Dissertation/Thesis Abstract

Understanding Population Connectivity in Shortfin Mako Shark (Isurus oxyrinchus) at Multiple Spatial Scales
by Kacev, David, Ph.D., University of California, Davis, 2015, 128; 3723647
Abstract (Summary)

Pelagic sharks are both ecologically and economically valuable as top predators and fishery targets respectively. Their highly migratory nature and cryptic life histories make them logistically difficult to study. Despite their frequent interaction with various global fisheries, they are difficult to effectively manage. Understanding population connectivity across their cosmopolitan distributions, makes international management more likely. Population genetics is a powerful to address questions of functional population connectivity. Allele frequencies can identify interbreeding population segments, but cannot directly identify individual movement. Tagging, on the other hand, monitors the movement of individuals, but is limited in inference by the number of tags applied. Together, using both molecular tools and tag analyses can provide valuable insight into the ecology of traditionally data-poor species. Two of the shark species most impacted by international fisheries are the shortfin mako (Isurus oxyrinchus) and the common thresher (Alopias vulpinus).

In the first chapter of this dissertation, I developed and optimized nuclear microsatellite loci for both mako and thresher sharks. I then used these loci to test for polyandry in a litter of thresher pups. I developed and optimized 11 novel microsatellite loci for use on shortfin mako shark. I also developed and optimized six novel microsatellite loci and successfully cross screened two mako loci for use on common thresher shark. The analysis of a single litter of thresher pups indicates that polyandry is likely in this pelagic shark.

The second chapter focuses on understanding mako population connectivity for makos across the US/Mexico border in the Southern California Bight. To address this question, I use the newly described microsatellite loci and both conventional and archival tag data. Microsatellite analysis across the US/Mexico border indicates that makos in the region comprise a single genetic unit, and both conventional and SPOT tag results corroborate that finding. Temporal effective population size analysis indicates that the Southern California Bight supports a robust and diverse population of mako sharks.

My third chapter looks at mako population connectivity across the entire Pacific Ocean using a combination of nuclear and mitochondrial loci supported by tag analyses. On a larger spatial scale, shortfin mako exhibit barriers to mitochondrial gene flow across the equator and east to west across the south Pacific. Nuclear microsatellites, on the other hand, do not show evidence of spatial structuring with the Pacific Ocean basin. This indicates that makos exhibit gender mediated dispersal on oceanic scales. This pattern is weakly supported by tag recapture analysis.

Indexing (document details)
Advisor: Lewison, Rebecca L., Bohonak, Andrew J.
Commitee: Hyde, John R., Klimley, Peter A., Vetter, Russell D.
School: University of California, Davis
Department: Ecology
School Location: United States -- California
Source: DAI-B 77/02(E), Dissertation Abstracts International
Subjects: Ecology, Biological oceanography
Keywords: Microsatellite, Pelagic, Population genetics, Shark
Publication Number: 3723647
ISBN: 978-1-339-06492-5
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