420 
Fishery Bulletin 95(3), 1 997 
study, that the center of greatest abundance for 
smooth flounder is in the mesohaline part of the es- 
tuary, is in agreement with these previous studies. 
Site 3 was the site of greatest abundance for win- 
ter flounder. Movements into site 2 were seen in late 
summer or early autumn in all years. Little infor- 
mation is available concerning the response of juve- 
nile winter flounder to salinity gradients. Most stud- 
ies on the distribution of winter flounder have con- 
sidered only temperature or light as important abi- 
otic factors that influence seasonal or short-term 
movements (McCracken, 1963; Oviatt and Nixon, 
1973, Casterlin and Reynolds, 1982). Pearcy (1962) 
found a relatively homogeneous distribution of 
age-1 winter flounder throughout a salinity gradi- 
ent in Mystic River Estuary, Connecticut, that was 
maintained through all seasons. However, his low- 
est salinity station was higher in salinity than both 
site 1 and site 2; therefore he did not 
sample habitats that might be only sea- 
sonably available. Pearcy (1962) also 
documented movement of young-of-the- 
year winter flounder from the lower es- 
tuary to the upper estuary during the 
summer months. Indirect evidence for 
similar movement by young-of-the-year 
winter flounder in Great Bay Estuary is 
presented here. No young-of-the-year win- 
ter flounder were caught in upper Great 
Bay until late summer and early autumn 
(Figs. 8 and 11), indicating an influx from 
the lower estuary. The lack of small win- 
ter flounder during the early part of the 
year was not an artifact of gear selectiv- 
ity because young-of-the-year smooth 
flounder as small as 25 mm TL were 
caught, indicating that small young-of- 
the-year winter flounder would have been 
caught also if they had been present. 
Winter flounder spawn in the middle and 
lower portions of Great Bay Estuary and 
adjacent to the estuary in shallow coastal 
waters. Young-of-the-year winter flounder 
show little movement for a few months 
after metamorphosis (Saucerman, 1991); 
therefore it is not until they reach a larger 
size (30-50 mm TL) that they begin to 
move into the upper estuary. 
Salinity is considered one of the most 
important factors affecting habitat use 
by estuarine fishes. The distributions 
and movements of several flatfish spe- 
cies including Solea solea (Coggan and 
Dando, 1988; Dorel et al., 1991), Pleuro- 
nectes platessa (Poxton and Nasir, 1985), 
and Platichthys flesus (Riley et al., 1981; 
Kerstan, 1991) have been correlated 
with salinity. A natural estuarine salin- 
ity gradient, in which habitats are cat- 
egorized from benign to harsh in rela- 
tion to tolerance by species, may serve 
as part of a continuum of physiological 
stress (Peterson and Ross, 1991). Spe- 
cies seeking to maximize growth must 
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Figure 4 
Mean number of smooth flounder, Pleuronectes putnami, caught per ten 
minute tow at three sites along a salinity gradient in Great Bay Estuary, 
New Hampshire, May 1989-September 1991. Site 1 = oligohaline; site 2 = 
mesohaline; site 3 = polyhaline. Error bars are one standard error of the 
mean. 
