When is a ditch a stream, or a brook or a rivulet? The Friends of the Sandy Bay Rivulet have known the answer to this question for a decade and they were pleased to have it confirmed once again on a recent Sunday by a leading freshwater ecologist, Professor Peter Davies.
The rivulet that makes its way down from Mt Wellington to the Derwent at Sandy Bay might look like a ditch in its concrete-lined lower reaches but, despite two centuries of misuse during which time it was used as a sewer, it remains a vibrant watercourse, giving life and sustenance to the wider environment of Tasmania’s capital.
Prof Davies, of the School of Zoology at the Universityof Tasmania, led members of the Friends – who for 10 years have been endeavouring to return the Sandy Bay Rivulet towards a more natural state – on a walk along its lower reaches to explain its importance in the greater scheme of things.
The rivulet remains a vital breeding ground for fish and amphibians, and a home to myriad bird and mammal species, even in areas where it moves out of the mountain foothills and dissects suburbia. To prove this point Prof Davies brought along specialist equipment to trap fish, and he managed to find four of the five native fish found in the rivulet at three locations, one near the rivulet tunnel that burrows under the Southern Outlet in Dynnyrne.
He found the spotted mountain galaxias (Galaxias truttaceus) and the jollytail (Galaxias maculatus), before catching several very large short-finned eels (Anguilla australis), the latter biding their time in the rivulet’s pools and backwaters before migrating to the Coral Sea near New Caledonia. Closer to the coast, where the rivulet flows unimpeded into the Derwent near Quayle St in Sandy Bay, Prof Davies caught the ‘‘freshwater flathead’’ known as the sandy (Pseudaphritis urvillii). Brown trout (Salmo trutta), transported from England in the late 1800s and actively stocked throughout Tasmania, were not found on the day of our excursion, despite being known to be resident in the rivulet.
Prof Davies, who lives in Sandy Bay, has conducted research into life in waterways around Tasmania for many years. In the Sandy Bay Rivulet, among several other streams, his research group also designed and built baffles to help native fish swim through concrete culverts.
As Prof Davies explained it, the rivulets that enter the Derwent River are important breeding and feeding grounds for several species of native fish, and there is still evidence of the great whitebait runs of estuarine species that once gave Tasmania a whitebait canning industry before the Derwent was overfished.
Some estuarine species use the rivulets to spawn, and their young develop there before returning to the ocean. Conversely, the galaxias found in Hobart’s rivulets lay their eggs in reeds in the tidal zone, so their young can mature in Storm Baybefore returning to breed. To facilitate this process, the Friends have planted reeds near the rivulet outlet.
For me the wildlife corridor created by the Sandy Bay Rivulet is Hobart’s premier bird-watching spot – with more than 80 species recorded there – but I cannot view birds in isolation and am always prepared to look at the bigger picture. For this reason I joined the Friends of the Rivulet when the organisation started in the early 2000s but over the years I have always managed a wry smile when I have seen white-faced herons stalking the rivulet’s tidal zone, feasting on a meal of the galaxias supported by the Friends’ endeavours.