The number of adult wild steelhead trout returning to the Keogh River on northern Vancouver Island between December 2009 and the end of April 2010 was estimated by mark-recapture methods. The summed mark-recapture estimates of males and female spawner abundance was 54 wild spawners (95% CL of 14 to 54), of which 25 were females. These were supplemented by an estimated 57 (95% CL of 9 to 118) hatchery strays, giving a total of 111 potential spawners. A Logie 2100C resistivity counter and adjacent trap near the river mouth provided an independent estimate of 127 fish entering the river. These low adult spawner numbers were due to the continued low rate of survival from smolt to maiden-run adult. Smolts that emigrated in 2007 returned at a rate of 3.1% for wild fish, while returns of maiden-run adults (1-ocean and 2-ocean adults) from the 2008 smolt emigration were 1.9% to date. These were extremely low rates of survival compared with the 30-yr record (geometric means: overall 7.4%; 1977-1989, 14.2%; 1990-2007, 4.7%). One of the 7 wild adult returns sampled prior to spawning was a repeat spawner, based on scale analysis. The steelhead smolt yield (1 887 fish) enumerated at the rivermouth counting weir during spring 2010 was low, given the potential contribution from Living Gene Bank (LGB) spawners in the 2007 brood year (70 females). This yield represents approximately 28% of the estimated smolt rearing capacity for Keogh steelhead (~6 750 smolts) prior to the change in marine survival regimes and subsequent instream restoration efforts. The assignment of the 2010 smolts to their brood years based on the scale-determined ages of a size-stratified subsample resulted in an estimate of 24.7 smolts per female spawner from the 2006 spawners if it is assumed that only wild fish contributed to smolt production. However, if LGB spawners from the 2006 brood year were included in these calculations, the yield estimate fell to 8.3 smolts per female, similar to that expected
McCubbing, D.J.F., Lloyd Burroughs and N.T. Johnston. 2011. Adult steelhead trout (Oncorhynchus mykiss) and salmonid smolt migration at the Keogh River, B.C., during winter 2009 and spring 2010.. Ministry of Evironment. Fisheries Project Report. 134
Topic: Fish and Fish Habitats
Keywords: Steelhead Trount, Keogh River,
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