This dataset contains only the final cruise report on chum salmon survey in Strait of Juan de Fuca in autumn 2020. The project plan for 2020, the fifth year of the project, was very similar to previous years. Once approvals were obtained for clearance to fish in both US and Canadian waters, the vessel Nita Maria was chartered to fish based on a 4day per week schedule (2 days in Canadian waters and 2 days in US waters) for a 6 week period starting the 1st week of October 2020. Through the initial work on the ChumGEM reconstruction model, it was very apparent that the diversion of Chum salmon stocks through the southern route (Strait of Juan de Fuca) was a significant gap in our information needed to populate the model. Currently the model structure is available to incorporate this information but the assumptions on the migration pathways being used require investigation and validation.

The purpose of this project was to work towards addressing that data gap by sampling this migration route in both US and Canadian waters to determine:

• The spatial and temporal stock composition of Chum salmon migrating through the Southern Diversion route, • Provide sampling platform for stock identification, migration rate studies etc. • Develop time series of Catch per Unit effort data to pair with the Johnstone Strait Test Fishery to determine diversion rate of various Chum populations.

The program began as planned on September 29th and ran until November 6th. A total of 129 sets were completed (70 in Canadian waters and 59 in US waters). A total of 4,302 Chum were encountered and 1,794 were sampled for stock id and other biologicals. The Catch per Unit Effort (CPUE) was stronger in general on the Canadian side, similar to what was seen in 2017 and 2018. The catch information demonstrated a peak timing on the Canadian side of the Strait during week 43. Timing on the US side is problematic in 2020 as scheduling and weather issues during week 43 on the US side resulted in insufficient sampling. Over the period of the program, Chum CPUE was always higher in in Canadian waters than in US waters. Stock composition information demonstrated that Canadian Chum stocks dominated the samples throughout the Canadian waters similar to previous years. US Chum stocks in Canadian waters varied in composition but increased later in the program. In US waters, US Chum stocks dominated the mixtures throughout the program. Stock timing and distribution differences were observed and this new information has improved our understanding of Chum stock composition and timing through the migratory pathways of Juan de Fuca Strait.

Weekly target sample sizes were generally achieved in Canadian waters up until the last week of the program when Chum CPUEs dropped off. In US waters lower CPUE was encountered throughout the season and weekly sample targets were only achieved in weeks 41 and 42. It is hoped that with additional years of Chum CPUE data from this Southern approach (through Juan de Fuca) it will help to improve the existing relationship between Chum CPUE and abundance that exists for the Northern Approach (through Johnstone Strait).

This cruise is U.S. State Department MSR U2020-012 as part of the World Data Service for Oceanography. Report is in PDF.