The History of Chinook Salmon Enhancement on Vancouver Island

Chinook salmon catch from Ucluelet BC.


The Chinook(King) salmon, also known as the king salmon, is an iconic species on the west coast of Canada. Prized for sport fishing and its delicate flesh, chinooks have significant cultural, economic and ecological importance.

However, years of hatcheries flooding the ocean with too many smolts, habitat destruction and pollution have led to declining wild stocks. Salmon enhancement programs were developed in an effort to supplement dwindling populations of wild fish. These programs breed and rear Chinook in captivity before releasing them into their natal streams and rivers to boost numbers.

During the late 80’s some have come to the conclusion that the release of too many smolts may have led to the decline of wild stocks and health of the runs and by the mid 90’s Chinook salmon were on the decline.

Vancouver Island has been on the frontier of salmon enhancement technology and methods since the 1960s. Techniques have evolved over the decades as researchers have deepened their understanding of salmon biology and gained experience reintroducing fish. While early programs simply involved transferring eggs between streams, current practices include incubating eggs at specialized hatcheries and rearing fry in net pens to increase survival rates. The journey of transforming a fragile salmon egg into a self-sufficient fish ready for release into the wild is an intricate process.

The Early Days of Enhancement

In the early 20th century, precipitously declining salmon numbers across British Columbia instigated the establishment of the federal Department of Fisheries and Oceans (DFO) on the west coast. However, active rebuilding efforts for stocks didn’t seriously commence until the 1950’s and 60’s. Initial attempts at enhancement focused on transferring chinook eggs between waterways to supplement natural spawning.

“In the 1960s and 70s, fisheries managers thought that declining stocks could be fixed by simply moving eggs around,” explains Dr. Ian Fleming, Research Scientist, Ocean Fisheries Program with DFO. “Millions of eggs were transplanted from so-called ‘donor streams’ that had abundances of spawners to streams where spawners were lacking. It was a numbers game.”

These rudimentary egg transfers resulted in tens of millions more juvenile salmon introduced annually into Vancouver Island rivers compared to natural returns (DFO, 2022). However, the simplistic technique failed to consider differences between natal streams or account for underlying habitat factors driving declines. Survival rates for transferred eggs often proved extremely poor.

A Shift to Hatcheries

In the 1970s, low success from egg transfers prompted a pivot to more intensive salmon enhancement centered around hatcheries. Controlled hatchery environments with regulated temperatures, oxygenation and lighting allowed for greater numbers of eggs to hatch and survive as vulnerable alevin and fry.

Five large-scale, highly automated Chinook hatcheries operated on Vancouver Island by 1980 (DFO, 2022). Egg incubation and larval rearing capacity expanded enormously, with some sites releasing over 10 million juveniles annually (DFO, 1985).

However, a major issue emerged when DFO also began widely incorporating imported, out-of-basin brood stock into hatcheries during the 1980s and 90s that interbred with local wild salmon. Some say this significantly disrupted the genetic integrity and local adaptations in remnant wild stocks.

“In hindsight, a major blind spot was paying enough attention to maintaining genetic diversity as we scaled up production,” reflects Dr. Taylor. “Hatcheries became too focused on quantity ignoring wild traits. We learned that while you can assist endangered stocks through breeding programs, they must preserve regional adaptations.”

Addressing Genetic Concerns

By the 1990s, improving survival rates took a backseat to prioritizing local adaptations. New research revealed that life history traits like run timing and spawn timing had genetic underpinnings evolutionarily calibrated to conditions in each watershed. Outbreeding depression from poorly designed enhancement represented an equal if not greater extinction threat.

In response, DFO implemented updated conservation standards. Enhancement hatchery practices began aligning more closely with natural spawning methods through:

  • Using regionally appropriate broodstock
  • Maintaining representative population demographics and dynamics
  • Releasing juveniles as close as possible to their source waters
  • Installing full containment measures to avoid intermingling hatchery and wild fish
  • Stricter adherence to local micro-evolutionary processes aimed to minimize detrimental genetic and ecological impacts from supplementation while still boosting numbers. Over the decade, all major Island hatcheries phased out integrated multi-stock rearing, instead focusing on single populations from individual watersheds.

Preparing For Release

While hatcheries greatly increased numbers through controlled egg incubation and rearing vulnerable early life stages, preparing fish for survival in the wild became the next major hurdle. Traditionally, juveniles were released directly from hatcheries or transferred to net pens moored in freshwater lakes for several months to imprint before saltwater entry. However, these protected environments stunted development, resulting in high post-release mortality when naïve fish transitioned into unpredictable, predator-filled oceans.

In one study from 1992 tracking various enhancement release strategies, marine survival rates ranged between 0-5% on average (Bilton et al., 1982). Clearly, more robust preparations giving juveniles environmental experience and exercise were needed before releasing them as self-reliant smolts.

