Over the December 10th weekend, five agencies came together to release Delta Smelt into the Sacramento River. Members of UC Davis, Department of Water Resources, California Department of Fish and Wildlife, US Fish and Wildlife Service and the United States Geological Survey (USGS) positioned and secured large cages in the river down by the old Army Base. Cameras were then placed around the cages by the USGS that would capture the release on a type of sonar which would show the responses of the Smelt at the point of release to see how they respond to the current and if they group together or swim off by themselves.
Then over the next few days, approximately 6,400 Delta Smelt, in keg-like barrels (as seen in the picture), holding 200 – 250 fish each were deposited into the positioned cages. The following day, 6,400 more were taken out to the site. The goal was to release around 12,800 fish in total. There were many trips from the Public Dock by City Hall to the cages and back.
The releases were done in two phases. There was a “soft release” where the Smelt from the cages were released. A “hard release” was made by releasing Smelt directly into the river without acclimating inside the protective cage. In an effort to tell the two groups apart, one of the groups were tagged by either having a small dorsal fin clipped or a tag injected directly under the top layer of skin.
This release was an important step in bringing the Delta Smelt population back up. It has taken about 5 years to get them to successfully breed in captivity and this is the first generation to do that. Now that the scientists have solved that problem, they will now focus on releasing the fragile fish into the Delta, hoping for a thriving population.