Sapporo Wild Salmon Project: Wishing Salmon to Live Naturally even in the City

The Toyohira River was once famous for its “Comeback Salmon” campaign. Now, a new initiative called the Sapporo Wild Salmon Project is being implemented there with the goal of maximizing wilderness of chum salmon. In order to continue conserving and consuming the salmon that grow in the sea, it is important to preserve the rivers where salmon can spawn naturally and produce offspring.

Why Are We Putting so Much Effort into Wild Salmon?

For more than a century, there have been efforts to artificially increase the number of salmon to use as food. In artificial hatchery program, parent salmon that have gone upstream for spawning are captured using fish fences. Their eggs are then collected and inseminated by human hands. Artificially rearing vulnerable salmon fry in this way dramatically increases survival rates before they migrate to the sea. On the other hand, originally, after the salmon migrated upstream the females would dig a hole called spawning redds in the riverbed to lay her eggs. Males who won mating fights release their sperm, and then the females bury their eggs. Finally, the salmon fry hatch in the wild, emerging from the spawning redds in the spring, and find food for themselves from nature. Survival rates during this period are at best about 20% in the wild - just one-fifth that of artificial hatchery program. There are also limits on the carrying capacity of rivers where salmon can spawn naturally. Therefore, salmon breeding in Japan has relied on artificial hatchery programs. However, in recent years, the academic community which is committed to conserving biodiversity has come to view domestication, the phenomenon of species adapting to artificial hatchery conditions, as a problem. I still remember a prominent North American evolutionary ecologist criticized Japanese salmon for becoming "samurai salmon". This was concerns that salmon might evolve to adapt to the hatchery environment, where there is no need for them to lay eggs on their own since humans are opening their bellies to retrieve the eggs. Artificial hatching and stocking is an essential part of the fisheries industry and has cultural value due to its long history. However, if our goal is to conserve biodiversity, we must respect the wild salmon’s way of life.

History of the Toyohira River

Once upon a time, the Ishikari River was the best salmon fishing ground in Ezochi (present Hokkaido). The Toyohira River (in Sapporo City) is a tributary of the Ishikari River. Until around the Meiji era (1868-1912), it saw large numbers of chum salmon going upstream every year to spawn. In the early Showa era (1930th), an artificial hatchery program was implemented in the Toyohira River. Chum salmon fry stopped being released in 1948, but the capture of adult salmon continued until the released fish returned in 1953. The most likely reason for this cessation was the decrease of groundwater in the area. This change meant there was not enough water for the hatchery. Of the 5,499 female salmon captured during this period, 1,677 (30%) were used for egg collection, suggesting that salmon that were being fished as food were also included. After that, official records of salmon from the Toyohira River ceased for more than 20 years. It’s thought that this was brought on by the fact that hardly any salmon were running upstream due to rapid urbanization, which caused the water quality to deteriorate, as well as the construction of river structures.
In the latter half of the Showa era (1970th), the water quality of the Toyohira River improved dramatically due to the rapid development of sewage systems. Despite the lack of official records, there were newspaper reports of chum salmon sightings in the Toyohira River during this time. In 1979, the "Come Back Salmon" campaign, which aimed to return salmon to Sapporo, led to the mass release of chum salmon fry, and a drastic salmon run-up recommenced in the Toyohira River. Fish fences were used to catch adult salmon until 1984, but spawning redds, which are evidence of natural spawning by chum salmon, also began to be observed from this time. From 1990, adult chum salmon were no longer caught, and fish passages were added to weirs that had been an obstacle to the run between 1994 and 1998. As a result, salmon that made it safely to the Toyohira River were able to almost freely spawn naturally.
All chum salmon fry released into the Toyohira River between 2003 and 2006 were fin clipped to determine how well naturally spawned salmon fry are growing. After a few years, it was discovered that 59-76% of the adult chum salmon returning to the Toyohira River were wild fish born from natural spawning. It was also found that the proportion of stray fish from the nearby Chitose River, where a large-scale hatchery program is underway, was almost negligible. These new findings sparked a debate on whether the Toyohira River could sustain salmon returning to the river through natural spawning. In response to this, as well as the academic situation mentioned earlier, we launched the Sapporo Wild Salmon Project (SWSP)¹ in 2014, intending to increase the number of wild salmon in the Toyohira River.

