Research Document - 2005/083
An assessment framework for Pacific herring (Clupea pallasi) in British Columbia
By Schweigert, J.F.
Herring stock abundance in British Columbia waters is assessed 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. Accurate estimates of current and future stock abundance rely heavily on consistent and reliable biological sampling of the populations. Extensive SCUBA surveys are conducted throughout the British Columbia coast to enumerate the numbers of fish spawning in each area and this information forms an important part of the data for determining total abundance in the age-structured model. Additional data on total harvest, fish size and age structure of the spawning runs are used to determine current abundance levels. As in recent assessments a fixed spawn conversion or catchability factor is applied for the dive survey era beginning in 1988 and a free fitted parameter is estimated for the earlier surface survey period. In addition, a year specific logistic function is applied to model the availability of fish on the spawning grounds. Forecasts of future stock abundance are developed from estimates of historical recruitment and used to provide advice on allowable harvest. The harvesting policy permits a maximum of up to 20% removal of the forecast spawning biomass provided the abundance is greater than the fishing threshold or Cutoff level established to conserve biomass in periods of reduced productivity.
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