Delta smelt, Hypomesus transpacificus, at the University of California, Davis.
For the first time ever, an annual fish-counting survey has turned up zero Delta smelt—a dire milestone in Bay Area aquatic biology.
This does not mean the fish is extinct—yet—but it does mean that the Sacramento-San Joaquin Delta ecosystem is in disarray. The species, which lives its entire life in the estuary, is a key ecological indicator—and it was prolific until just a couple of decades ago. According to the California Department of Fish and Wildlife’s Fall Midwater Trawl survey
, which provides an annual index on abundance for several fish species in the Delta, the Delta smelt index generally averaged several hundred fish into the early 2000s. Then, in about 2003, numbers of Delta smelt, as well as several other native fishes, began to plunge. To Jonathan Rosenfield, the lead scientist with The Bay Institute, it’s clear what’s going on. “The one thing that has significantly changed in the past few decades is that we’re taking a lot more water out of the Delta
now than we were then, and the fish have responded dramatically,” he said. In 2003—the year the collapse began—the powerful pumps at the southern edge of the Delta revved into full throttle and for four years in a row took record volumes of water—more than 6 million acre-feet per year, mainly to support farms in the San Joaquin Valley. That’s four times the average annual water diversions back in the 1960s, when the annual trawl survey began. The Delta smelt’s decline
has paralleled similar trajectories in winter-run and spring-run Chinook salmon, steelhead trout and green sturgeon. Habitat loss and dams have played a role in these declines, but Rosenfield says water removals—lately averaging a more modest 3.5 million acre-feet each year—must not be dismissed as a main factor. “These are all very different species,” Rosenfield said, “and the main things they have in common is they’re all endangered and they all live in or migrate to this estuary.”
Photo: Joel Sartore, National Geographic, the Photo Ark