At this meeting, the SSC and the Council reviewed a new ADF&G model for assessing the postseason abundance estimates for Chinook salmon on the Kuskokwim River, which is a contributing factor in the specification of the Chinook salmon PSC limit for the Bering Sea pollock fishery each fall.
Amendment 110, implemented in July 2016, modified the Chinook and chum salmon bycatch avoidance program in the Bering Sea pollock fishery. In addition to other measures, this amendment identified additional management actions that would be taken when a three-river index of Western Alaska inriver run abundance (Unalakleet River, Upper Yukon River, and Kuskokwim River) falls below a 250,000 Chinook salmon threshold, based on the State of Alaska’s post-season inriver Chinook salmon run size assessment.
Since 2015, ADF&G has generated postseason abundance estimates for the three rivers that comprise the index using methods consistent with the analysis for Amendment 110. This year, ADF&G has recommended changes to the data and model used to estimate total inriver abundance of Kuskokwim River Chinook salmon. The changes to the Kuskokwim River run reconstruction model were developed, in part, to address changing harvest patterns that resulted when significant harvest restrictions were implemented. Between 2014 and 2017, annual Chinook salmon harvest in the Kuskokwim River was among the lowest on record in this river. The previous model overestimated the total Chinook salmon runs in those years. For purposes of use in the 3-river index, ADF&G has indicated that any modification to the methodology for estimating these post season abundance estimates would be reviewed in the Council process before being adopted for the index.
The SSC and Council reviewed this new model for assessing the Kuskokwim River by the ADF&G. The SSC appreciated the time and effort that has gone in to model improvements and indicated that it represents an improvement over the previous model. The model is scheduled to be used both for in-river management in 2018 as well as for contribution to the 3-river index for federal management of the Chinook salmon bycatch limit for 2019 specifications. A companion document was provided for understanding the implications of the model revisions on the relationship of the three-river index to western Alaskan AEQ, which was the basis for the 250,000 fish threshold that was set in Amendment 110. The new scaling of the model using more recent mark recapture data results in much lower estimates of the total run than the previous model. New estimates of the adult equivalency (AEQ) for Coastal West Alaska (CWAK) genetic stock grouping were compared against those available when the Council took final action on Amendment 110 to establish the 3 River index as well as with the updated model used to assess the Kuskokwim contribution to the 3 River index. When this index is below the threshold, it results in lower PSC cap (45,000) and performance standard (33,371) for the pollock fishery for the following fishing year. The determination for 2019 will be made in October during the Council’s action to establish proposed specifications for groundfish. The Council had extensive discussion of the utility of a knife-edge threshold such as status quo as compared to a more dynamic biological reference point for determination of low Chinook abundance resulting in the move to a lower cap level. The Council will continue to consider whether to revisit this threshold analysis in the future, but took no action to do so at this time. Modification of the threshold requires an FMP amendment. Staff contact is Diana Stram.