Possible Darter sighting

I received an email from Eric Woehler (Chair of Birds Tasmania), with an attachment outlining a possible Darter sighting and a request from the observers for help.
The sighting occurred during a wildfowl count at Moulting Lagoon on Tasmania's Eastcoast, about a week ago, and the following is a precis of the event.
During a pre-count briefing it was emphasised that if any unusual birds were seen, to take notes and talk to the organiser about it (Stewart Blackhall) rather than just add it to the list. He mentioned that in the past a Darter was reported, but he was unable to confirm it. This caused some mirth among the seasoned birders, as a Darter would indeed be an unlikely sighting in Tasmania.
On a beautiful calm day, the 4 observers in question, Ron Nagorcka, Ross Monash, Louisa d'Arville and an unnamed parks field officer, headed out on the Sherbourne property in the north-western arm of Moulting Lagoon. During the count, made with the aid of a spotting scope, they counted many wildfowl, especially Black Swans, some Grey Teal, Crested Grebes and cormorant. While doing a count of the cormorant numbers, Louisa excitedly noted a much larger cormorant among the Little Pied and Little Black Cormorants, all grouped together on an old, dilapidated hide. When this 'cormorant' turned its head, it showed off a long, slender, very straight, bright orange bill, with the orange seemingly stretching back behind its eyes. The bill was on the end of a long snakelike neck. After watching it for some time, noting its distinguishing features, they consulted the field guide. The longer tail, large body, long neck and sharp, unhooked bill, saw them all concluding that it was a Darter. Ross and Louisa have both lived in Queensland and seen Darters before, as has Ron.
They did manage to get some, in their words, "blurry photographs", by digiscoping with a camera that was about to run out of battery life! While not ruling out that it could have been a Great Cormorant, the 4 agreed that the bill was different to any cormorant, lacking the hooked end, but the all black bird lacked any white markings on its face, neck or wings, often seen in Darters.
The following day a number of observers went in search of the "darter", without success.
From the above, the 4 birders are requesting your assistance if you're heading for Moulting Lagoon. If you wish to go to the Sherbourne property, which is private land, or you would like more details on how to get there and how to get permission to go on to this property, you may contact Stewart Blackhall on 62336585 or Louisa d'Arville on 62238905.
[NB I am aware of only one other Darter record (but there may be more), sighted at Brumby's Creek, near Poatina, in July and August of 1980. My apologies if, in precising the information that I received, I have omitted or misrepresented any detail of this sighting.]