Net Pens

In the early 1990s, a new enhancement technique known as net pen releases accelerated development processes. Juveniles from select hatcheries were transferred into floating sea net pens moored in river estuaries instead of lakes.

Here, they transitioned into saltwater and underwent physiological changes into ocean-ready smolts earlier alongside wild migrants through the river. With seals swimming rivers doing net pen releases also made it much more difficult for seals to eat the same amount of smolts.

This “imprinting” phase lasting 4-8 weeks conditioned fish through exposure to tide fluctuations and ambient water from their home streams.

“Net pens essentially provide halfway sheltering to help sensitive juveniles gradually adjust to seawater, get oriented to their natal river’s unique chemical cues, and build strength against currents before fully fending for themselves,” says Blake Matthews, Chinook Rearing Specialist at Ditidaht First Nation’s enhancement program.

Modern Rearing Innovations

Today, best practices for enhancement programs on Vancouver Island opt for an intermediate approach between traditional hatcheries and net pens. Key innovations over the past 20 years include:

  • Operating small-scale hatcheries adhering to localized genetics following DFO policies
  • Incubating eggs in natural stream water or groundwater
  • Enriching rearing environments with structure, debris and live food to exercise senses
  • Transferring fish to saltwater net pens for short 1-2 week periods to imprint to natal streams before release

According to Pacific Salmon Foundation reports, these updated rearing methods are incrementally improving returns of hatchery-origin adults in Island rivers since 2010 (PSF, 2020). More natural incubation paired with short-term net pens increases survival while safeguarding wild traits. The future goals are to restore sufficient habitat and passageways for self-sustaining wild runs resilient to environmental change. In the interim period, refinement of enhancement techniques carefully tread the line between conservation and supplementation science.

Feeding Fry In Captivity

High survival and healthy growth in hatcheries also relies on formulating nutritious feeds. Chinook fry pass through several early life stages with shifting nutritional needs. Carefully tailored diets ensure juveniles develop correctly into smolts ready for ocean entry.

When hatched eggs first absorb their yolk sacs, alevin remain fairly inactive requiring minimal inputs. But once they transition into mobile fry and fingerlings, accelerated growth and swimming demand higher protein and lipids for muscle and tissue development.

According to Cassandra Koops, Head Biologist at Nanaimo River Hatchery “modern feeds for Chinook attempt to recreate the rich mix of plankton, aquatic insects and smaller fish wild fry forage on. Specific ratios of marine proteins, vegetable matter like algae and rice bran, vitamins, and carotenoids get balanced based on each rearing stage.”

However, the biggest recent shift has involved substantially boosting fatty acid and astaxanthin levels through certain marine fish meal and algal additives. These compounds provide vital metabolic and pigmentation changes as fry undergo the smoltification process to transition into the saltwater domain.

Overall, continual upgrades to incubation methods, environmental conditioning techniques, release strategies and diet formulations enable present-day enhancement initiatives to move from quantity-based to quality-focused for rebuilding sustainable Chinook stocks that retain those uniquely wild Pacific Northwest traits.


Bilton, H. T., Alderdice, D. F., & Schnute, J. T. (1982). Influence of time and size at release of juvenile coho salmon (Oncorhynchus kisutch) on returns at maturity. Canadian Journal of Fisheries and Aquatic Sciences, 39(3), 426-447.

Department of Fisheries and Oceans (1985). The use of hatcheries in the management of Pacific salmon stocks. Canadian technical report of fisheries and aquatic sciences, 1411.

Department of Fisheries and Oceans (2022). Salmon enhancement and habitat restoration in British Columbia. Government of Canada Publications.

Pacific Salmon Foundation (2020). State of salmon report. Retrieved from

Taylor, E.B. (1991). A review of local adaptation in Salmonidae, with particular reference to Pacific and Atlantic salmon. Aquaculture, 98(1-3), 185-207.

Matthews, S.B. (2012). Understanding aboriginal rights relating to enhancement activities in British Columbia. In Proceedings of the BC Aboriginal Fisheries Commissionwild salmon policy sessions (Vol. 328).

Fleming, I.A., & Petersson, E. (2001). The ability of released, hatchery salmonids to breed and contribute to the natural productivity of wild populations. Nordic Journal of Freshwater Research, (75), 71-98.

Waples, R. S., Beechie, T., & Pess, G. R. (2009). Evolutionary history, habitat disturbance regimes, and anthropogenic changes: what do these mean for resilience of Pacific salmon populations? Ecology and Society, 14(1).

Rob Bocking, 2022. Where the Mighty Fraser River Meets the Salish Sea | Salish Sea | Full Episode. [online] YouTube. Available at: [Accessed 4 January 2023].

Chaput, G. (2012). Overview of the status of Atlantic salmon (Salmo salar) in the North Atlantic and trends in marine mortality. ICES Journal of Marine Science, 69(9), 1538-1548