Trends in the Abundance of the Ocean Stage of River and Pacific Lampreys

Pacific lamprey and river lamprey are caught incidentally in trawls used to catch juvenile Pacific salmon in the Strait of Georgia. Both species could escape through the meshes in most of the net except for the small mesh at the cod end. Thus, we propose that the catches of lamprey probably are a relative index of abundance among years. From 1998 to about 2004, river lamprey abundances remained relatively stable and then declined by about 60% from 2005 to 2011. Because the ammocoetes of the river lamprey dominate the benthos of the lower Fraser River, the decline in catch is believed to be related to reduced abundance of mainly Pacific herring and juvenile Pacific salmon. Catches of Pacific lamprey declined more gradually over the same period, reaching the lowest levels from 2003 to 2008. Since 2008, catches have increased, with some record catches in sets in 2013. There are approximately 87 rivers that empty into the Strait of Georgia and Pacific lamprey probably occur in all these rivers. Thus, the decline in abundance in the mid-2000s probably is related to reduced prey which is consistent with a known period of generally poor fish production.