Trucking juvenile salmon from Central Valley hatcheries to areas downstream of the Delta is known to increase overall fish survival. This is a vital program in maintaining a viable commercial and recreational fishery, and escapement back to the Central Valley. However, that action can also increases straying of adult fish to non-natal areas which is considered undesirable.
Trucked fish are placed into net pens for a few hours to allow them to recover from stress and adapt to the salinity and temperature conditions at the nets. If the fish arrive in good shape from the hatchery, survival is estimated to be near 100% at the net locations. Recently hatchery managers have used release sites for a maximum of two days before switching to alternative release locations due to predators homing to the site after two days. After a five day rest, a site can be used again. This has greatly increased survival of fish formerly released on day three and beyond. Other release improvements include releasing from the net pens on the outgoing tide in mid channel and releasing late in the day when predatory birds have stopped feeding for the day.