Watching a predator eat an endangered species is always awkward. Should you intervene? Yell, wave your arms, throw things? I went through that train of thought a couple of years ago as a great blue heron and a great egret ate their way through the California red-legged frog population of a small stock pond at Point Reyes.
It happened again last month at Rodeo Lagoon in the Marin Headlands, again with a great blue heron and great egret that were noshing on small fish. I couldn’t get a good look at the prey as they went down the birds’ throats; they could have been threespine sticklebacks or prickly sculpins, both of which occur there. Odds are, though, they were tidewater gobies, federally listed as endangered in 1994. When biologists sampled the lagoon in 2005, 99 per cent of all the fish they caught were tidewater gobies.
The total catch, if you’re wondering, was 9314 fish of all species, which would work out to 9220 tidewater gobies. That sounds like a healthy population for an endangered creature—but not if you consider the goby’s life history. It’s an annual creature; each generation of gobies hatches, feeds, mates, and dies within a year. 2005 happened to have been a boom year, ironically because algal blooms in the lagoon reduced dissolved oxygen to levels that other fish could not survive.
These are eccentric little guys with an unconventional reproductive strategy. Among sexually dimorphic fish species, males are typically larger, more brightly colored, and more aggressive than females. This syndrome is reversed in the tidewater goby, where females wear the bright colors and compete for access to males. Female-female combat often involves “fin displays, tail-beating, charging, biting, jaw locking, and wrestling,” according to ichthyologist R. O. Swenson.
Males dig spawning burrows in territories they defend from other males. Females defend the territory around their chosen male from other females. I can’t resist quoting Peter Moyle’s account in Inland Fishes of California: “A female tests the readiness of a male to mate by trying to enter the burrow or sticking her head into his mouth. One response is for the male to retreat into the burrow and plug the entrance with sand. Another is to let the female enter. Once a pair is in a burrow together, the male usually plugs the entrance with sand and the pair remains in the burrow together for 1-3 days.” Like a “Do Not Disturb” sign on the hotel room door, or, for those of us who were there then, a necktie on the doorknob of the dorm room.
After the honeymoon, the female goby digs her way out, leaving behind fertilized eggs attached to the burrow wall. The male replugs the entrance and spends the next ten or so days fanning and rubbing the eggs until the fry hatch. When they do, they swim away to, as Moyle puts it, “join the plankton.” This is something many of us have done or at least considered at some point in our lives.
Brackish stream-fed coastal lagoons from Del Norte County to San Diego are the tidewater gobies’ habitat of choice. Their numbers build up in summer while a sandbar separates their home lagoon from the ocean and drop in winter when the barrier is breached. The goby population in Santa Ynez Lagoon (Santa Barbara County) went from a peak of 11 million to a nadir of 11,000 in a single year.
The fatal flaw in this adaptive strategy is that each lagoon’s population is on its own. Between a quarter and a half of the species’ known populations have been lost in the past century as a result of the diking and draining of estuarine wetlands, sediment buildup in lagoons, or permanent tidal breaching through jetty construction. Predators (including gobies of exotic Asian species) and pollutants also take a toll. By the most recent estimate, only 41 historic locations still have gobies. As local populations wink out, the likelihood of recolonizing vacant lagoons diminishes. Isolated populations diverge from each other genetically, fragmenting the species’ gene pool.
Since 1994, environmentalists, lawyers, and bureaucrats have been wrangling over the extent of the protection to be given this small obscure fish. The most recent round went to the goby and its advocates last October, when the US Fish and Wildlife Service expanded the amount of protected habitat by 20 percent. This includes ten currently unoccupied lagoons, some in Marin and San Mateo counties.
I’ve heard from folks like historical ecologist Robin Grossinger that there’s potential for restoring this species in parts of the East Bay as well. It would be good to have them back. The tidewater gobies isn’t charismatic or economically important, but it’s a fascinating product of evolution—a solution to the problem of being a fish in a marginal, unstable environment. “Life is good, whether stubbornly long or suddenly a mortal splendor: meteors are not needed less than mountains,” wrote Robinson Jeffers.