Above: EDSM crew retrieving a net during trawling in Montezuma. Photo by Kate Erly.
The robust monitoring programs established to track now-rare Delta smelt could benefit other native fishes, too.
Decades ago, resource managers first learned of declining Delta smelt numbers not through surveys targeting the once-abundant native fish, but rather as a byproduct of long-term monitoring programs for non-native striped bass. Now, the authors of a new study
published in the March 2021 issue of San Francisco Estuary and Watershed Science advocate for the use of bycatch data from the recently established Enhanced Delta Smelt Monitoring (EDSM) program to better understand juvenile Chinook salmon distribution. “The scope of [this multi-million dollar Delta smelt survey] has not really been seen before in the Estuary," says lead author Brian Mahardja, a biologist with the US Bureau of Reclamation, "that’s why there was a call to see what else we can gain out of this program.” The study team, also representing the US Fish and Wildlife Service and the California Department of Water Resources, analyzed juvenile Chinook salmon bycatch data collected through the EDSM to assess its potential to augment data obtained through other fish surveys. They found that some under-sampled regions of the Delta see improved coverage through EDSM, and that the program’s boat-based, labor-intensive random sampling technique “can provide more statistically robust abundance estimates relative to traditional methods.” That said, the authors also concluded that the use of fixed sampling stations and low-tech methods like beach seining, in which a net is operated manually from shore, still provide a cost-effective way to monitor salmon occurrence in certain parts of the Estuary. “The take-home point is about the trade-offs of different sampling methods,” Mahardja said. “It costs a lot to run these programs, and we want to make sure that we’re getting as much as we can out of them.”