December 1, 2017
Simple Technology Helps to Answer Big Questions About Salmon
With an ever so slight mechanical whir powered only by the flow of the San Joaquin River, Restoration Program staff brought the first rotary screw trap of the season to life this month – part of a larger effort to populate the river with salmon like those extirpated decades ago. In the coming months, staff hope to have the traps fill with newly emergent juvenile spring-run Chinook salmon fry, parr and smolts – the result of releasing 115 adult spring-run Chinook salmon into the river months earlier. And, as recent results indicate, spring-run Chinook salmon are spawning in the San Joaquin River for the first time in more than 60 years: over 350 fry have been recovered so far.
After being caught, the juvenile fish are measured, weighed and have a tiny tissue sample taken for genetic identification before they are released back to the river. The genetic information gathered helps Program biologists determine the parentage of each fish in the river. The value of this information is two-fold: a better understanding of which fish have the genetics for the greatest chance of survival in the San Joaquin River ecosystem; and, the ability to track the fish back to a specific redd (fish nest) in order to analyze which locations have the best survival rates and why.
The adult salmon – the parents of the newly emerged fry – were grown to adult size over the course of three to four years in tanks at the Salmon Conservation and Research Facility, located on the banks of the San Joaquin just below Friant Dam. These full-grown fish were then released into the river and some spawned, producing their offspring before dying.
Though these adult salmon never migrated to the ocean or journeyed back upstream as natural salmon do, they still constructed 16 redds in the most upper reach of the river that were detected through observation.
The rotary screw traps, essentially large metal mesh cones which funnel fish from the river so they can be counted, studied, tagged and released, are deployed in key locations of the San Joaquin River in order to better understand the spawning success. The traps can help to reveal not only survival rates, but the timing of capture, associated water flow rates and temperatures at the time of capture and which river locations are preferred by salmon. All of this information will help the Restoration Program to better understand what it takes to bring salmon back to the river.
In the coming months, Program staff also will conduct electrofishing and deploy netting techniques to monitor the lower reaches of the Restoration Area for potential steelhead in the river.
Listen to Valley Public Radio’s story about spring-run Chinook salmon monitoring and more about the Program here!