Research Document - 1999/165
Review of 1998 Terminal Run of Somass River Chinook Salmon, 1998 WCVI Extensive Escapement Indicators, and Somass Terminal Run Forecast for 1999.
By B. Riddell, W. Luedke, J. Till, and B. Patten
Abstract
The detailed assessments and forecasts of the Robertson Creek Hatchery/Stamp River (Somass) chinook are undertaken annually for management of ocean and inletterminal fisheries and as an indicator of the expected returns to the naturally spawning chinook populations along the west coast of Vancouver Island (WCVI). The following forecasts are based on returns through 1998, assumptions of ocean fishing mortality in Alaska and Canada, and using methods previously approved by PSARC.
The recommended forecast for total pre-fishery abundance of Somass/Stamp River chinook available in Canada is 76,000+20% based on averaging the Prod2 and Prod3 forecasts. This number includes both immature feeder chinook which will not mature in 1999 as well as chinook which will mature and be able to spawn in 1999.
Given internal Fishery Managers' recommendations on allocation to various fisheries, the recommended forecast forthe total terminal run of Robertson Creek Hatchery and Stamp River chinook (age 3,4, and 5) returning to Barkley Sound in 1999, is 39,000+20% based on averaging the Prod2 and Prod3 forecasts. The age structure of the return is projected to be: 13% Age 3, 11% Age 4, and 76% Age 5; with an expected sex ratio of 64% females. The number of chinook required to meet the minimum spawning escapement goal is 25,000. This goal is achievable if ocean fishing mortality is equal to or less than those assumed (footnote 1) and terminal catches do not exceed those allocated.
"Extensive" surveys of natural spawners in systems along the WCVI indicated improved chinook escapements in 1998, mainly due to strong returns from the 1994 brood. However, as with the Somass return, there was a seriously low number of age 3 chinook (1995 brood year) throughout the WCVI. This will result in low numbers of age 4 returns in 1999, which are usually the main age class in the run and the main age class in egg deposition.
In addition, indications of low age-2 male (jacks) jack returns in 1998 suggest a very low survival rate for the 1996 brood year (although note there can be large error in this estimate). However, two consecutive broods with poor survival could result in extreme conservation concerns in 2000. As a result, there is a continued need for conservative management plans in fisheries impacting these stocks during 1999.
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