Cooperative Fish and Wildlife Research Units Program: California
Education, Research and Technical Assistance for Managing Our Natural Resources

The tidewater goby (Eucyclogobius newberryi) is a federally endangered fish species ranging from the Smith River in northern California to Agua Hedionda Lagoon in southern California. The tidewater goby inhabits brackish/freshwater lagoons and estuaries that are positioned linearly along the California coast. Lagoons and estuaries inhabited by tidewater goby are separated from one another by 1 - 20 km. Tidewater gobies have no explicit marine stage and ocean inhabitants between these estuaries and lagoons are not inhabited by a stable populations of goby; however, rare periodic migrants occur in ocean habitats. There is only one known record of tidewater goby from coastal oceanic waters. Many coastal lagoons inhabited by tidewater gobies are physically isolated from the ocean by sand bars that rarely open to the ocean (~0 - 5 openings annually) making dispersal into and out of the lagoons contingent upon lagoon openings. Given the fragmented nature of tidewater goby geographic distribution it is convenient to view this species as composed of metapopulations experiencing periodic local extirpation with subsequent recolonization from regional source populations. Currently, there is uncertainty regarding metapopulation dynamics of tidewater goby populations from Humboldt Bay, California. Previous investigations of the federally endangered tidewater goby in the north coast region of California showed that artificially fragmented populations within Humboldt Bay exhibited higher genetic differentiation and lower genetic diversity relative to naturally fragmented populations. It was unclear whether these patterns were the result of multidecadal isolation and lack of migration among geographically separated populations or if periodic recolonization of fragmented habitats combined with founder effects (e.g., metapopulation dynamics) were responsible. Determining which process is operating will provide insights into the extent of migration between discrete and isolated Humboldt Bay tidewater goby populations. Such information is key for management because it would indicate the likelihood of re-colonization of extirpated populations.