Review of IOTC YFT & BET Assessment in 2019

Different approaches were examined for assessing YFT & BET in 2019. A large effort was made to address issues identified in 2018 and the analysts should be commended on that. With respect to YFT, assessment examined in 2019, substantial issues relating to data quality were examined. Various assessment methodologies were examined and concluded that the stock continued to remain overfished; this includes a continuity analysis from 2018; however few models did not indicate overfishing trajectories were present, but more time needs to be spent examining these models, and weighting issues across models, and the most appropriate use of tagging information Some diagnostics indicate that information content in indices and length composition is limited and fail under numerous hypothesis examined (runs test and hindcasting tests). However, a much more extensive section on diagnostics was presented in 2019 as compared to 2018. Issues on high-grading were dealt with appropriately, but spatial and piracy issues need further examination for the standardization of CPUE. Overall, the process was transparent, and issues were briefly discussed relevant to uncertainty in the assessment results.
For BET assessment, the model appears to be correctly specified with no issues of finding a global minima. Models examined had some issues with hyper-depletion hypothesis that were discounted as the weight of evidence is that there is a decline in biomass in Area 1. Model diagnostics were performed extensively, and there appear to be no serious retrospective patterns. There should be simpler models examined for BET to corroborate the base/reference sets of assessment. Data inputs with respect to tag weights should be examined, and an understanding of CPUE declines in Area 1 need to be addressed. Issues of catches for the PS fishery need to be addressed, as these have large implications on stock status for both YFT and BET species. Issues of dome-shaped selectivity and plausible effects were examined. These have large implications on the assessment. As with YFT, the process was transparent, and issues were briefly discussed relevant to uncertainty in the assessment results.
A key limitation was that insufficient time was available to examine both data and assessment issues on multiple species at the meeting. If we could discuss model resolution and data before the meeting by species, additional time would be available to discuss further refinements in the assessments.