Investigating single and multiple species fisheries management: stock status evaluation of hammerhead (Sphyrna spp.) sharks in the western North Atlantic Ocean and Gulf of Mexico

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dc.contributor.authorHayes, Christopher Glennen
dc.contributor.committeechairJiao, Yanen
dc.contributor.committeememberBerkson, James M.en
dc.contributor.committeememberCorttes, Enricen
dc.contributor.departmentFisheries and Wildlife Sciencesen
dc.date.accessioned2014-03-14T20:30:56Zen
dc.date.adate2008-02-07en
dc.date.available2014-03-14T20:30:56Zen
dc.date.issued2007-12-14en
dc.date.rdate2009-02-07en
dc.date.sdate2008-01-18en
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
dc.description.degreeMaster of Scienceen
dc.identifier.otheretd-01182008-105214en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-01182008-105214/en
dc.identifier.urihttp://hdl.handle.net/10919/30989en
dc.publisherVirginia Techen
dc.relation.haspartHayes_Thesis_FINAL.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjecthammerhead sharksen
dc.subjectSphyrnaen
dc.subjectstock assessmenten
dc.subjectmulti-speciesen
dc.subjectproduction modelen
dc.subjectpopulation dynamicsen
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 Mexicoen
dc.typeThesisen
thesis.degree.disciplineFisheries and Wildlife Sciencesen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.levelmastersen
thesis.degree.nameMaster of Scienceen

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