Even in flood, smelt captured at Delta pumps

U.S. Fish and Wildlife Service

State and federal water exporters are approaching a key limit to the number of imperiled Delta smelt that can be “salvaged” (read: killed) at the south Delta pumps.

Make no mistake, it’s been a great water year for people and fish alike. Conditions in the Delta for smelt and other species are the best they’ve been in years.

But for reasons experts can only theorize about, smelt have been showing up at the pumps off and on since January. As of today, 57 smelt have been counted there; this year’s “take” limit, as determined by scientists, is 64 fish.

If you bust through your take limit you risk getting shut down. So the U.S. Bureau of Reclamation has asked its counterpart, the U.S. Fish and Wildlife Service, to consider raising the limit. (The state’s not pumping right now because of damage at Clifton Court Forebay.)

No decision has been announced. But in its March 17 response to the bureau’s request, Fish and Wildlife notes that the exporters’ planned operations through April “will maintain favorable conditions for Delta smelt” and says the agency will work closely with the exporters to “adaptively manage and avoid or minimize impacts.”

Salvage at the pumps. Graph from the state Department of Fish and Wildlife

Jon Rosenfield, a biologist with The Bay Institute, an environmental group, expressed a word of caution about increasing the number of fish that can be killed. The limit was set at 64 for a reason, because the science considers that to be the number of fish that can be taken at the pumps without jeopardizing the species, he said.

“There has to be a biological rationale for allowing more take than would previously have prevented jeopardy,” Rosenfield said.

Rules for how much water must flow through the Delta were temporarily weakened each of the past three years because of the drought, and smelt populations reached new historic lows. The population will likely increase this year, but every adult smelt taken at the pumps is one less fish available to produce next year’s progeny.

“We need to capitalize on every opportunity we have to bolster their populations,” Rosenfield said.

Non-scientist that I am, I was surprised to learn that smelt were showing up at the pumps at all. I’ve been told they’re lousy swimmers. And with all the water in the system, the rivers near the pumps have been flowing downstream (a rarity) for weeks now. Wouldn’t that keep smelt at a safe distance?

Not necessarily. Rosenfield said that even with rivers surging in one direction, smelt may be able to work their way upstream following smaller eddies or side currents.

Why swim upstream at all? The smelt may be chasing turbid, or cloudy, water into the area around the pumps, he said. Smelt like turbidity because it allows them to hide from predators. They may be wandering close to the pumps because (gasp) the south Delta actually appears to the fish to be a functioning river estuary right now.

We won’t have the full picture for how this year’s high flows have benefited smelt until a series of surveys this fall. A word of caution: Smelt populations increased 738 percent during the wet year of 2011, only to plummet right back to near-historic lows the following year once dry conditions returned.

If there’s a nice bump in 2017, let’s hope it isn’t another one-time deal.

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