Tagging studies indicate that the sardines which range from British Columbia in the summer, to southern California in the winter belong to the same stock: the northern population. The oldest age-groups of sardine in this stock migrate northward from California to B.C. in the summer, and complete a return migration in the fall. The migratory behaviour of sardine is complex and poorly understood. However, one generalization that emerges from historical and recent accounts is that sardines are particularly abundant off B.C. in warm summers when the northern population biomass exceeds 1 million tonnes. Both conditions appear necessary to produce a large run. Historically, an average of 10% of the northern stock appears to have migrated to B.C. The actual percentage varied from year-to-year in response to changes in water temperature, and other factors. The U.S. is currently harvesting the portion of the northern stock available to the California fishery at a rate of 5 to 15%. To be precautionary, the Canadian fishery should harvest the resource at similar rates, which would average about 10% of the biomass in Canadian waters. At current stock levels, and assuming a 10% migration rate the B.C. fishery could potentially harvest about 12,700 tonnes. However, for management reasons such as: 1) an undesirable bycatch of sensitive species like coho and chinook salmon or; 2) the appearance of sardines in sensitive (or unfishable) areas it may be advisable to set a lower quota for a few years, until the B.C. sardine fishermen become more experienced, and the bycatch risks associated with the fishery are more clearly understood. DFO must make it very clear to the industry from the outset that the allowable catch is a ceiling, not a target. Because of the dynamic and unpredictable movements of this highly migratory species there is no guarantee that the B.C. sardine fleet will catch the annual quota. Industry must also be aware that sardine undergo large fluctuations in abundance in response to variations in ocean climate. Accordingly, if the current favourable conditions begin to deteriorate the sardine could 'disappear' from the B.C. coast (for a while at least), like they did in the late 1940s. Regardless of whether a preseason or inseason biomass estimate is used to determine the total allowable catch, soundings should be conducted in inshore waters to assess the relative biomass of sardines in the area before a fishery commences. Even though sardine are highly migratory, all the catch should not be removed from one area. This requirement recognizes that sardine is a potential forage- fish in the ecosystem.
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