Hatchery-Wild Interactions

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.


This project has successfully collected broodstock for experimental releases of Chinook and Coho salmon at 2 hatcheries on the East Coast of Vancouver Island (Quinsam and Big Qualicum) for three years (2014-2016). The SSMSP has funded the extended rearing and feeding of late and larger Chinook and Coho at both hatcheries.  In addition to the work at Big Qualicum and Quinsam, the SSMSP has funded the coded wire tagging of a late large release of coho at the Seymour River in Burrard Inlet. Outside of the SSMSP-funded activities, SEP is also conducting a late large coho trial at Chilliwack and Inch Creek hatcheries, which began in 2014 and 2013 respectively.

In each brood year, a group of 100K salmon from each stock have been reared and released at a later date than the traditional production group, typically ~ June 21. These Chinook & Coho have been released at a larger size than the traditional May releases, however their growth is intended to mimic what would be expected in the marine environment had they been release in May. This project is based on work by Beamish (pers. Comm.) and Bilton (1978) that indicated that a later sea entry and larger body size may promote an increased marine survival for Chinook and coho. A secondary hypothesis was that a later and larger coho smolt may remain in the Strait of Georgia at a higher rate in its second summer at sea, which was observed in the 1980s and early 1990s when survivals were higher and coho were available to sport catch on the inside.

To date, data collection and results have been limited the first brood year 2013 and 2014 coho releases. Uncertainty has not yet been calculated, but the preliminary results appear to be mixed. The mainland populations (Inch, Chilliwack and Seymour) do not appear to benefit from a late large release while the Vancouver Island populations (Quinsam and Qualicum) showed promising results in the 2017 return.   Complete brood year cohort results from subsequent years will provide clarity on the utility of this strategy as a means to increase marine survival of hatchery coho and Chinook salmon.  Chinook salmon trial results will not be available until 2019 at the earliest.

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.