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dc.contributor.authorJordaan, Gareth L.
dc.contributor.authorSantos, Jorge
dc.contributor.authorGroeneveld, Johan C.
dc.date.accessioned2019-02-13T12:02:17Z
dc.date.available2019-02-13T12:02:17Z
dc.date.issued2018-10-24
dc.description.abstractThe assumption of a proportional relationship between catch-per-unit-effort (CPUE) and the abundance of sharks caught by pelagic longliners is tenuous when based on fisher logbooks that report only retained specimens. Nevertheless, commercial logbooks and landings statistics are often the only data available for stock status assessments. Logbook data collected from local and foreign pelagic longline vessels operating in four areas off southern Africa between 2000 and 2015 were used to construct standardized CPUE indices for blue sharks <i>Prionace glauca</i> and shortfin makos <i>Isurus oxyrinchus</i>. Generalized linear mixed models were used to explore the effects of year, month, vessel, fleet and presence of an observer on blue shark and shortfin mako variability. Landing statistics and auxiliary information on the history of the fishery, regulation changes, and market factors were superimposed on the CPUE indices, to test hypotheses that they would influence CPUE trends. Indices in the West and Southwest (Atlantic) areas were elevated for both species, compared to the South and East (Indian Ocean). The scale of year-on-year CPUE increments, up to an order of magnitude for blue sharks, reflected occasional targeting and retention, interspersed with periods where blue sharks were not caught, or discarded and not reported. Increments were smaller for higher value shortfin makos, suggesting that indices were less affected by unreported discarding. CPUE indices and landings of both shark species have increased in recent years, suggesting increased importance as target species. Analysis of logbook data resulted in unreliable indicators of shark abundance, but when trends were interpreted in conjunction with landings data, disaggregated by area and month, and with hindsight of market demand and regulation changes, anomalies could be explained.en_US
dc.description.sponsorshipNational Research Foundation The University of KwaZulu Natalen_US
dc.descriptionSource at <a href=https://doi.org/10.7717/peerj.5726> https://doi.org/10.7717/peerj.5726</a>. Licensed <a href=http://creativecommons.org/licenses/by-nc-nd/4.0/> CC BY-NC-ND 4.0.</a>en_US
dc.identifier.citationJordaan, G.L., Santos, J. & Groeneveld, J.C. (2018). Effects of inconsistent reporting, regulation changes and market demand on abundance indices of sharks caught by pelagic longliners off southern Africa. <i>PeerJ</i>, (10). https://doi.org/10.7717/peerj.5726en_US
dc.identifier.cristinIDFRIDAID 1628456
dc.identifier.doi10.7717/peerj.5726
dc.identifier.issn2167-8359
dc.identifier.urihttps://hdl.handle.net/10037/14686
dc.language.isoengen_US
dc.publisherPeerJen_US
dc.relation.journalPeerJ
dc.rights.accessRightsopenAccessen_US
dc.subjectVDP::Agriculture and fishery disciplines: 900::Fisheries science: 920en_US
dc.subjectVDP::Landbruks- og Fiskerifag: 900::Fiskerifag: 920en_US
dc.subjectFishery managementen_US
dc.subjectPelagic longlineen_US
dc.subjectPelagic sharksen_US
dc.subjectRetained bycatchen_US
dc.subjectReportingen_US
dc.subjectRegulationsen_US
dc.titleEffects of inconsistent reporting, regulation changes and market demand on abundance indices of sharks caught by pelagic longliners off southern Africaen_US
dc.typeJournal articleen_US
dc.typeTidsskriftartikkelen_US
dc.typePeer revieweden_US


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