Show simple item record

dc.contributor.authorHayes, Christopher Glennen_US
dc.date.accessioned2014-03-14T20:30:56Z
dc.date.available2014-03-14T20:30:56Z
dc.date.issued2007-12-14en_US
dc.identifier.otheretd-01182008-105214en_US
dc.identifier.urihttp://hdl.handle.net/10919/30989
dc.description.abstractThree hammerhead sharks (Sphyrna spp.) are currently managed as part of the large coastal shark complex in the United States. Including multiple species in an assessment ignores the different stock dynamics of each individual species within the complex due to different life histories. This study completed individual assessments of scalloped (S. lewini), great (S. mokarran), and smooth (S. zygaena) hammerhead sharks in the U.S. Atlantic Ocean and Gulf of Mexico. Combined data for all three species and unclassified hammerhead sharks were also used to produce a stock assessment of the hammerhead shark complex. Depletions of 83%, 96%, and 91% were estimated for scalloped, great, and smooth hammerhead sharks, respectively, between 1981 and 2005. When modeled as a single stock, the hammerhead shark complex experienced a 90% decline over the same time period. All three stocks, and the complex were overfished (below population size associated with maximum sustainable yield (MSY)), and overfishing (fishing level above that associated with MSY) occurred in 2005. We found that scalloped hammerhead shark population recovery is likely to occur within 10 years if catch remains at or below 2005 levels. Great and smooth hammerhead sharks will likely still be overfished in 30 years unless catches are reduced. It appears that the species composition could be changing in this hammerhead shark complex. The faster-growing scalloped hammerhead sharks are able to withstand fishing pressure better than great or smooth hammerhead sharks. However, it is difficult to target any single large coastal shark species while fishing; hence they are subject to similar fishing pressure. The result is a greater decline in great and smooth hammerhead sharks than experienced by scalloped hammerhead sharks. Therefore, the proportion of scalloped hammerhead sharks increased between 1981 and 2005. Species-specific stock assessments, such as those presented here, allow managers to more closely monitor populations of slower-growing species and reduce the risk of overexploitation of those species.en_US
dc.publisherVirginia Techen_US
dc.relation.haspartHayes_Thesis_FINAL.pdfen_US
dc.rightsI hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Virginia Tech or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.en_US
dc.subjecthammerhead sharksen_US
dc.subjectSphyrnaen_US
dc.subjectstock assessmenten_US
dc.subjectmulti-speciesen_US
dc.subjectproduction modelen_US
dc.subjectpopulation dynamicsen_US
dc.titleInvestigating single and multiple species fisheries management: stock status evaluation of hammerhead (Sphyrna spp.) sharks in the western North Atlantic Ocean and Gulf of Mexico.en_US
dc.typeThesisen_US
dc.contributor.departmentFisheries and Wildlife Sciencesen_US
dc.description.degreeMaster of Scienceen_US
thesis.degree.nameMaster of Scienceen_US
thesis.degree.levelmastersen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineFisheries and Wildlife Sciencesen_US
dc.contributor.committeechairJiao, Yanen_US
dc.contributor.committeememberBerkson, James M.en_US
dc.contributor.committeememberCorttes, Enricen_US
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-01182008-105214/en_US
dc.date.sdate2008-01-18en_US
dc.date.rdate2009-02-07
dc.date.adate2008-02-07en_US


Files in this item

Thumbnail

This item appears in the following Collection(s)

Show simple item record