Research Document - 2002/110

Stock Assessment for British Columbia Herring in 2002 and Forecasts of the Potential Catch in 2003

By J. Schweigert

Abstract

Herring stock abundance in British Columbia waters was assessed for 2002 and forecasts were made for 2003 using an age structured assessment model for the major stock assessment regions and an escapement model for the minor stocks in Areas 2W and 27. These models have been applied to assess herring abundance since 1984. As in the 2001 assessment, changes to the analytical model were introduced to account for temporal change in the spawn index. A fixed spawn conversion or catchability factor was applied for the dive survey era beginning in 1988 and a free fitted parameter was estimated for the earlier surface survey period. 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. All data were included in and summarized from an Access database which differ slightly from earlier procedures. Impacts on estimated run size was shown to be minor. Coastwide, the estimated pre-fishery stock biomass for all assessment regions in 2002 was 233,000 tonnes based on the age-structured model which represents a 21% increase over the 2002 abundance level. This increase reflects increased abundance in the south coast stocks particularly the Strait of Georgia. However, abundance in the Queen Charlotte Islands is depressed and fisheries should be closed for conservation considerations.

The estimated harvestable surplus in 2003 (20% of the 2002 forecast herring run) based on forecast abundance to the five assessment regions is 41,530 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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