Armstrong: Distribution and abundance of Pleuronectes putnami and Pleuronectes americanus 
417 
was a sudden decrease in salinity in September 
caused by dilution from the heavy rains with Hurri- 
cane Bob in late August of that year. Sites compris- 
ing the depth gradient had similar patterns of salin- 
ity in all years of the study. 
Salinity gradient 
Both species were unevenly distributed along the 
salinity gradient, and their distributions changed 
seasonally (Table 2). The timing of peak abundance 
of smooth flounder at site 1 varied from year to year. 
In 1989 and 1990 smooth flounder were abundant in 
mid to late summer (Fig. 4). The influx of smooth 
flounder was associated with seasonal changes in the 
salinity regime from fresh to oligohaline (Fig. 2). In 
1991, smooth flounder were present at site 1 in all 
months sampled. In this year, salinity was higher 
than that during the two previous years (Fig. 2). 
Length frequencies of smooth flounder at site 1 (Fig. 
5) were significantly different (P<0.0001 in all 
monthly K-S tests, May-October) from those at site 
2 (Fig. 6), although the difference appears to 
be less in the autumn than in the spring. 
Larger fish (>100 mm) made up a higher pro- 
portion of the catch at site 1 in comparison with 
site 2, indicating differential migration among 
size classes. Winter flounder were rarely col- 
lected at site 1 (Fig. 7). They were found there 
only on a few occasions in September and Oc- 
tober when salinity was at a seasonal high. 
Smooth flounder were abundant at site 2 
during all months, and their average abun- 
dance at this site exceeded that of all other 
sites. Their abundance was generally high in 
the spring, lower in late summer to early au- 
tumn, and high again in mid to late autumn 
(Fig. 4). This trend was opposite to that ob- 
served for site 1. Correlation analysis of 
catches of smooth flounder at sites 1 and 2 in- 
dicated a weak but significant negative rela- 
tionship (P=0.032, r=-0.48). When catches 
were large at site 1, they tended to be small at 
site 2. This finding suggests that the same 
population of smooth flounder was migrating 
between the stations, although the length fre- 
quencies show that a greater proportion of 
larger smooth flounder than smaller smooth 
flounder travel the 3 km between the sites. 
Winter flounder were abundant at site 2 only 
during autumn (Fig. 7), although even during 
these periods of abundance, the catches of win- 
ter flounder were always lower than those for 
smooth flounder. The movement of winter 
flounder into site 2 from Great Bay proper was 
associated with relatively high salinities (Fig. 
2) and with low abundances of smooth floun- 
der (Fig. 4). The length frequencies of winter 
flounder collected from site 2 (Fig. 6) and site 
3 (Fig. 8) were similar. 
Smooth flounder occurred at site 3 in rela- 
tive abundance only in April, May, and June 
(Fig. 4). Catches of smooth flounder decreased 
significantly after June in all years. Winter 
flounder were most abundant at this site than 
at the other two sites comprising the salinity 
Apr May Jun Jul Aug Sop Oct Nov 
Apr May Jun Jul Aug Sep Oct Nov 
Month 
Figure 2 
Salinity at three sites sampled along a salinity gradient in Great 
Bay Estuary, New Hampshire. Mean salinity was highest at site 3 
(20.3 ppt) followed by site 2 (10.9 ppt) and then site 1 (4.2 ppt). 
Solid line = 1989; dotted line = 1990; dashed line = 1991. 
