Eels have been somewhat of an enigma to researchers, however, they have provided a vital fishery for Indigenous Australians for millennia. Aboriginal people in the coastal Darlots Creek system in VIC harvested and farmed Short-finned eels via complex systems of stone-walled trap and channels and ponds.
Freshwater eels are a part of the family Anguillidae contains a single genus, Anguilla. There are four species known from Australia with two inhabiting the Murray-Darling Basin (MBD), the Short-finned eel (Anguilla australis) and the Long-finned eel (Anguilla reinhardtii).
Short-finned eels are found in both Australia and New Zealand however, DNA analysis found genetic variations suggesting that different subspecies occur in each country. Short-finned eels typically exist in a variety of habitats including rivers, lakes, and swamps, generally with low or no flow.
Potential threats to freshwater eels include:
- Barriers to downstream migration of adults, particularly hydroelectricity schemes and associated turbines are cause for concern.
- Coastal wetland drainage and conversion may also be threats.
- Changes to oceanic currents associated with climate change will also affect larval dispersal.
The spawning patterns of eels have been a mystery for quite some time. It is now known that migrates to the sea to spawn, but exactly where spawning takes place is still unknown. It is currently believed that the spawning occurs in the Coral Sea between Fiji and Samoa. Short-finned eels spawn during November to March, with Long-finned eels being less confined seasonally with year-round spawning.
The larval eels are washed down the east Australian coast by the East Australian Current. As the leaf-like larvae (leptocephali) approach the continental shelf they grow into the traditional eel shape (glass eels) and the unpigmented glass eels enter fresh water in spring–summer and then transform into pigmented young eels. The short-finned eel larvae take about 7-9 months to migrate from the spawning grounds to the Australian east coast and are from 170-250 days old when they enter freshwaters. Long-finned eel juveniles leave marine waters to enter freshwater environments at a younger age than Short-finned eel, suggesting that the spawning grounds may be slightly closer to Australia (around Fiji) than Short-finned eels.
The glass eels and young eels then migrate upstream to the upper reaches of rivers, where they may remain for 20 years or more before a return migration to their marine spawning grounds to breed and then die. Movement from the estuary into the sea is influenced primarily by moon phase and water temperature, with this movement occurring in late summer – early autumn.
All of this awesome freshwater eel info (and more!) can be found in Mark Linterman’s new book, Fishes of the MDB
Featured image: Long-Finned Eel.
Source: Gunther Schmida
