Title page for ETD etd-08122010-063252

Type of Document Dissertation
Author Leaf, Robert Thomas
Author's Email Address rleaf@vt.edu
URN etd-08122010-063252
Title The Evolutionary Effects of Fishing: Implications for Stock Management and Rebuilding
Degree PhD
Department Fisheries and Wildlife Sciences
Advisory Committee
Advisor Name Title
Jiao, Yan Committee Chair
Berkson, James M. Committee Member
Hallerman, Eric M. Committee Member
Murphy, Brian R. Committee Member
Prager, Michael H. Committee Member
  • Keywords: Japanese medaka
  • Oryzias latipes
  • aquaculture
  • life-history evolution
  • quantitative genetics
  • heritability
  • individual-based model
  • fishery-induced evolution
Date of Defense 2010-06-22
Availability unrestricted
Recent empirical studies have demonstrated inter-generational morphological and life-history

changes in fish stocks that have been impacted by size-selective harvest. Evolutionary processes

in biological populations occur through differential survival and reproductive success based, in

part, upon individual phenotypic variability. Fishing is a source of directional selection resulting

in the directed removal of some phenotypes; however, many aspects of the evolutionary effects

of fishing remain have yet to be described. In order to better understand the life-history and

morphological changes that occur as a result of size-selective fishing, and their effect on fishery

dynamics, I first determined the suitability of Japanese medaka (Oryzias latipes) for selection

experiments. I performed selection experiments using Japanese medaka and report how

morphology and life-history characteristics changed over multiple generations of selection. I

then used these patterns of change in life-history and morphology to validate individual-based

simulation candidate models to test general mechanisms of life-history relationships. Finally, I

applied the individual-based simulation modeling approach in order to describe how biological

and fishery characteristics change in a large, age-structured population exposed to size-selective

fishing over multiple generations. I found that the Japanese medaka has attractive characteristics

for biological investigation. The selection experiments indicated large changes in the age-atmaturity,

including a nearly 50% decrease over four generations in the most intense sizeselective

removal regimes. However, I did not observe significant changes in length-at-age or

weight-at-age over the course of the experiment. Candidate simulation models were poor at

predicting some aspects of the life-history characteristics of Japanese medaka. The simulation

model to determine fishery characteristics predicted large decreases in yield and egg production

as a result of decreases in length-at-age. Understanding the relationships of life-history

characteristics and their role in determining population resilience is a step toward understanding

the importance of evolutionary processes in fishery management.

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