Description of a daily simulation model for the area 4 (Skeena) commercial gillnet fishery

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This report describes a daily simulation model for the Area 4 (Skeena River) commercial
gillnet fishery. The model evaluates the effects of various gillnet fishing patterns on the catch and escapement of sockeye, steelhead (including sub-stocks), early-run coho, chinook, and pink salmon migrating through four sub-areas of Area 4. For any fishing pattern, the model predicts the daily sockeye harvest rate associated with the fishing effort, and applies this rate to the abundance of salmon to calculate catch. The model uses sockeye harvest rate and effort relationships obtained from run-reconstructions of Area 4 fishery data for the years 1985 – 1991. The daily abundance of each species entering Area 4 depends upon the run sizes and run-timings used in the model. A return of 2.3 million fish to Area 4 is used as the expected sockeye run size. Run sizes for other species can be specified, or represented as proportions, for harvest rate calculations. The daily proportions of sockeye entering the fishery are derived from average reconstructed run-timing curves for the base-period years 1985 – 1991. The run-timings for other species are summarized from a combination of test fishery and tagging data, and are represented in the model as normal distributions. The model is spreadsheet based, and evaluates any combination of fish abundance and gillnet fishing pattern, including the use of gillnet weedlines and catch and release for steelhead. Changes in harvest rate are measured about the pattern for the 1985 – 1991 period.