Fast Facts: Unarmored Three-spine Stickleback, Southern California’s Small, Endangered Fish

LOS ANGELES—Southern California’s unarmored three-spine stickleback has made headlines periodically, most recently over a lawsuit that was filed on Jan. 18 by the Center for Biological Diversity against the Trump Administration for allegedly failing to take measures to protect the endangered fish. What is the three-spine stickleback and what is going on with the fish?

The three-spine stickleback is a two-inch-long fish with three spines on its back. The stickleback feasts on insects found on the bottom of riverbeds, small crustaceans, and snails. They reproduce throughout the year in slow-moving water under the cover of aquatic vegetation. While the unarmored three-spine stickleback used to inhabit many freshwater systems in Southern California, populations are now limited to relatively few stream networks within Santa Barbara, Los Angeles, San Bernardino, and San Diego counties, according to Los Padres Forest Watch.

The unarmored three-spine stickleback was listed as endangered in 1970 under the precursor to today’s Endangered Species Act. Critical habitat was proposed for the species by the U.S. Fish and Wildlife Service in 1980, but never designated. In 2002 the Center for Biological Diversity filed a lawsuit to protect habitat for the stickleback, since Fish and Wildlife Service failed to finalize its more than 20-year-old proposal. The Center lost the suit when the Service “finalized” the proposal by withdrawing it.

“We continue to watchdog development on the river and advocate for the tiny, pugnacious fish through our work to protect Southern California watersheds and forests,” the Center wrote on its website.

According to a five-year review completed by the U.S. Fish and Wildlife Service in 2009, the stickleback historically was found throughout a much larger area including the Los Angeles, San Gabriel, and Santa Ana Rivers, but were extirpated from these areas as a result of of urbanization.

“The ongoing effects of urbanization, eutrophication, stream channelization, addition of water, groundwater removal, and water quality, are the most critical threats to the habitat of the UTS; substantial reduction or elimination of these threats is not expected in the near future,” the Fish and Wildlife Service wrote in the 2009 review.

The fish also made headlines in 2009, as environmental advocates fought against a proposal by Cemex, a cement company, for a project that would pump water from the Santa Clara River to its mining project in Southern California. Stickleback habitat protection advocates argued pumping would increase the frequency that the Santa Clara River dries up, which could lead to more stickleback getting stuck in isolated pools when the river is dry.

The fish also made headlines in 2017, as its protection became part of a deal for a housing development project dubbed the Newhall Ranch project in northeast Los Angeles County, according to the Daily Pilot.

According to Aquarium of the Pacific, three-spine sticklebacks have recently become a major research organism for evolutionary biologists trying to understand the genetic changes involved in adapting to new environments. Scientists believe that the many different stickleback populations in the northern hemisphere all emerged from a common marine ancestor.

“After glaciers receded, sticklebacks colonized widely divergent habitats in addition to the ocean, including freshwater lakes and rivers throughout the northern hemisphere,” the Aquarium of the Pacific wrote on its website.