Remember those young salmon trucked to the ocean in 2014 and 2015? During California’s drought, water agencies reduced water flows and rivers became too hot and dry for salmon to migrate from their spawning sites to the ocean. They were hauled in trucks instead of swimming downstream and apparently they missed out on imprinting on their route. This fall, some of these salmon became lost as they swam upstream through a river they never traveled and, as a result, didn’t arrive home to spawn.
In Do anadromous fish dream of Ubering home? last January, I wrote about the salmons’ unusual migration method and the questions fisheries biologists held about the consequences.
Salmon imprint on their home using magnetism and scent as they swim downstream to the ocean. Years later, this imprint guides anadromous fish back to where they hatched as they travel inland from the ocean to their spawning grounds. Their arduous journey against strong currents and rapids can cover hundreds of miles up many thousand feet in elevation. Traditional salmon survived the upstream migration for millennia but humans have added obstacles.
Contemporary salmon living in a human-dominated landscape might begin life in hatcheries and travel to the ocean in trucks, thus missing the chance to learn the imprint of home. Biologists wonder how many trucked salmon will swim upstream and find natural spawning grounds or reach the hatcheries. In the past few years, this question was especially pertinent when drought conditions meant all hatchery salmon migrated inside the steel climate-controlled tank trucks. [...]
The recent drought in California, diminished habitat conditions making downstream migration dangerous or impossible. For two years all the salmon raised each year — 30 million Chinook salmon — traveled by truck from Sacramento River basin hatcheries to the ocean.
It was either hitch a ride or die in the hatcheries. Fisheries biologists were uncertain about the consequences of circumventing the migration by trucking salmon to the ocean but knew it was the only viable option. They had questions, though.
- Does iron in the steel fish tanks or electrical cables in hatcheries disrupt salmon’s magnetic GPS system?
- How many of them will be able to find their way home?
- How do salmon define home when they began in a hatchery tank and migrated in a truck?
Some of these questions were answered this fall when the chinook salmon trucked to the ocean were ready to make the return journey to their spawning grounds. Chinook salmon live two or three years in the ocean and now are mature. It was time for them to migrate to the five Central Valley hatcheries located below dams that block upstream spawning grounds once used by salmon.
Fish successfully returned to four of the five hatcheries this fall. However Coleman Hatchery, the most productive, had fewer salmon return and produced six million fish, half as many as usual. And to reach even that number trucks had to transport eggs from the hatchery where some of Battle Creek’s salmon mistakenly arrived. The Coleman Hatchery is located 280 miles from the ocean at Battle Creek outside Red Bluff, in the far northern end of the Central Valley. This is the furthest inland salmon migration route among all the CV hatcheries and bewildered salmon instead travelled to hatcheries closer to the ocean.
Biologists said the trucking process badly disoriented almost all of the young fish when they returned as adults.
As many as 143,000 adult fish will return to the Coleman hatchery to spawn in a normal year. In 2017, only around 3,000 adults returned, enough to fertilize about 4 million eggs – well shy of the hatchery’s 12 million goal.
Many of the wayward adult fish hatched at Coleman actually ended up at the state’s Nimbus Hatchery on the American River in Rancho Cordova. Biologists know they were Coleman fish because they insert specially coded wire tags the size of a pencil tip into a percentage of hatchery smolts.
This fall, state and federal biologists were able to gather an additional 2 million fertilized eggs at Nimbus from the Coleman fish that got lost and ended up there. Those eggs were transported to Coleman.
The question is whether having just 6 million fish at Coleman will translate into worse fishing seasons in the years ahead.
Despite the dams blocking the rivers salmon historically used for spawning, the hatcheries previously kept fall and late-fall chinook salmon runs healthy enough to not meet criteria for listing under the Endangered Species Act. Winter-run is listed as Critically Endangered and spring-run is Threatened. Overall, returns of salmon born during the drought and trucked to the ocean are among the lowest ever recorded.
While the fall-run chinook are a $1.4 billion economy for California, the low return numbers affect more than humans. Salmon runs are critical to wildlife and ecosystems. More than 40 species of vertebrates, including salmon, trout, birds and mammals feast on salmon, their eggs, carcasses, or their young. Even the dead salmon remaining after spawning release nutrients back into the ecosystem. Up to 40 percent of the nitrogen in streamside plants is from salmon. Predators and scavengers move nutrients far from the water into upland habitats.
Losing salmon is more than losing an important NorCal economy because new industries and jobs can take the place of commercial fishing. Ecosystems are irreplaceable. Salmon are a keystone species in both aquatic and terrestrial habitats. They influence and mirror the survival of these ecosystems. Trucking was necessary because of drought and state water management policies. Keeping salmon runs healthy required experimentation.
This year’s results indicate that the 2014-15 experiment is dangerous to salmon population survival. We cannot control droughts — they will occur, perhaps more frequently and severely due to climate change. Instead of relying on trucks, we should change how we manage water resources. We need to allocate more of the reservoir water held behind dams to flow into the rivers and streams. Healthy river flows will allow young salmon to swim downstream to the ocean and imprint on home so, years later, they can find their way back to spawn.