Chronology of chum salmon in the Toyohira River, Sapporo City: Since each female salmon produces one spawning redd, we estimate that the number of spawning redds roughly equals the number of female parents. By assuming a sex ratio of 1:1, the number of spawning beds x 2 provides a rough estimate of the total number of adult salmon.

Sapporo Wild Salmon Project (SWSP) Activities

The Sapporo Wild Salmon Project (SWSP) is a citizens' group that was formed to work with locals to maximize the wildness of chum salmon in the Toyohira River, which flows directly through the Sapporo metropolitan area with a population of 2 million. The group also aims to value the biodiversity of the area, while respecting the traditions of the indigenous Ainu people and the spirit of the past Come Back Salmon campaign.
The first action taken by the SWSP to increase the population's wildness was a reassessment of the number of salmon fry released. Stopping fry releases would increase salmon wildness. However, if this led to an extreme decrease in the number of salmon runs, it would have the unwanted side effect of reducing the opportunities for people to come into contact with salmon. Having salmon running up an urban river like the Toyohira is unique and meaningful by itself. We, therefore, proposed an adaptive management method for the number of fish released based on a scientific perspective, setting a target run of 1,000 fish (around 500 spawning redds). Since 2016, the number of fish released has been reduced to less than half that of prior numbers. The time when those juvenile salmon grow large in the sea and return to the Toyohira River is about to begin in earnest. However, just reducing the number of fry released will not increase the number of wild salmon—the environments where salmon spawn and their offspring are reared must also be conserved and restored. Because the Toyohira River flows through a large city, it requires dams for water storage and flood control, along with revetments and levees for disaster prevention. For this reason, restoring the Toyohira River to a pristine natural environment is unrealistic. However, efforts are being made to restore and preserve spawning environments through collaboration between river managers, river construction contractors, and the SWSP. Although not all of these efforts were successful, we have confirmed that natural spawning has recovered in sections where the spawning environment was rehabilitated.
Monitoring surveys are vital for verifying whether the SWSP's process of trial and error is having a positive effect on increasing the number of wild salmon. From 2016, as part of these efforts, we began thermal marking otoliths of the released salmon. Otoliths are then collected from salmon carcasses, allowing for the identification of wild and hatchery fish. In addition, surveys of out-migrating chum salmon fry are conducted to determine if the salmon fry born from natural spawning are growing.
The SWSP is also involved in outreach activities, aiming to increase opportunities for people to think about wild salmon while deepening their understanding of this species. In addition to activity reports and lectures, the SWSP's Citizens' Forum, held annually, includes research presentations by high school students and a photo contest. This contest was started to involve citizens in research and familiarize people with salmon spawning in the outskirts of the city of Sapporo. In addition, since 2015, the Let's Find Salmon Together! project, which aims to collect photos together with location information, has been ongoing, and has gradually accumulated information on naturally spawning salmon from all over Japan.
Unfortunately, in recent years, the chum salmon catch has been declining nationwide. Although attention is often focused on rising ocean temperatures as a reason for this decline, experts also point out that salmon are also declining in fitness due to artificial hatchery programs, and that the massive reduction of salmon fry occurred in the river before they can reach the ocean. I believe we have to pay the piper for disregarding salmon’s natural habitats by using the salmon hatchery as an excuse. I truly hope that the SWSP's activities will provide an opportunity to reconsider how salmon originally lived. (End)

A survey of chum salmon spawning redds and hotchare (semelparous salmon carcasses　) in the Toyohira River. The SWSP also cooperates with the spawning redd survey, which is mainly conducted by the Sapporo Salmon Museum. The Toyohira River is the only river in Japan where natural salmon spawning has been monitored for such a long period.