Browsing by Subject "ASPM"

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    A Bayesian assessment of the South Atlantic population of albacore which explicitly models changes in targeting
    (International Commission for the Conservation of Atlantic Tuna (ICCAT) Secretariat, 2004) Rademeyer, Rebecca A; Butterworth, Doug S; Penney, Andrew J
    The primary assessment method applied to South Atlantic albacore during the October 2000 ICCAT SCRS assessment session was an age-structured production model which assumed a fleet-aggregated selectivity pattern with a single change only (in 1969), and estimated model parameters using only CPUE data. A particular problem of this approach is that the Japan CPUE series is not considered comparable over the complete period for which it is available because of changed targeting practices, so that this series needs to be split into three separate segments when estimating model parameters. This paper refines that 2000 assessment by treating the Japanese, Taiwanese and Brazilian fisheries all as initially primarily albacore directed fisheries which have shifted over time to bigeye tuna targeted fisheries, taking albacore as a decreasing bycatch. The transitions over time are explicitly estimated, as are separate selectivities for the two components of each national fishery by also including catch-at-age information in the data fitted by the model. Compared to the high levels of uncertainty in past assessments, the refined model provides a reasonable to good fit to all available information, and suggests that the productivity of the resource is somewhat higher than estimated previously.
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    Report on an investigation of reasons for differences between outputs from ASPM and ADAPT-VPA assessments of the Gulf of Maine cod stock
    (2005) Butterworth, Doug S; Rademeyer, Rebecca A; Plagányi, Éva E
    The application of ADAPT-VPA and ASPM assessment methods to the same data set for the Gulf of Maine cod stock allows two primary reasons for earlier differences in assessment results from these two approaches to be identified: • the longer period of data which the ASPM method is able to take into account; and • decreasing selectivity at larger ages estimated by the ASPM approach, in contrast to the flat selectivity assumed by the ADAPT-VPA application of Mayo et al. (2002). Arguments are presented that the ASPM approach (with specific details of an application still to be discussed) should be preferred over ADAPT-VPA as the basis for management recommendations for this resource. Since the ASPM assessments consistently indicate the resource status to be appreciably better relative to the MSY biomass, this has important implications for what might constitute appropriate management measures at present.