on each side of the caudal fin base and G. bosci 

 is entirely scaleless. The best field character- 

 istic for differentiating the two species is the 

 color pattern on the sides of the body. In G. 

 bosci, the sides are dark with eight or nine nar- 

 row, light bars that are of uniform width, and 

 there are no dark spots along the lateral midline. 

 During the breeding season the light bars of some 

 males are obscured by increased pigmentation. 

 In G. ginsburgi, the light bars broaden below 

 the lateral midline, and there are dark spots or 

 lines where the midline crosses the dark bars. 



G. bosci and G. ginsburgi occur in large oyster 

 reefs and small isolated patches of oysters that 

 are partially exposed at low tide. The total area 

 occupied by the small patches is relatively great 

 since they border the maze of tidal creeks and 

 occupy shallow mud flats in the lower reaches 

 of the estuary where salinity is generally above 

 15^f. Two such sites were selected for detailed 

 study. One is the mouth of Big Hole lagoon 

 that separates Sapelo Island Beach from Cabret- 

 ta Beach. The bottom is predominantly sand, 

 but ebb tide currents have eroded deposits of 

 hard clay that are derived from Pleistocene salt 

 marshes. The gobies occupy the small reefs in 

 sand and clay bottoms and often nest in isolated 

 hinged shells that are stabilized in the clay. The 

 second study site is a creek that runs under the 

 boat house of the University of Georgia Marine 

 Institute and that winds through the salt marsh. 

 This is a typical salt marsh creek with a mud 

 and shell bottom and mud banks that are bor- 

 dered with cord grass {Spartina alterniflora) . 

 Small reefs along the bank and bottom are ex- 

 posed when the approximately 2.1-m tide is low. 



Some specimens were obtained by seining at 

 Sapelo Island and other specimens by sampling 

 with a bucket dredge and otter trawl in the es- 

 tuary that ranges from the oligohaline Riceboro 

 Creek to Sapelo and St. Catherines Sounds. The 

 30-ft (9.1m) seine had 14-inch (6.35-mm) mesh. 

 The 20-ft (6 m) wide trawl had 1 14-inch (32- 

 mm) mesh. A June collection is from Chatham 

 County. Dip net collections were taken beneath 

 floating docks at Halfmoon Landing and Carrs 

 Neck Creek. Macroinvertebrates observed in 

 reefs were collected by hand or dip net. 



FISHERY BULLETIN: VOL. 71, NO. I 



HABITATS 



In the Sapelo Island region most collections 

 of G, bosci and G. ginsburgi were made in patches 

 of oyster shells or in isolated hinged shells. G. 

 bosci occurs where shells are not available in 

 Texas (Hoese, 1966) and in grassy areas in 

 Chesapeake Bay (Hildebrand and Schroeder, 

 1928). Some G. bosci were collected in marsh 

 pools, as they were by Kilby (1955), and some 

 among fouling communities (including sea 

 squirts, hydroids, barnacles, and small oysters) 

 on pilings, and on the underside of floating docks 

 in summer and winter, a habitat reported by 

 Joseph and Yerger (1956). 



Extensive trawling and dredging in a Georgia 

 estuary for 3 years produced four collections 

 of G. bosci at stations where water depth ranged 

 from approximately 4.5 to 12.0 m. Two were 

 from part of the lower estuary where shells are 

 abundant on the bottom, and two were from the 

 middle part of the estuary where the bottom 

 has various amounts of sand, gravel, mud, and 

 debris. A few were seined in sandy areas along 

 Sapelo Beach where cover was scarce. On 4 

 March 1969, 9 G. bosci were found along with 

 114 G. ginsburgi and 7 Hypsoblennius hentzi in 

 tubular burrows in an eroding clay outcrop on 

 Sapelo Beach. Burrows such as these, appar- 

 ently made by false angel wings (Petricola phol- 

 adiformis) , may be overwintering sites for large 

 portions of the goby populations. Gobies and 

 other fishes become scarce on the reefs in fall 

 and winter. Some G. bosci were found in mud 

 and debris at the edge of oyster reefs at near- 

 freezing water temperatures (Hoese) .' At tem- 

 peratures below 20°C many G. bosci were found 

 in mud-bottom marsh pools, where they appar- 

 ently burrow in the mud during the coldest part 

 of the winter, as speculated by Hildebrand and 

 Cable (1938). A mass migration of G. bosci 

 to deeper waters of the sounds in the winter is 

 unlikely, as they were trawled in shallows (gen- 

 erally less than 1.2 m) throughout the year 

 (Dawson, 1966). 



' Hoese, H. D. Studies on fishes associated with Amer- 

 ican oysters (Crassostrea virginica) . Unpublished man- 

 uscript filed at University of Southwestern Louisiana. 



280 



