34 
J. D. KOEHN & W. G. O’CONNOR 
offshore from New Zealand supports the theory 
of McDowall (1978) that long-range dispersal of 
diadromous species may occur despite oceanic 
barriers. 
Recent influences 
The distribution of fish species recorded during 
surveys in other waterways has often been cor¬ 
related with the availability of suitable habitats 
(e.g. Cadwallader 1979, Jackson & Davies 1983, 
Koehn 1986a, 1986b, 1986c) and with access to 
those habitats. The wide distribution of the 
short-finned eel in the Otway region is indicati ve 
of the wide range of habitats which the species 
can tolerate (Cadwallader Sc Backhouse 1983) 
and of its ability to negotiate barriers. The com¬ 
mon galaxias, though less able to negotiate bar¬ 
riers, is also widespread and was found in a 
variety of habitats. Species with more specific 
habitat requirements such as freshwater black- 
fish and tupong, both of which prefer slower- 
flowing waters (Koehn 1986d, unpublished 
data), had more restricted distributions. Tupong 
appear to be particularly susceptible to stream 
barriers and were not found in the upper reaches 
of steep streams, although they are found well 
inland in larger rivers such as the Gellibrand 
(Tunbridge & Glenane 1983). During our survey 
tupong were not found above the “rapids” on 
the Erskine River nor above a road crossing on 
the Cumberland River consisting of pipes where 
uniform water velocities were particularly fast. 
Freshwater blackfish are common in the Gel¬ 
librand and Barwon river systems but were not 
found in Charleys and Lardners Creeks, tribu¬ 
taries of the Gellibrand River, despite the pres¬ 
ence of ample suitable habitat. Both these sites 
had been subjected to extremely heavy sedi¬ 
mentation, probably due to the establishment of 
surrounding pine plantations, and this may have 
contributed to the absence of freshwater black- 
fish. The eggs of freshwater blackfish die if they 
remain covered with silt (Koehn unpublished 
data). Moreover, because this species requires a 
clean surface on which to lay its adhesive eggs, 
spawning may not take place or may be unsuc¬ 
cessful if suitable sites are covered by a thick 
layer of sediment. 
Fish distributions in the Otway region pro¬ 
bably have not changed markedly in recent years 
as our results concur with those of Renowden 
(1968) and Baxter (1985), but a major change 
has occurred during the past century with the 
introduction of trout. Brown trout were par¬ 
ticularly abundant in the cool, well-oxygenated 
waters of the Otway coastal streams, which suit 
the habit of this species and contain gravel 
substrates which it requires for spawning 
(McDowall & Tilzey 1980). Apart from creating 
widespread populations of a new species, such 
introductions are likely to have affected the dis¬ 
tribution of native fish species. 
Published literature suggests that the broad- 
finned galaxias is usually found in fast-flowing 
water in the upper reaches of steep, rocky 
streams (Cadwallader Sc Backhouse 1983). Our 
results show that the species is also found in 
slow-flowing reaches of streams where the short- 
finned eel was the only other species present. 
The distribution of the broad-finned galaxias 
may be severely affected by the presence of other 
species, particularly brown trout (Jackson & 
Williams 1980) which at some sites appeared to 
restrict the broad-finned galaxias to shallow 
riffles not accessible to trout (Koehn unpub¬ 
lished data). Brown trout are voracious preda¬ 
tors and in many areas fish can form a large part 
of their diet. The effects of brown trout on the 
distribution of the mountain galaxias are more 
comprehensively documented, mutually exclu¬ 
sive populations of these two species being com¬ 
mon (Tilzey 1976, Cadwallader 1979, Fletcher 
1979, Jackson & Davies 1983). It has been sug¬ 
gested that brown trout may also be detrimental 
to Australian grayling, Prototroctes maraem 
(Jackson & Koehn 1988). 
The other three introduced species in the 
Otway coastal streams were neither abundant 
nor widespread, in contrast to the large numbers 
of six introduced species present in the Barwon 
and Gellibrand Rivers (Cadwallader & Back¬ 
house 1983, Hall & Tunbridge 1988, Tunbridge 
Sc Glenane 1988). Predation, particularly by 
trout and redfin, as well as competition for food 
and space by introduced species can be es¬ 
pecially detrimental to native fish populations 
(Cadwallader Sc Backhouse 1983). The introduc¬ 
tion of additional exotic species should therefore 
be avoided. 
CONSERVATION AND MANAGEMENT 
The Otway region, in particular the Otway 
Range, is considered to be an important conser¬ 
vation area where many streams have been given 
high conservation status (Tunbridge & Glenane 
1983, Macmillan et al. 1987). Although none of 
the fish species found in the region is considered 
endangered at present, several species are con- 
