Age-structured production model assessments and projections including updated parameters to model the intermittent aggregation of Namibian orange roughy

 

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dc.contributor.author Brandão, Anabela
dc.contributor.author Butterworth, Doug S
dc.date.accessioned 2016-03-18T08:20:43Z
dc.date.available 2016-03-18T08:20:43Z
dc.date.issued 2007
dc.identifier.citation Brandão, A., & Butterworth, D. S. (2007). Age-structured production model assessments and projections including updated parameters to model the intermittent aggregation of Namibian orange roughy. Namibian Ministry of Fisheries and Marine Resources document: DWFWG/WkShop/Feb07/Doc, 5. en_ZA
dc.identifier.uri http://hdl.handle.net/11427/17986
dc.description.abstract Updated assessments of the four orange roughy aggregations off Namibia, based upon a maximum penalised likelihood approach which uses all available indices of abundance and reflects the proportion of a stock present at the fishing aggregation each year, are presented, and projections under constant catch levels reported. Further abundance data now available for Frankies allow the parameters of the beta distribution used to reflect the proportion aggregating to spawn each year to be updated. This leads to more optimistic results for stock status, slightly so for Frankies and Rix for which estimates of the ratio of current to preexploration levels increase from the 60%’s to the 70%’s, but substantially so for Johnies which is no longer estimated to be heavily depleted. With no new standardised CPUE values available, Hotspot remains estimated as highly depleted. The range of variable aggregation levels estimated are not qualitatively incompatible with information for Australian orange roughy aggregations. Changing from the earlier to the updated beta distribution parameters increases medium term annual sustainable yield estimates for the resource as a whole from 1 850 to 4 400 tons, though the latter figure needs to be considered with caution as it is particularly dependent on the assumption that the beta distribution estimated for proportions aggregating at Frankies applies also to Johnies. Broadly speaking, MSY estimates at 1 600 to 3 500 tons are some 5–60% more than estimated a year previously. However, the varying proportions of abundance present at aggregations from year to year would lead to difficulties in making a catch of this size every year. en_ZA
dc.language eng en_ZA
dc.title Age-structured production model assessments and projections including updated parameters to model the intermittent aggregation of Namibian orange roughy en_ZA
dc.type Working Paper en_ZA
dc.date.updated 2016-03-18T08:18:51Z
uct.type.publication Research en_ZA
uct.type.resource Research paper en_ZA
dc.publisher.institution University of Cape Town
dc.publisher.faculty Faculty of Science en_ZA
dc.publisher.department Marine Resource Assessment and Management Group en_ZA
dc.identifier.apacitation Brandão, A., & Butterworth, D. S. A. (2007). <i>Age-structured production model assessments and projections including updated parameters to model the intermittent aggregation of Namibian orange roughy</i> University of Cape Town ,Faculty of Science ,Marine Resource Assessment and Management Group. Retrieved from http://hdl.handle.net/11427/17986 en_ZA
dc.identifier.chicagocitation Brandão, Anabela, and Doug S A Butterworth <i>Age-structured production model assessments and projections including updated parameters to model the intermittent aggregation of Namibian orange roughy.</i> University of Cape Town ,Faculty of Science ,Marine Resource Assessment and Management Group, 2007. http://hdl.handle.net/11427/17986 en_ZA
dc.identifier.vancouvercitation Brandão A, Butterworth DSA. Age-structured production model assessments and projections including updated parameters to model the intermittent aggregation of Namibian orange roughy. 2007 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/17986 en_ZA
dc.identifier.ris TY - Working Paper AU - Brandão, Anabela AU - Butterworth, Doug S A AB - Updated assessments of the four orange roughy aggregations off Namibia, based upon a maximum penalised likelihood approach which uses all available indices of abundance and reflects the proportion of a stock present at the fishing aggregation each year, are presented, and projections under constant catch levels reported. Further abundance data now available for Frankies allow the parameters of the beta distribution used to reflect the proportion aggregating to spawn each year to be updated. This leads to more optimistic results for stock status, slightly so for Frankies and Rix for which estimates of the ratio of current to preexploration levels increase from the 60%’s to the 70%’s, but substantially so for Johnies which is no longer estimated to be heavily depleted. With no new standardised CPUE values available, Hotspot remains estimated as highly depleted. The range of variable aggregation levels estimated are not qualitatively incompatible with information for Australian orange roughy aggregations. Changing from the earlier to the updated beta distribution parameters increases medium term annual sustainable yield estimates for the resource as a whole from 1 850 to 4 400 tons, though the latter figure needs to be considered with caution as it is particularly dependent on the assumption that the beta distribution estimated for proportions aggregating at Frankies applies also to Johnies. Broadly speaking, MSY estimates at 1 600 to 3 500 tons are some 5–60% more than estimated a year previously. However, the varying proportions of abundance present at aggregations from year to year would lead to difficulties in making a catch of this size every year. DA - 2007 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2007 T1 - Age-structured production model assessments and projections including updated parameters to model the intermittent aggregation of Namibian orange roughy TI - Age-structured production model assessments and projections including updated parameters to model the intermittent aggregation of Namibian orange roughy UR - http://hdl.handle.net/11427/17986 ER - en_ZA


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