Before the construction of Friant Dam and creation of Millerton Lake in 1942, the San Joaquin River was a historic spawning habitat for spring-run Chinook salmon.
But it’s been more than 65 years since adult salmon returned from the Pacific Ocean to the river – until this month, that is.
So far in April, five adult Chinook salmon have been discovered in the same area of the San Joaquin River for the first time in decades. Josh Newcom, a spokesman for the U.S. Bureau of Reclamation’s San Joaquin River Restoration Program, said the salmon were all caught in net traps in an area of the river’s lower Eastside Bypass.
“This is monumental for the program,” said Donald Portz, manager of the restoration program. “It’s a clear indication of the possibility for these fish to make it out of the system as juveniles and then return as adults to spawn.”
The first of the five fish was caught on April 9. Scientists collected tissue samples and an acoustic tag was inserted down the fish’s throat so they could track its movements before they released the salmon into a portion of the river called Reach 1, a 40-mile stretch downstream from Friant Dam.
Two fish were caught on April 19, and two more were caught this week – one on Tuesday, another on Wednesday – in the same part of the Eastside Bypass.
Scientists could determine that all five salmon were from California hatcheries, and not wild fish, because their adipose fins – a small fin on the back between the dorsal fin and tail – had been removed.
Additionally, one of the two fish caught on April 19 did not survive, and biologists were able to recover a coded wire tag embedded in its snout that confirmed it was one of more than 38,000 juvenile spring-run Chinook released into the river two years ago, in March 2017.
Spring-run Chinook get their name from the March-through-June period when they leave from and return to the river system where they are spawned, according to the restoration program.
Adult salmon inhabit the river’s cool upper reaches during the summer and spawn in the fall. After hatching and growing to juvenile stage, where they are about the size of a human hand, some fish migrate to the ocean or remain in the river for a year before migrating. Salmon spend two to five years maturing to adulthood before returning to the river, according to biologists.
Additional tissue testing will be conducted to determine if any of the fish were spawned at a state hatchery along the river downstream from Friant Dam.