Fluctuations and Recolonization of Federally Endangered Tidewater Goby Populations in Coastal Southern California, 1975-2007

Since the mid-1970s San Mateo Creek lagoon (4-6 ha), northern San Diego County, CA, was sampled to monitor populations of the federally endangered tidewater goby, Eucyclogobius newberryi, and to remove non-native aquatic species.  Sampling frequency increased from 1996-2008.  Six other nearby lagoons (0.5-70 ha) were sampled from 1996 to 2002.  All of the lagoons were in a relatively natural state within Marine Corps Base Camp Pendleton.  Lagoons opened to the ocean by winter runoff typically close behind barrier sand berms during the 7-9 month dry season (spring to early winter) of the Mediterranean climate cycle.  In low rainfall years the lagoons may not open and can revert to a brackish or freshwater condition which leads to increase in tidewater goby populations.  Historically threespine stickleback and juvenile steelhead also occupied some of these lagoons.  Larger lagoons maintain more salinity and larger populations of other estuarine fish species.   While closed conditions are favorable for tidewater gobies, several non-native, freshwater, predatory species can invade the lagoons under low salinity conditions.   The strong flushing flows of wet years greatly reduces the native and non-native fish populations but allows re-invasion of more estuarine species changing the fish community of smaller systems to the conditions more typical of larger lagoons.  Management of these lagoons for federally endangered tidewater gobies, as well as for federally endangered steelhead and native threespine stickleback, will require attention to natural cycles of lagoons and their effects on the success of both native and non-native aquatic species.  Non-native centrarchid sunfishes and ictalurid catfishes have likely been responsible for two extirpations of the tidewater goby population at San Mateo lagoon.