Research Document - 1999/068
Review of 1997 terminal run of Somass River chinook salmon, and terminal run forecast for 1998.
By B. Riddell, W. Luedke and J. Till
Abstract
Based on returns through 1997 and using methods previously approved by PSARC, the recommended forecast for the total terminal run of Robertson Creek Hatchery and Stamp River chinook (age 3,4, and 5) to Barkley Sound in 1998 is 58,800+20% (based on averaging the Prod2 and Prod3 forecasts). The age structure of the return is projected to be 8% Age 3, 72% Age 4, and 20% Age 5; with an expected sex ratio of 52% females. The number of chinook required to meet the minimum escapement goal is 31,900.
The detailed assessments and forecasts of the RCH/Stamp chinook are undertaken annually for management of that major stock plus as an indicator of the expected returns to the naturally spawning chinook populations along the west coast of Vancouver Island (WCVI). Terminal run size and spawning escapements to the RCH/Stamp indicator stock have been similar over the past three years and are projected to be similar and relatively weak again in 1998. However, returns to some of the natural systems were better in 1997 than indicated by this stock. This is particularly true for returns to populations along the northern half of the Island (Areas 25 to 27); seven populations in these Areas are, in aggregate, used in the Pacific Salmon Commission (PSC) to indicate trends in escapement to naturally spawning chinook along the WCVI.
While this is positive indication that the conservation actions taken by Canada to protect these populations has been successful, there are two concerns which suggest caution when planning 1998 fisheries. First, the recovery in the northern population is not evident in the more southern naturally spawning populations (e.g., the Area 24 populations and Nahmint River). Secondly, the age structure of the 1997 returns was strongly age-4 chinook. Returns of Age-3 chinook to the natural systems did not appear as strong as the return to the RCH/Stamp indicator stock. Consequently, returns in 1998 may be reduced if survival of the 1994 brood year declined again. The only indication of brood survival for these northern populations is the return to Conuma Hatchery. Age-3 returns in 1997 to Conuma were only about 25% of the Age-4 returns observed in the sport fishery and in the escapement.
While the condition of most naturally-spawning chinook populations along the WCVI have improved during recent years, the above concerns and the relatively weak return forecasted for the RCH/Stamp stock indicate a continued need for conservative management plans in fisheries impacting these stocks during 1998.
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