Research Document - 2004/005

Stock Assessment for British Columbia Herring in 2003 and Forecasts of the Potential Catch in 2004

By Schweigert, J.

Abstract

Herring stock abundance in British Columbia waters was assessed for 2003 and forecasts were made for 2004 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 2002 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. In addition, a year specific logistic function was introduced to model the availability of fish on the spawning grounds. In addition, the effect of a range of penalty weights on a series of indicators was investigated and the penalty weight was increased on the spawn data and decreased on the catch-age data for the final assessment. The effect on overall biomass levels was minimal except for the Queen Charlotte Islands where it resulted in a slight decrease in abundance over the time series. 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. However, a number of samples from the Strait of Georgia were not aged due to resource limitations. All available data were included in and summarized from an Access database. Coastwide, the estimated pre-fishery stock biomass for all assessment regions in 2003 was 246,000 tonnes based on the age-structured model which represents a 28% 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 three northern stocks also increased slightly as a result of a good recruiting 2000 year-class.

Complete document (PDF, 1309 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.