Date Awarded

2020

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Virginia Institute of Marine Science

Advisor

Jan R McDowell

Committee Member

Eric J Hilton

Committee Member

Carl T Friedrichs

Committee Member

Christian M Jones

Abstract

The Clearnose Skate (Rostroraja eglanteria, Bosc 1800) is a flat, benthic elasmobranch and member of the family Rajidae. They are widely distributed in the coastal waters of the east coast of the United States and in the northeastern Gulf of Mexico. It has been noted that the physical appearance of Clearnose Skate from the southern end of their range near South Carolina is distinct from individuals found in the northern end of their range near Woods Hole, MA, perhaps suggestive of a sub-species, though this observation has not been further investigated. Clearnose Skate are seasonally migratory and are often incidentally caught in bottom trawl fisheries during times of migration and congregation, discarded at sea, and poorly accounted for in catch records. They are managed by the New England Fishery Management Council (NEFMC) as part of a skate complex, which includes six other species of skate, and are not currently managed by the Southeast Fishery Management Council or the Gulf States Fishery Management Council. Continuing to indiscriminately harvest an undermanaged species without knowledge of the underlying population structure can have deleterious effects on scientific, conservation, and management efforts. This study used an interdisciplinary combination of molecular and morphological techniques to better understand the population structure of the Clearnose Skate sampled throughout their geographic range. Specimens were collected by fisheries-independent surveys and categorized into one of three study regions; U.S. East Coast north of Cape Hatteras (NOR), U.S. East Coast from Cape Hatteras to Florida (SOU), and the Gulf of Mexico (GOM). For genetic studies, DNA was extracted from 194 specimens (NOR = 127, SOU = 45, GOM = 22) and shipped to Diversity Arrays Technology for high-throughput genotyping-by-sequencing, resulting in a final filtered dataset of 8,914 loci (outlier and neutral) and 30 outlier loci. For morphological studies, 126 specimens (NOR =57, SOU = 47, GOM = 24) were used to collect 41 morphometric, 9 thorn, and 7 skeletal characters. Results of both genetic and morphological analyses indicate that GOM specimens are distinct from those collected off the U.S East Coast and should be managed as a separate population. This study was unable to definitively resolve whether structure was present in samples collected along the U.S. east coast, but genetic data indicated small but significant differences between samples collected in the South Carolina, Georgia, and Florida region as compared to samples collected from more northern regions based on pairwise FST values. These genetic differences were spatially autocorrelated, indicating a genetic gradient along the East Coast consistent with an isolation-by-distance model. Before management recommendations in this region can be made, more information regarding Clearnose Skate migration and reproduction are needed.

DOI

http://dx.doi.org/10.25773/v5-bphs-y255

Rights

© The Author

Available for download on Sunday, December 11, 2022

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Genetics Commons

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