Tidewater Goby

Tidewater gobies inhabit lagoons, estuaries, marshes and freshwater tributaries. These habitats have shallow, still, but not stagnant, water. These habitats are freshwater or brackish water, a varying mixture of fresh and saltwater, much of the year. Although they may range upstream a short distance into freshwater, and downstream into saltwater with a salinity of 28 parts per thousand, this species is typically found in salinities of less than 12 parts per thousand. When their habitat experiences an influx of salt water, juvenile and adult tidewater gobies often congregate where freshwater enters the lagoon or estuary.  

Lagoon systems change throughout the season. Coastal lagoon processes in California historically followed a cyclical, seasonal pattern. In late spring, a sandbar forms where the lagoon meets the ocean as the amount of stream flow declines, allowing ocean currents and waves to build up the sandbar on the beach. Waves, often coinciding with high tides, can overtop the sandbar adding seawater to the system. The sandbar creates a barrier, behind which fresh water accumulates, forming a lagoon. During the dry season (late spring, summer, early autumn), freshwater flows are typically insufficient to breach the sandbar. If freshwater flowing into the lagoon becomes low, evaporation can cause a lagoon to become smaller and saltier. Wet season (late autumn, winter, and early spring) rains result in increased stream flows, typically filling the lagoon and may eventually overtop and erode the sandbar resulting in breaching. At which point, the lagoon drains into the ocean. 

The tidewater goby is well adapted to the conditions resulting from the described processes, being able to tolerate and survive extreme conditions while also being able to reproduce quickly when conditions are favorable. When functioning as described, these dynamic systems are so variable that few other fish species survive the extreme conditions. For much of the time during the lagoon’s cycle, tidewater gobies can have few predators or competitors. Tidewater gobies are prey for native fish such as young steelhead, staghorn sculpin, and Sacramento perch, nonnative fish such as bass and centrarchid sunfish, and birds such as egrets, herons, mergansers, grebes, and loons. 

From time to time, flood events can flush individual gobies from their lagoon or estuary into the marine environment; those that survive might return to their original lagoon or they may enter another nearby lagoon if the lagoon is open. Such dispersal to new locations is infrequent and limited due to barriers such as rocky cliffs or man-made jetties. 

Tidewater gobies feed on small, bottom-dwelling, aquatic invertebrates, including various crustaceans, snails, and aquatic insect larvae, particularly lake flies and nonbiting midges. They use three different foraging styles to capture their prey: plucking prey from the substrate surface, sifting sediment in their mouth, and mid-water capture. Tidewater gobies feed at all times of day and are not strictly diurnal or nocturnal feeders. Their food requirements are adaptable to a variety of habitats, an advantageous trait in a fluctuating lagoonal environment.  

Tidewater gobies occur in loosely formed groups of a few to several hundred fish. They swim along the bottom in short spurts, occasionally hovering in midwater or in dense aquatic vegetation. Adult males only construct burrows during the breeding season. They escape predators by fleeing in long dashes into deeper water or aquatic vegetation.  

The tidewater goby is a small, elongate, grey-brown fish. Juveniles and adults are semitranslucent gray, brown or olive with black mottling. Females often appear darker than males, developing black or dark coloring on the body and fins during breeding. Tidewater gobies have large pectoral fins and fused pelvic fins that form a sucker-like disc below the chest and belly.   

Length: 0.6 to 2 inches (1.5 to 5 cm) 

Tidewater gobies are a short-lived species, generally living for only one year, with a few individuals living slightly longer than a year. 

The lifecycle of the tidewater goby is keyed to the annual cycle of the lagoons and estuaries in which they live. While adults can tolerate high salinity levels for shorter periods of time, larval and juvenile tidewater gobies cannot. Reproduction occurs in still water with no to low-salinity and mild-temperatures. The peak of spawning activity occurs during the spring, when lagoons close to the ocean, and again in late summer.  

Tidewater gobies can breed multiple times within their roughly one-year lifespan. When habitat conditions are optimal, tidewater gobies can reproduce quickly, becoming plentiful. Due to being an annual species, if reproductive output during a single year fails, few (if any) tidewater gobies survive into the next year.  

As in many other species of goby, the male tidewater goby constructs a burrow and provides parental care for the eggs. Male tidewater gobies dig breeding burrows in clean, coarse sand, using their mouths to move the sand. The burrows are small, measuring 0.02 inches in diameter.   

Both males and females engage in courtship displays, however unlike other fish species, females complete more intensively than males for access to mates. If there is a limited number of males, females may aggressively spar with each other for access to males that have burrows so that they can lay their eggs. The female will deposit a clutch of 300 to 500 eggs just below the burrow entrance. Once fertilization occurs, the female leaves the burrow, and the male closes himself inside the burrow with a sand plug. The male remains in the burrow guarding and caring for the eggs until they hatch nine to11 days later. 

Larval tidewater gobies live in the mid-layers of the water column for 18 to 31 days while they develop. Upon entering the juvenile and adult life stages, tidewater gobies become substrate-oriented, spending most of their time on the bottom rather than in the water column.