Week of February 13, 2023

After hav­ing intro­duced the 4,500 Fall run (all PIT tagged) and 100 Late-Fall year­lings (all PIT and JSATS tagged) into the fields the pre­vi­ous week, empha­sis has turned to uti­liz­ing the net­work of sev­en PIT read­ers at the rice box­es to col­lect data on fish move­ments with­in the field and out the field drain.  All 4,500 Fall run were released into the 2nd to high­est check in the field.  There­fore, to exit the field these fish had to swim through at least three sets of mod­i­fied rice box­es.  The day after intro­duc­tion about 125 of the 4,500 salmon had exit­ed.  This ini­tial exo­dus of a small but notable per­cent­age of fish in the first 24–48 hours is a known phe­nom­e­non.  By Day #2, how­ev­er, the num­ber exit­ing dropped sharply to about 32 demon­strat­ing that over 4,300 of the 4,500 fish were set­tling into the field to enjoy the pop­u­la­tions of float­ing bugs for them to eat.  Includ­ed in the visu­als for this week is a pic­ture and a short video of this nutri­tious float­ing smor­gas­bord of deli­cious zoo­plank­ton for the salmon to dine on while in the field.  Like the pre­vi­ous year’s field sea­son, we quick­ly demon­strat­ed the abil­i­ty of these fish to effec­tive­ly move through the mod­i­fied rice box­es with the holes and notch­es with­in just one day.

The UC Davis sci­ence team con­tin­ued count­ing and releas­ing fish dai­ly from the fyke and con­duct­ing sein­ing oper­a­tions. We had count­ed about 90 nat­ur­al-ori­gin salmon by this time. Based on salmon size-class assess­ment, we sus­pect­ed we had count­ed most­ly Fall run (about 75), 1 late-Fall run, 8 Win­ter run and 3 Spring run dur­ing sein­ing and fyke net trap oper­a­tions. We have added three more fish (under­lined in this week’s update) to the list of oth­er fish­es observed includ­ing split­tail, shad, gold­en shin­er, Sacra­men­to suck­er and hatch­ery steel­head with­in the study fields.  Occa­sion­al preda­tors include bass, sun­fish, pike min­now.  As men­tioned pre­vi­ous­ly, the larg­er preda­tors were sam­pled for diet con­tents via gas­tric lavage, some PIT tagged and released.  

The UC Davis Team had also suc­cess­ful­ly deployed all the JSATS receivers in the bypass canal, both upstream and down­stream, so were ful­ly pre­pared to mon­i­tor JSATS-tagged fish move­ment with­in the bypass.  

Tem­per­a­ture and DO mon­i­tored con­tin­ued, in real-time, with autonomous HOBO data log­gers and there were no mea­sure­ments of con­cern by that time even though a cou­ple of dai­ly tem­per­a­ture read­ings were in the high 60’s.

The grow­er con­tin­ued to be able to reli­ably main­tain the desired flood depths of 10–12 inch­es in each check.  

The UC Davis Team sein­ing towards the fyke net at the field drain to make sure all fish in the canal move into the fyke net.
Picture of a JSATS receiver out of the water in the drainage corridor from the field into the Sutter Bypass. Upon final field drainage this will be submerged and detecting the JSATS-tagged late-Fall Run Yearlings as they leave the field.
Pic­ture of a JSATS receiv­er out of the water in the drainage cor­ri­dor from the field into the Sut­ter Bypass. Upon final field drainage this will be sub­merged and detect­ing the JSATS-tagged late-Fall Run Year­lings as they leave the field.
The UC Davis Team col­lect­ing fish from the fyke net below the field drain.
Sample of water from the field full of zooplankton (high-quality fish food).
Sam­ple of water from the field full of zoo­plank­ton (high-qual­i­ty fish food).
Team pro­cess­ing a PIT-tagged fish found in the fyke net.
PIT-tagged fish found in the fyke net being identified with a PIT reader.
PIT-tagged fish found in the fyke net being iden­ti­fied with a PIT read­er.
Bot­tle of water from the field lit­er­al­ly “alive” with deli­cious swim­ming zooplankton—exactly what baby salmon need to eat.
Data on movement of PIT-tagged fish being downloaded for analysis.
Data on move­ment of PIT-tagged fish being down­loaded for analy­sis.
Expla­na­tion of the oper­a­tion of the PIT read­er sys­tem locat­ed at the field drain.
Data on PIT-tagged fish exiting the field being downloaded.
Data on PIT-tagged fish exit­ing the field being down­loaded.
Expla­na­tion of ongo­ing mon­i­tor­ing of tem­per­a­ture and dis­solved oxy­gen in the field at mul­ti­ple loca­tions.
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