Research Document - 2001/140

Stock Assessment for British Columbia Herring in 2001 and Forecasts for the Potential Catch in 2002

By Schweigert, J.

Abstract

Herring stock abundance in British Columbia waters was assessed for 2001 and forecasts were made for 2002 using two analytical methods: (1) escapement model; and (2) age-structured model. These models have been applied to assess herring abundance since 1984 but for the current assessment a number of changes were introduced in the age-structured model to account for temporal change in the spawn index. This revised age-structured model incorporates a fixed spawn conversion factor for the dive survey era since 1988 and a free fitted parameter for the earlier surface survey period. The revised age-structured model was adopted as the basis for the assessment of abundance in all five stock areas. All available biological data on total harvest, spawn deposition, and age and size composition of the spawning runs were used to determine current abundance levels. No significant problems were evident in the extent and comprehensiveness of the data collections. Coastwide, the estimated pre-fishery stock biomass for all assessment regions in 2001 was 211,000 tonnes based on the revised age-structured model. This represents a 14% increase over the 2000 abundance level. This slight increase reflects the recruitment of an average 1998 year-class in most areas of the coast except the Central where recruitment was poor.

The estimated harvestable surplus in 2002 (20% of the 2002 forecast herring run) based on forecast abundance to the five assessment regions is 38,950 tonnes for the B.C. coast assuming average recruitment to all areas. However, since consensus on stock levels for each assessment region may change as a result of PSARC review of these data, forecast run sizes, and harvestable surpluses, are subject to change.

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