U.S. says Bay Area delta’s longfin smelt could become extinct

Federal biologists have concluded that another native fish of the Sacramento-San Joaquin River Delta is headed toward extinction, underscoring the region’s severe environmental problems.

The U.S. Fish and Wildlife Service announced Thursday that it has determined that longfin smelt in the delta deserve Endangered Species Act protections. But the finding won’t expand restrictions on the delta’s water operations because the agency is simply designating the fish a candidate for listing.

The longfin is joining 251 other species across the country that the service deems in peril but that are in line behind higher-priority listings.

The move is a reversal for the wildlife service, which in 2009 denied a petition to list the San Francisco Bay-delta longfins, saying they weren’t distinct from other longfin populations on the West Coast.

In a legal settlement with two environmental organizations, the agency conducted more research and concluded that ocean currents and the small fish’s limited swimming abilities kept the bay-delta longfins from mingling with other groups, making them a discrete population in danger of extinction.

“It’s about time,” said Gary Bobker, program director of the Bay Institute, one of the groups that sued the government. But without actual listing, he said the fish’s prospects won’t improve.

It is not clear what, if any, additional protections would follow listing, since biologists attribute the plunge in longfin numbers to many of the same conditions hurting its relative, the delta smelt, which enjoys endangered species protections that have restricted delta pumping.

Those factors include decreased freshwater flows, pollution from a large regional wastewater treatment plant and an invasive clam that consumes the plankton that are a major smelt food source.

Fish and wildlife officials said mortality at the big delta pumps is less of a problem for longfins than delta smelt and that the seasonal flow requirements of the two species are somewhat different. Bobker said that could mean that additional restrictions on water diversions are necessary to save the longfin.

Distinguished from other smelt by their long pectoral fins, longfins are more tolerant of ocean water than delta smelts and swim farther west, into San Francisco Bay and beyond. They were once among the most abundant fish in the bay-delta system, but their numbers are a fraction of what they were 25 years ago.

bettina.boxall@latimes.com