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Fishery Bulletin 96( 1 ), 1998 
inhabits deeper waters than the others (Table 10), 
spanning an overall bathymetric range from 7 to 110 
m, but is captured most frequently in waters deeper 
than 20 m (83% collected deeper than 20 m). 
Symphurus oculellus, including juveniles as small 
as 76 mm SL, have been collected in neritic waters 
deeper than 7 m, and none have been collected from 
estuarine habitats contrary to the capture depths of 
S. plagusia and S. tessellatus. However, estuarine 
environments in the geographic range of S. oculellus 
along northeastern South America have not been as 
thoroughly sampled as have the nearshore habitats 
occupied by S. plagusia and juvenile S. tessellatus in 
the northern Caribbean and southern Brazilian ar- 
eas. Symphurus civitatium, the northernmost-occur- 
ring species in this group, is the only Atlantic spe- 
cies with a distribution that is allopatric in compari- 
son with that of other members of this species group. 
Depth distribution and substrate requirements of 
this species were discussed above. 
The majority of the S. jenynsi population is allo- 
patric in comparison with populations of other 
tonguefishes. This species lives on mud bottoms on 
the inner continental shelf in the South Atlantic. The 
bathymetric distribution spans depths ranging from 
about 17 m to 190 m (Menezes and Benvegnu, 1976), 
but most specimens have been collected between 12 
and 25 m. In this region, S. jenynsi is sometimes col- 
lected with juvenile S. tessellatus. 
Factors influencing ecological distributions ob- 
served for western Atlantic tonguefishes are rather 
complex. On a geographic scale, the species’ range 
corresponds mostly with the limits of previously iden- 
tified faunal regions. The ecological, or local, distri- 
bution of a species is reflected in the spatial and 
bathymetric distribution of particular substrates 
(Topp and Hoff, 1972) within the broader geographic 
range. Association of most flatfishes with sediments 
rather than hard substrata indicates that the struc- 
ture of the sea bed is an important factor controlling 
their distribution (Gibson, 1994, and references 
therein). Topp and Hoff (1972) suggested that strong 
interrelationships between apparent substrate re- 
quirements of individual species of flatfish could pos- 
sibly explain patterns of geographical and bathymet- 
ric distributions observed for these fishes. Other stud- 
ies (Pearcy, 1978) cautioned that direct examination 
only of substrate types without examination of depth 
of occurrence may be incomplete because influences 
of depth and sediments on the distribution of benthic 
organisms are usually closely correlated and are dif- 
ficult to separate. Sediment texture generally de- 
creases with increasing depth of water, with small 
particles usually transported from regions of high 
energy waves and currents into deep, low-energy sedi- 
mentary environments, and coarse sediments, such 
as sands, generally are deposited in shallow water 
close to their continental source. According to 
Thorson (1957), physical and chemical compositions 
of sediments may be the main factor in determining 
the general patterns of distributions of infaunal and 
epifaunal invertebrates on the level sea floor. Fau- 
nal changes in both benthic invertebrates and verte- 
brates on the continental shelf and slope have also 
been thought to result from depth-related changes 
in physicochemical properties (Sanders and Hessler 
1969; Haedrich et al., 1975). However, the emerging 
paradigm is that the relations between organism dis- 
tributions and the dynamic sedimentary and hydro- 
dynamic environment are complex (Snelgrove and 
Butman, 1994), especially when considering that 
grain size covaries with other factors including sedi- 
mentary organic matter content, pore-water chem- 
istry, and microbial abundance and composition, all 
of which are influenced by near-bed flow regime. 
Ecological distributional patterns observed for 
western Atlantic tonguefishes may result directly 
through an active process in which tonguefishes se- 
lect particular substrates based on physical charac- 
teristics of the substrate (i.e. particle size and com- 
position of the sediments, ease of burying, coloration 
of the sediments). Conversely, tonguefishes may in- 
directly occupy particular substrates because the 
suite of physicochemical characteristics (temperature 
regime, current strength, water depth, salinity, oxy- 
gen concentration, ambient light levels, etc.) required 
by that species may occur coincident with deposi- 
tional environments for particular sediment types. 
Reichert and Van der Veer (1991) provided descrip- 
tive information regarding substrate preference of 
settling S. plagiusa juveniles, but no experimental 
work on substrate selection or preference has been 
done for any species of western Atlantic tonguefish, 
and hypotheses concerning active selection of sub- 
strates by tonguefishes remain untested. 
Yet another factor potentially contributing to sub- 
strate selection, and indirectly to the ecological dis- 
tributional patterns observed for tonguefishes, may 
be related to substrate selection by biotic associates 
of tonguefishes. Diet studies (Mahadeva, 1956; Aus- 
tin and Austin, 1971; Topp and Hoff, 1972; Stickney, 
1976; Kawakami, 1976; MacPherson, 1978; Toepfer 
and Fleeger, 1995) indicate strong preferences by 
symphurine tonguefishes for small epibenthic and 
infaunal invertebrates as food sources. Morphologi- 
cal characteristics of tonguefishes, such as the rela- 
tively small size of the mouth and reduced or absent 
dentition on ocular-side jaws in many shallow-water 
species, may also reflect adaptations (or constraints) 
for specialized feeding that would determine the size 
