Strait of Georgia Coho Hatchery Release Studies
SEP and PSF have been working in partnership on several projects designed to assess hatchery-wild salmon interactions in the Salish Sea, as well as to improve understanding of the behaviour, marine distribution, habitat use and competition between hatchery and wild salmon. This work also investigates various means to produce hatchery fish that survive at higher rates in the marine environment, which could then allow for reductions in hatchery production while sustaining or improving adult salmon production.
Delayed release of hatchery coho and Chinook salmon
This study has two main objectives of exploring release strategies that may improve the marine survival rates and distribution of hatchery coho and Chinook salmon, as well as reducing competition in the early marine environment between hatchery and wild salmon. Five hatcheries (Big Qualicum, Quinsam, Seymour, Inch and Chilliwack) will hold trial groups of Chinook and/or coho salmon in the hatchery beyond the traditional release timing of May through to late June/early July, which is several weeks after most wild juveniles, will have entered the marine environment. Juvenile fish will be released at a size that is expected to be consistent with naturally occurring salmon in the ocean at that time. By holding hatchery salmon longer, a period of several weeks of potential competitive interactions is eliminated. In addition, both recent (Beamish) and historic (Bilton) scientific work has suggested that juvenile salmon that enter the Strait of Georgia later and larger and that are able to grow fast are able to survive at higher rates than those that enter earlier. Furthermore, studies on wild coho at Black Creek have demonstrated that wild coho that enter the marine environment later and larger can have a tendency to maintain an “inside” distribution with the Salish Sea. For hatchery coho, this means that they would be more susceptible to catch in the summer Georgia Strait sport fishery, which historically was as high as 1 million fish retained.
Funding from the PSF supports the costs associated with extended rearing and coded wire tagging of these experimental releases. This study is being conducted at multiple locations around the Strait of Georgia over a period of several years. During 2016, costs are for CWTs for an experimental late large release of Seymour River coho, and for food costs for delayed release cohorts of coho and Chinook at Quinsam and Big Q hatcheries. 100K chinook smolts from 2015 Brood at Quinsam and 60K at BQ Hatchery were coded wire tagged, reared starting in Jan-Feb 2016 and released in early June at Quinsam and in July 2016 at BQ River.
DFO will be responsible for the monitoring and analyses of marine exploitation and escapement to determine overall survival compared to standard production releases in May (i.e. Brood return years 2016 to 2020 will be analysed; most adult returns are 3 and 4 year olds). The table below shows the delayed chinook and coho releases at Quinsam and BQ during 2016:
Cowichan River Chinook Salmon Coded Wire Tag Application
The Cowichan River Chinook population was historically one of the larger Chinook stocks in the Salish Sea. This hatchery stock is a Pacific Salmon Treaty indicator stock, which is used to provide information that is critical to the management of wild Chinook salmon in Lower Georgia Strait. The PSF has been supporting several initiatives relating to Cowichan River Chinook studies, including genetic-based hatchery-wild interaction work.
Rotary screw trap (RST) assessments conducted on the migration survival of hatchery smolts which were released 40 kms upstream of the mouth of Cowichan River in 2015 and 2016 (ie. Road Pool) found that only 20% of the releases could be accounted for in the RST located in the lower river. Based on these findings, DFO and Cowichan hatchery agreed to carry out paired release trials of CWT Chinook during 2016, one at the upper river and one at the lower river.
During 2016, 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. (Early and late groups were released at the Road Pool and approx. 20 kms downstream). In addition, approximately 140K CWT hatchery smolts were also released directly from Cowichan Hatchery May 24th to determine if overall adult survival improves compared to smolts released 40 and 20 kms upstream. 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 individual survival estimates for the upstream (Road Pool) versus downstream releases were 13.7% and 42.0%, respectively. It is recommended that the lower release sites be used in all future Cowichan Hatchery release plans.
To maximize the information content from these studies, the Science Panel strongly recommends a collaborative program with the Department of Fisheries and Oceans to reduce the numbers of smolts released into the Strait of Georgia. Since the 2009 program development though, significant reductions in smolts released have been undertaken, from 6.75M in 2009 to a planned release of just over 4M in 2016 ( ~40 % reduction). Further reductions for the SSMSP are not anticipated.