Gaughan and Potter: Analysis of diet and feeding strategies within an assemblage of estuarine larval fish 
729 
ping (18.6% and 20.9%) were greater than those ob- 
tained by accounting for zooplankton abundance data 
(11.6% and 13.9%, Table 4). 
Relation between zooplankton abundance 
and both feeding prevalence and mean DNO 
Zooplankton abundance at sites within months was 
not significantly related to either feeding prevalence 
(P>0.05, r=0.346, n= 26) or mean DNO (P>0.1, 
r=0.146, n=15) of fish larvae within the correspond- 
ing samples. 
Discussion 
Numbers of prey consumed and prey size 
Afurcagobius suppositus, because it ingested larger 
prey types, e.g. G. imparipes, consumed the least 
number of prey. The other species ate larger num- 
bers of small and intermediate-size prey, e.g. cope- 
pod nauplii and O. simplex. The significant increase 
in numbers of prey with length for U. carinirostris 
only was probably attributable to the fact that the 
magnitude of the range of length of individuals ex- 
amined for this species was 12 mm, whereas that of 
the other species was less than 6 mm. 
Despite marked increases in mouth width during 
the growth of each species except U. carinirostris, 
average prey width of the five species increased only 
slightly with growth. Although smaller larvae con- 
sumed prey almost as wide as their mouths, larger 
larvae typically ate prey far smaller than their mouth 
size. Furthermore, the smaller larvae of each spe- 
cies consumed some prey items almost as wide as 
those eaten by larvae in the larger size classes. These 
data indicate that mouth width was not limiting the 
ingestion of larger prey types among larvae in the 
larger size classes. 
The dominance of relatively small prey in the di- 
ets of larval fish in Wilson Inlet reflects the domi- 
nance of these types of zooplankton in the environ- 
ment. During the study period, copepod nauplii, O. 
simplex, calanoid copepodites and harpacticoids were 
33 times more abundant than the adults of G. 
imparipes and A. simplex collectively, the only com- 
mon large prey. Thus, as has previously been found 
for other larval fish (e.g. Ware and Lambert, 1985; 
Kellermann, 1990), prey availability strongly influ- 
enced the sizes of prey consumed. 
From an early age and size, Afurcagobius sup- 
positus ate larger prey than the other four species. 
Since this species hatches at a more advanced stage 
and with better developed fins than the other four 
species (Neira et al., in press), they were probably su- 
perior swimmers and thus more efficient at captur- 
ing larger prey. Greater mobility may have also re- 
sulted in A. suppositus searching a larger volume of 
water (Hunter, 1984), which would increase the rate at 
which the larger and less abundant zooplankton were 
encountered. The possession of a larger mouth ap- 
parently allows A. suppositus to take advantage of 
larger prey in presumably more frequent encounters. 
Mouth size and DNO 
Although A. suppositus had the largest mouth and 
consumed the largest and most diverse prey, the rela- 
tive differences in mouth size of the other four spe- 
cies were not accompanied by corresponding differ- 
ences in the size and composition of prey. A lack of a 
predictive relation between mouth size and diet has 
previously been recorded for fish larvae from another 
estuary (Laroche, 1982) and more recently for lar- 
vae of freshwater fish in an experimental situation 
(Bremigan and Stein, 1994). In Wilson Inlet, this situ- 
ation was further highlighted by the lack of a rela- 
tion between the prevalence of significant DNO and 
the mouth structure of the five species. Thus, the 
prevalence of significant DNO was not particularly 
high between P. olorum and F. lateralis (Table 4), the 
species with the most similar mouth structure, 
whereas P. olorum and U. carinirostris had very simi- 
lar diets, as indicated by the high prevalence of sig- 
nificant DNO (Table 4), but had different-size 
mouths. Conversely, the diet of A. suppositus over- 
lapped significantly only with that of U. carinirostris, 
the species with the smallest mouth. Parablennius 
tasmanianus and F. lateralis, the only other species- 
pair to exhibit more than one case of significant DNO, 
also had dissimilar mouths. Finally, A. suppositus 
and P tasmanianus had the largest mouths but the 
most divergent diets. 
Along with the general lack of a relation between 
mouth size and diet, the relatively frequent occur- 
rence (32.6%) of significant DNO amongst the larval 
fish in Wilson Inlet, when prey abundance was taken 
into account, was also attributable to the high con- 
centrations of relatively limited choices of acceptable 
prey types. The lack of a relation between concen- 
trations of zooplankton and both feeding prevalence 
and mean DNO within samples was also probably a 
result of consistently high concentrations of zooplank- 
ton. Consequently, significant DNO among larval fish 
in Wilson Inlet provided no evidence of competition 
for food. Furthermore, Gaughan and Potter (1995) 
found that abundances of zooplankton and larval fish 
were significantly correlated at only two of the four 
sampling regions in Wilson Inlet. The lack of a rela- 
