Abstract Harald Dannevig was Australia’s first Director of fisheries research and Director of Australia’s first ocean-going research vessel. Dannevig’s initial contributions concerned hatchery technology, freshwater fisheries, and impacts of estuarine prawn trawling. Later, he revealed the growth and migration of sea mullet, the spawning of pelagic eggs in the coastal ocean, and he was the first to demonstrate the effect of onshore winds on recruitment to estuarine fisheries. Using plans of the first Norwegian research trawler Michael Sars, he advised on the construction and commissioning of Endeavour. He organized 99 research voyages over 6 years to determine suitable trawling grounds over ∼7000 km, discovering 263 new species, including 96 new fish species and ∼5000 catalogued specimens. Harald Dannevig’s significant achievements in Australia were soon forgotten after his death with the loss of Endeavour in the Southern Ocean at the beginning of World War I. Both Johan Hjort and Dannevig were numerate, loved natural history, and were keenly observant on the deck. As these two scientists did not correspond, their innovative and parallel thinking stems from the shared university environment with G.O. Sars, and the rapport between Sars and Harald’s father Gunder Dannevig, concerning the fish hatchery and stocking of larval cod.