With populations of numerous endangered Delta fish species at alarming lows, officials in California are planning a number of steps to help them survive if 2015 proves to be a fourth drought year.
The California Department of Fish and Wildlife last week released the results of its annual fall population survey for five key fish species in the Sacramento-San Joaquin Delta. It showed that Delta smelt, a small endangered fingerling, reached its lowest population level in nearly 50 years of monitoring.
Other species did not plunge to record lows but came close. Longfin smelt and American shad both recorded their second-lowest numbers, while striped bass and threadfin shad were at their third- and sixth-lowest levels, respectively.
Mark Cowin, director of the California Department of Water Resources, called the depleted fish populations “a very deep concern,” not only for fisheries, but because they can trigger provisions in the Endangered Species Act that restrict water diversions from the Delta.
The estuary, the largest on the West Coast of the Americas, provides drinking water to about two-thirds of California’s population and irrigation water for some 3 million acres of farmland.
“It’s real clear that the longer the drought persists, the more acute its effects are,” Cowin said. “That applies to fish and wildlife; it applies to water users; it certainly applies to our agricultural economy. I’m concerned on all of those fronts.”
The fishery numbers are not entirely surprising because all five species are known to decline in drought years. They are pelagic species, meaning they depend on constant freshwater flow through the estuary. When those flows decline, so does fish abundance.
DWR, the U.S. Bureau of Reclamation, and three state and federal wildlife agencies last week released a “Drought Contingency Plan” that outlines numerous steps to stretch water supplies and protect fish species this year. The plan also applies to salmon, which have slightly different needs than resident species in the Delta.
The agencies produced a similar contingency plan last year, but this one has been rolled out much earlier in anticipation of a worsening drought.
Among the measures planned are “early warning” fish sampling in Delta waters to determine where fish are located and where they are moving. This began in December and will continue through April. The primary goal is to guide water diversions from the Delta to avoid drawing sensitive fish such as smelt into water-export pumps.
The process is similar to the annual population surveys, which involve towing a net behind a boat and counting the fish it captures to calculate abundance. Officials also have begun using a high-tech “smelt cam” to count fish in a less invasive manner. The “smelt cam” uses a net like a funnel to direct fish through a special underwater camera without being captured. Computers use the imagery to identify and count the species.
To help in this effort, some hatchery-raised winter-run salmon – an endangered species – will be implanted with electronic tags to track their progress downstream. Sensors will be installed at regular locations along the Sacramento River that will send out an acoustic signal to “ping” the tags in the fish. This will help track the run’s progress downstream, which will allow officials to time water releases as well as water diversions in the Delta to avoid killing salmon in the pumps.
Last year, the State Water Resources Control Board adjusted salinity rules in the Delta so DWR and Reclamation could avoid releasing precious cold water stored in upstream reservoirs. One rationale, besides preserving the water for human consumption, was to retain cold water behind the dams to support salmon runs later in the year.
It appears the move was not entirely successful, as the abundance of winter-run salmon migrating downstream was the lowest in at least 12 years. Also, many of the nests, or redds, where salmon eggs incubate in riverbed gravels either dried up or became too warm at critical times due to low flows.
This year, officials plan similar efforts to retain cold water behind dams, if necessary. To monitor salmon redds better, the plan calls for installing probes in the Sacramento River where redds are present to better monitor water temperature and dissolved oxygen content.
Although the drought contingency plan includes many steps to help fish, it makes plain that the top priority is to preserve water supplies for human needs, a point also emphasized by DWR’s Cowin.
“Our first priority is to make certain that we have enough water in reserve and are able to meet the very basic human health and safety needs,” he said.
Saving all that cold water behind dams had at least one negative consequence last year. Downstream, it deprived the Delta of water flows that may have been helpful at critical times for smelt, striped bass and the other pelagic species, Rosenfield said.