Salish Sea Marine Survival Project

71 Table 2. Comparison of freshwater survival of juvenile Chinook down Cowichan River: comparing different release locations and timing (early versus late releases). RELEASE LOCATION (River km) RELEASE DATE HATCHERY CWT RELEASE NO. POPULATION ESTIMATE AT RST IN LOWER RIVER % SURVIVAL Stoltz (25.7) 27 April 94,530 29,465 31.20% Road Pool (46.5) 9 May 94,034 10,093 10.70% Horseshoe Bend (31.7) 24 May 194,315 91,815 47.30% Road Pool (46.5) 20 June 193,748 29,422 15.20% Total 576,627 160,796 27.90% 2. Impacts of Release Locations: Cowichan River Chinook Hatchery Salmon Projects The Cowichan River Chinook population was historically one of the larger Chinook stocks in the Salish Sea. PSF has supported several studies relating to Cowichan River Chinook, including studies of relative survivals of both hatchery and wild fish in both freshwater and marine environments. Rotary screw trap (RST ) studies conducted during the downstream migration of hatchery smolts, which in 2015 and 2016 were released 40 kms upstream of the mouth of Cowichan River (i.e., at Road Pool), found that only 20% of the releases could be accounted for in the RST located in the lower river. Based on the 2015 findings, DFO and Cowichan hatchery also agreed to carry out paired release trials of CWT Chinook during 2016, one at the upper river and one at the lower river. Coded wire tags (CWTs) were applied to 4 release groups of Cowichan hatchery Chinook. These fish were released on two dates in April and two dates in May to make for 2 early and 2 late Cowichan Chinook releases in-river. Both early and late groups also were released at two different locations: the Road Pool (40 kms upstream and labelled the standard release site on Figure 2) and approx. 20 kms downstream. The smolts were supplemented with river water 2-3 hours per day, 2-3 times per week for a month period before release to assist with imprinting. The survival estimates were lower for the upstream releases (Road Pool) versus the downstream releases for both the early and later releases (see Table 2 below). It was recommended that the lower release sites be used in all future Cowichan Hatchery release plans. Further PIT tag and in-river predator studies carried out in the Cowichan River during SSMSP have suggested that the freshwater losses may be a result of predation from herons and other predators, exacerbated when there are low flows in the river; this may be a result of heron predators which 0 km 5 km 10 km ROAD POOL BELOW WEIR Lake Cowichan Cowichan Bay ABOVE WEIR Skutz Falls RIVERBOTTOM ROAD RST Locations Hatchery Release Site ART WATSON'S BLOCK 51 COWICHAN RIVER PUMPHOUSE DUNCAN FORKS COWICHAN HATCHERY Quamichan Lake Figure 1. Rotary screw trap used to catch juvenile Chinook on Cowichan River Figure 2. Release sites for Cowichan Hatchery Experimental Releases like to forage in shallow waters less than 15cm deep (see Freshwater Studies summary). An interesting observation was that 75% of the smolts taken by herons were found to be hatchery fish, indicating possibly different behaviour or predator responses by these Chinook. Based on these findings it was suggested that high hatchery losses could be reduced by simply moving the point of hatchery release, a finding that has resulted in a change in hatchery practices: Chinook from the Cowichan hatchery are no longer released in the Cowichan headwa- ters, but instead, are released in the lower river or directly from the hatchery.

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