JOINT CHINOOK TECHNICAL COMMITTEE
Joint Chinook Technical Committee. Preliminary Retrospective Analysis of the U.S. and Canadian Proposals for Abundance-Based Regimes for Chinook Fisheries. TCCHINOOK (99)-1. January 28, 1999.
In February of 1998, the United States (U.S.) and Canada exchanged proposals for abundance-based management regimes for chinook salmon. While many aspects of the proposals are similar, conceptual and technical differences exist. To identify and determine the significance of those differences, the Commissioners asked a bilateral workgroup to provide responses to a list of expository questions (see TCChinook (98)-01) and to conduct a retrospective analysis of the proposals. The retrospective analysis simulates the effects the proposed regimes would have had upon the fishing mortality, exploitation rates, and escapement of chinook salmon if the regimes had been in place from 1985 through 1996.
Briefly, both the U.S. and Canadian proposals include: 1) an abundance-based management approach for chinook salmon that includes limits for mixed-stock ocean fisheries (aggregate abundance-based management (AABM)) and constraints for the remaining fisheries (individual stock-based management (ISBM)); 2) provisions for adjusting allowable harvests in response to stock status; 3) a list of technical assignments; 4) approaches to reduce incidental mortalities; and 5) provisions for terminal exclusions, hatchery add-ons, and overage/underage policies.
The Chinook Technical Committee (CTC) has developed a version of the Pacific Salmon Commission (PSC) chinook model that provides the capability to simulate many features of the U.S. and Canadian proposals for AABM and ISBM regimes. Most importantly, the model now allows the specification of a set of rules that establish fishery specific impact limits that vary by year in response to the abundance of chinook salmon. The rules used by the CTC in this analysis are based upon our interpretation of the proposals (as assisted by the Commissioners during bilateral deliberations in December, 1998). However, not all features of the proposed regimes are currently simulated, nor are all factors affecting chinook salmon fishing mortality and escapement considered. Important limitations of the analysis include the following:
Survival Rates. The retrospective analysis does not address the question "What will be the effects of the proposed regimes on fishery catches and escapement in future years". Catch and escapement in the future will depend to a large extent on the effects of the freshwater and marine environment on chinook salmon survival rates. Survival rates for most stocks are currently substantially less than the rates for broods that were harvested in the late 1980s.
Stock Status. Provisions for adjusting fishery impacts in response to stock status are not simulated. This decision was driven by several factors: 1) the provision is not fully developed in the Canadian proposal; and 2) interpretation of the U.S. proposal is difficult, and implementation occurs "only for those stocks for which the escapement goal review has been completed and the escapement goal agreed to." The escapement goal review has not yet been completed by the CTC.
Fishery Impacts. Simulated fishery impacts are identical to the target catch or mortality in each year. In practice, uncertainty in predictions and management error will result in impacts that differ from the target values.
Time Stratification. The PSC chinook model does not currently have the capability to assess changes in stock composition, abundance, or exploitation rates at a time step finer than one year. Therefore, analysis of the Canadian proposal for the West Coast Vancouver Island (WCVI) and North of Leadbetter Point (NLP) troll fishery was predicated on the understanding that the total allowable mortalities would be computed based on the aggregate abundance of chinook available on an annual basis to the WCVI and NLP troll fisheries (see June 12, 1998 letter from the CTC to the chairs of the PSC).
Fishery Stratification. Fisheries in the PSC chinook model generally correspond to those identified in the U.S. and Canadian proposals. One exception is the NLP troll fishery referenced in the Canadian proposal. The closest approximation in the PSC chinook model, and the fishery used as a surrogate in the CTC analysis, is the U.S. south ocean troll fishery. This model fishery includes all troll fisheries off the coasts of the states of Washington, Oregon, and California that impact stocks from Puget Sound, the Washington Coast, the Columbia River, and far north migrating stocks from the Oregon coast (see June 12, 1998 letter from the CTC to the chairs of the PSC).