry and sneaking. Mimicry can be advantageous in a vegetated or non-vegetated environment while bluegill sneakers are probably more limited to vegetated environments where ample concealment cover is present.

Library of Congress Subject Headings

Fish populations--Nebraska--Sandhills


Includes bibliographical references (pages 69-74)



Number of Pages



South Dakota State University


Copyright ©2007 Jamie M. Chronert. All rights reserved.