Results for the Reference-case abalone spatial- and age-structured assessment model for Zones A, B, C and D in 2009
| dc.contributor.author | Brandão, Anabela | |
| dc.contributor.author | Butterworth, Doug S | |
| dc.date.accessioned | 2016-03-22T08:50:43Z | |
| dc.date.available | 2016-03-22T08:50:43Z | |
| dc.date.issued | 2009 | |
| dc.date.updated | 2016-03-22T08:49:17Z | |
| dc.description.abstract | A summary is presented of the results obtained from the Reference-case model described by Plagányi (2008) that was fit to Zones A, B, CNP, CP and D in combination (hereafter referred to as the “combined ABCD model”). The full details of the spatial- and agestructured production model (ASPM) are provided in Appendices 1 and 2. The Reference-case model (when the updated and extrapolated “old” CPUE series is used in the model fitting procedure) estimates a pristine spawning biomass, sp B0 (in tonnes) with 90% Hessian-based confidence intervals shown in brackets, of 9 876 (5 985; 13 767), 5 902 (5 449; 6 355), 7 462 (7 177; 7 747) and 10 439 (6 562; 14 316) for Zones A, B, C and D respectively. The 2010 (inshore+offshore) spawning biomasses (and associated 90% confidence intervals) of abalone in Zones A, B, C and D are estimated at ca. 29 % (23%; 35%), 26 % (19%; 32%), 6% (3%; 9%) and 11 % (8%; 14%) respectively of their preexploitation levels. The “nonpoached” CNP and “poached” CP areas of Zone C are estimated at ca. 11 % and 6 % respectively with the inshore region particularly depleted: the model predicts almost no remaining abalone in the inshore area of Zone D. Equivalent estimates for Zones A and B are 15% and 19%. The model estimate of the proportion poached from Zone A is 0.68 (90% Hessian-based confidence interval 0.58 – 0.77). Natural mortality is reasonably estimated (e.g. 0.32 yr-1 for age 0 and 0.13 yr-1 for age 15+) and in Zones C and D, the additional mortality estimated for 0-yr old abalone (due to the ecosystem-change effect) corresponds to near zero current annual survival rates. Poaching is severely impacting the resource, with Zone A particularly impacted in recent years. The combined Zones A-D model-predicted 2009 poaching estimate is 939 MT and corresponds to the assumption that, on average, 14% of all poached abalone are confiscated. | en_ZA |
| dc.identifier.apacitation | Brandão, A., & Butterworth, D. S. (2009). <i>Results for the Reference-case abalone spatial- and age-structured assessment model for Zones A, B, C and D in 2009</i> University of Cape Town ,Faculty of Science ,Marine Resource Assessment and Management Group. Retrieved from http://hdl.handle.net/11427/18143 | en_ZA |
| dc.identifier.chicagocitation | Brandão, Anabela, and Doug S Butterworth <i>Results for the Reference-case abalone spatial- and age-structured assessment model for Zones A, B, C and D in 2009.</i> University of Cape Town ,Faculty of Science ,Marine Resource Assessment and Management Group, 2009. http://hdl.handle.net/11427/18143 | en_ZA |
| dc.identifier.citation | Brandão, A., & Butterworth, D. S. (2009). Results for the Reference-case abalone spatial and age-structured assessment model for Zones A, B, C and in 2009. Marine and Coastal Management document: MCM. | en_ZA |
| dc.identifier.ris | TY - Working Paper AU - Brandão, Anabela AU - Butterworth, Doug S AB - A summary is presented of the results obtained from the Reference-case model described by Plagányi (2008) that was fit to Zones A, B, CNP, CP and D in combination (hereafter referred to as the “combined ABCD model”). The full details of the spatial- and agestructured production model (ASPM) are provided in Appendices 1 and 2. The Reference-case model (when the updated and extrapolated “old” CPUE series is used in the model fitting procedure) estimates a pristine spawning biomass, sp B0 (in tonnes) with 90% Hessian-based confidence intervals shown in brackets, of 9 876 (5 985; 13 767), 5 902 (5 449; 6 355), 7 462 (7 177; 7 747) and 10 439 (6 562; 14 316) for Zones A, B, C and D respectively. The 2010 (inshore+offshore) spawning biomasses (and associated 90% confidence intervals) of abalone in Zones A, B, C and D are estimated at ca. 29 % (23%; 35%), 26 % (19%; 32%), 6% (3%; 9%) and 11 % (8%; 14%) respectively of their preexploitation levels. The “nonpoached” CNP and “poached” CP areas of Zone C are estimated at ca. 11 % and 6 % respectively with the inshore region particularly depleted: the model predicts almost no remaining abalone in the inshore area of Zone D. Equivalent estimates for Zones A and B are 15% and 19%. The model estimate of the proportion poached from Zone A is 0.68 (90% Hessian-based confidence interval 0.58 – 0.77). Natural mortality is reasonably estimated (e.g. 0.32 yr-1 for age 0 and 0.13 yr-1 for age 15+) and in Zones C and D, the additional mortality estimated for 0-yr old abalone (due to the ecosystem-change effect) corresponds to near zero current annual survival rates. Poaching is severely impacting the resource, with Zone A particularly impacted in recent years. The combined Zones A-D model-predicted 2009 poaching estimate is 939 MT and corresponds to the assumption that, on average, 14% of all poached abalone are confiscated. DA - 2009 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2009 T1 - Results for the Reference-case abalone spatial- and age-structured assessment model for Zones A, B, C and D in 2009 TI - Results for the Reference-case abalone spatial- and age-structured assessment model for Zones A, B, C and D in 2009 UR - http://hdl.handle.net/11427/18143 ER - | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11427/18143 | |
| dc.identifier.vancouvercitation | Brandão A, Butterworth DS. Results for the Reference-case abalone spatial- and age-structured assessment model for Zones A, B, C and D in 2009. 2009 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/18143 | en_ZA |
| dc.language | eng | en_ZA |
| dc.publisher.department | Marine Resource Assessment and Management Group | en_ZA |
| dc.publisher.faculty | Faculty of Science | en_ZA |
| dc.publisher.institution | University of Cape Town | |
| dc.subject.other | Assessment model | |
| dc.subject.other | Spatial- and age-structured | |
| dc.title | Results for the Reference-case abalone spatial- and age-structured assessment model for Zones A, B, C and D in 2009 | en_ZA |
| dc.type | Working Paper | en_ZA |
| uct.type.filetype | Text | |
| uct.type.filetype | Image | |
| uct.type.publication | Research | en_ZA |
| uct.type.resource | Research paper | en_ZA |