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Crook D.A.,Charles Darwin University | Crook D.A.,Arthur Rylah Institute for Environmental Research | Macdonald J.I.,Arthur Rylah Institute for Environmental Research | Macdonald J.I.,University of Iceland | And 5 more authors.
Freshwater Biology | Year: 2014

Summary: Spawning migration by freshwater eels to their marine spawning grounds is widely considered to be direct and rapid; however, emerging evidence suggests that eel migratory behaviour is more complex than previously thought, with potential implications for eel conservation and management. Over a 5-year period, we tagged 97 yellow-phase short-finned eels Anguilla australis with acoustic transmitters in the freshwater reaches of a south-eastern Australian river to: (i) examine environmental correlates associated with seaward migration; (ii) test the hypothesis that migration is rapid and direct once initiated and (iii) assess individual variation in behaviour associated with seaward migration. Twenty-three of the tagged eels migrated from fresh water into the estuary, whilst the remainder stayed within fresh water. Movement was detected primarily at night and eels entered the estuary throughout the year, with an increase in frequency over summer and following high river flows. Time in the estuary ranged from 1 to 305 days (median: 77 days). Movement into the sea was influenced primarily by the lunar phase, and to a lesser degree by water temperature, and occurred from late summer to early autumn. The extended residence and complex movements of migrating eels in the estuary suggest that they are considerably more vulnerable to exploitation than would be predicted by the generalised eel migration model of direct movement out to sea. © 2014 John Wiley & Sons Ltd.

Crook D.A.,Arthur Rylah Institute for Environmental Research | Koster W.M.,Arthur Rylah Institute for Environmental Research | Macdonald J.I.,Arthur Rylah Institute for Environmental Research | Nicol S.J.,British Petroleum | And 6 more authors.
Marine and Freshwater Research | Year: 2010

Understanding migratory requirements is critical for the conservation of diadromous fishes. Tupong (Pseudaphritis urvillii) are diadromous fishes found in freshwater and estuarine regions of south-eastern Australia. Previous studies have hypothesised that mature female tupong undertake downstream spawning migrations from freshwater to the estuary or sea, with a compensatory return of juveniles, and possibly spent fish, back upstream. We applied acoustic telemetry to test this hypothesis. We tagged 55 female tupong in two river systems in VICtoria, Australia, and tracked movements for 4- to 6-month periods over 2 years. Thirty-one fish undertook rapid downstream migrations and then appeared to move through the estuary and out to sea between May and August in each year. Migration was associated with relatively high river discharges, and movement from the estuary to the sea tended to occur most frequently during intermediate moon phases. Low rates of movement between September and April suggested that tupong inhabited restricted home ranges outside of the spawning season. The apparently disparate migratory patterns of female (catadromous) and male (non-diadromous) tupong are rare amongst fishes globally. Differential exertion of a range of selective pressures may have resulted in the evolution of sexual differences in migratory modes in this species. © 2010 CSIRO.

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