Limits to the use of environmental indices to reduce risk and/or increase yield in the South African anchovy fishery

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dc.contributor.authorDe Oliveira, J A A
dc.contributor.authorButterworth, Doug S
dc.date.accessioned2016-03-11T08:49:09Z
dc.date.available2016-03-11T08:49:09Z
dc.date.issued2005
dc.date.updated2016-03-11T08:03:54Z
dc.description.abstractEnvironmental indices that provide short-term predictions of recruitment have the potential to improve the average yield from highly productive resources that sustain recruit fisheries without an associated increase in risk (of resource 'collapse'). This is particularly true for cases where a measurement of recruitment is not available until after substantial fishing on this recruitment has already taken place. The South African anchovy Engraulis encrasicolus resource reflects such a situation, and forms the basis for a simulation study to investigate the benefits of using environmental indices to set appropriate Total Allowable Catches (TACs). Simulations, based on a 'management procedure' (sensu the International Whaling Commission), investigate how such benefits are related to the proportion of variation in recruitment explained by the environmental index. Furthermore, they evaluate to what extent these benefits are compromised by uncertainties related to the degrees of freedom effect (over-fitting data), the selection of explanatory variables (danger of spurious correlations), and errors in the values of explanatory variables (including measurement error). Five recruitment prediction models that incorporate increasing numbers of these uncertainties are investigated. These predictions are used to adjust TACs depending on whether they indicate forthcoming recruitment to be in the top or bottom third of the distribution of possible recruitment values. Results indicate that an environmental index needs to explain roughly 50% or more of the total variation in recruitment (r2 ≥ 0.5) before the management procedure starts showing benefits in terms of the summary performance statistics for risk and average catch. Comparable benefits are possible at a lower r2 value when TAC constraints are removed, but there is then a large associated increase in interannual catch variation. When r2 is low, performance in terms of average catch may prove worse if attempting to take account of an environmental variable in setting the TAC than ignoring it.en_ZA
dc.identifierhttp://dx.doi.org/10.2989/18142320509504078
dc.identifier.apacitationDe Oliveira, J. A. A., & Butterworth, D. S. (2005). Limits to the use of environmental indices to reduce risk and/or increase yield in the South African anchovy fishery. <i>African Journal of Marine Science</i>, http://hdl.handle.net/11427/17628en_ZA
dc.identifier.chicagocitationDe Oliveira, J A A, and Doug S Butterworth "Limits to the use of environmental indices to reduce risk and/or increase yield in the South African anchovy fishery." <i>African Journal of Marine Science</i> (2005) http://hdl.handle.net/11427/17628en_ZA
dc.identifier.citationDe Oliveira, J. A. A., & Butterworth, D. S. (2005). Limits to the use of environmental indices to reduce risk and/or increase yield in the South African anchovy fishery. African Journal of Marine Science, 27(1), 191-203.en_ZA
dc.identifier.issn1814-232Xen_ZA
dc.identifier.ris TY - Journal Article AU - De Oliveira, J A A AU - Butterworth, Doug S AB - Environmental indices that provide short-term predictions of recruitment have the potential to improve the average yield from highly productive resources that sustain recruit fisheries without an associated increase in risk (of resource 'collapse'). This is particularly true for cases where a measurement of recruitment is not available until after substantial fishing on this recruitment has already taken place. The South African anchovy Engraulis encrasicolus resource reflects such a situation, and forms the basis for a simulation study to investigate the benefits of using environmental indices to set appropriate Total Allowable Catches (TACs). Simulations, based on a 'management procedure' (sensu the International Whaling Commission), investigate how such benefits are related to the proportion of variation in recruitment explained by the environmental index. Furthermore, they evaluate to what extent these benefits are compromised by uncertainties related to the degrees of freedom effect (over-fitting data), the selection of explanatory variables (danger of spurious correlations), and errors in the values of explanatory variables (including measurement error). Five recruitment prediction models that incorporate increasing numbers of these uncertainties are investigated. These predictions are used to adjust TACs depending on whether they indicate forthcoming recruitment to be in the top or bottom third of the distribution of possible recruitment values. Results indicate that an environmental index needs to explain roughly 50% or more of the total variation in recruitment (r2 ≥ 0.5) before the management procedure starts showing benefits in terms of the summary performance statistics for risk and average catch. Comparable benefits are possible at a lower r2 value when TAC constraints are removed, but there is then a large associated increase in interannual catch variation. When r2 is low, performance in terms of average catch may prove worse if attempting to take account of an environmental variable in setting the TAC than ignoring it. DA - 2005 DB - OpenUCT DP - University of Cape Town J1 - African Journal of Marine Science LK - https://open.uct.ac.za PB - University of Cape Town PY - 2005 SM - 1814-232X T1 - Limits to the use of environmental indices to reduce risk and/or increase yield in the South African anchovy fishery TI - Limits to the use of environmental indices to reduce risk and/or increase yield in the South African anchovy fishery UR - http://hdl.handle.net/11427/17628 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/17628
dc.identifier.urihttp://www.tandfonline.com/doi/abs/10.2989/18142320509504078
dc.identifier.vancouvercitationDe Oliveira JAA, Butterworth DS. Limits to the use of environmental indices to reduce risk and/or increase yield in the South African anchovy fishery. African Journal of Marine Science. 2005; http://hdl.handle.net/11427/17628.en_ZA
dc.languageengen_ZA
dc.publisherNational Inquiry Services Centreen_ZA
dc.publisher.departmentMarine Resource Assessment and Management Groupen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.sourceAfrican Journal of Marine Scienceen_ZA
dc.source.urihttp://www.tandfonline.com/toc/tams20/current
dc.subject.otherAnchovy
dc.subject.otherEnvironmental indices
dc.subject.otherManagement procedures
dc.subject.otherRecruitment predictions
dc.subject.otherRisk
dc.subject.otherSimulations
dc.subject.otherYield
dc.titleLimits to the use of environmental indices to reduce risk and/or increase yield in the South African anchovy fisheryen_ZA
dc.typeJournal Articleen_ZA
uct.subject.keywordsAnchovyen_ZA
uct.subject.keywordsEnvironmental indicesen_ZA
uct.subject.keywordsManagement proceduresen_ZA
uct.subject.keywordsRecruitment predictionsen_ZA
uct.subject.keywordsRisken_ZA
uct.subject.keywordsSimulationsen_ZA
uct.subject.keywordsYielden_ZA
uct.type.publicationResearchen_ZA
uct.type.resourceArticleen_ZA
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