Note: the core data sets referenced in this report are available here.
Note: this analysis has since been extended to include estimates of escapement and exploitation rates back to the 1950’s. The results of the extended analysis are available here.
A large amount of time and resources are expended each year by DFO, PSC, First Nations, stewardship groups and NGOs to obtain the catch and escapement data needed to monitor trends for BC salmon stocks and Conservation Units (CUs). Some of these data are combined in regional or coast-wide models to derive estimates of run size and exploitation rates for specific salmon indicator stocks (e.g. Northern Boundary Sockeye model; PSC Chinook and NCCC Coho models). In most instances, the results from these substantial data collection and analysis efforts have not been fully applied to the challenge of tracking trends in catch and escapement by CU.
LGL Limited was contracted by the Pacific Salmon Foundation in October 2011 to work with DFO stock assessment biologists to update the core datasets, database systems and analysis tools needed to track stock status and trends for BC salmon stocks. This project builds on a previous work supported by the State of the Salmon Program (SOS) in 2008-09 to produce estimates of escapement, catch and run size for each BC Salmon CU (English et al. 2009).
The analytical procedures used to compute escapement, catch and run size estimates for each SA and CU range from the relatively simple summation of annual catch and escapement estimates to complex run reconstruction techniques. The foundation for the escapement estimates presented in this report is the nuSEDS database and list of indicator streams identified by NCCC biologist as the most reliable set of escapement data available for each CU. All of our analyses are linked directly to a downloaded copy of the nuSEDS database so these analyses can be readily updated as new information is loaded into the database. The critical step in the escapement estimation process was identifying the streams with the most reliable escapement records. The DFO regional biologists identified 781 stream-species combinations where escapement survey data was of sufficient quality and quantity to be used as an indicator of annual escapement trends for a specific CU (Table 7). The majority of these indicator streams (81%) were assigned survey quality ratings of fair (2) or good (3). The streams with the highest quality survey data (ratings of 4 and 5) accounted for 6% of the indicator streams and 13% of the indicator streams were assigned a poor quality rating. This report provides details on the methods used to convert the escapement estimates for indicator stream into total escapement estimates for each Statistical Area and CU as well as a description of the sources of the exploitation rate estimates need to compute annual harvest and total run size estimates for each salmon CU. The last section of the report provides several recommendations regarding improvements to DFO databases and further analyses that should be conducted to assess the sensitivity of CU specific exploitations rates to different assumptions regarding run timing through coastal fisheries.