Spawning behaviours of the fisheries significant Tarwhine (Rhabdosargus sarba) have been hypothesised from assessments of their reproductive development, and ex-situ aquaculture research, indicating competitive group-spawning behaviours for the species. This study supports these previous findings with video of a Tarwhine aggregation event (estimated 50+ individuals) on the 25th of February 2026, in the Fly Point Marine Protected Area (NSW Australia). Captured with handheld cinema camera on SCUBA at 18m, two rapid vertical rushes were recorded; characteristic behaviour of group-spawning, demersal marine fishes. Gamete release was not recorded but was likely obscured by the rapid ascent of participating fish. Arcing shoaling behaviours were also observed and may indicate participating spawners anticipating potential vertical rushes. Environmental metadata also points toward this being spawning behaviour, with the event coinciding with the swap to an outgoing tide, and the shoal depth providing enough headroom for vertical rushes, whilst potentially minimising barotrauma injuries from rapid ascents. These findings, which occurred outside the peak reproductive period for Tarwhine in this region, within a no-take sanctuary zone, have implications for the species and its fisheries management. Further efforts should aim to characterise the spawning behaviours of Tarwhine and other commercially significant demersal fishes, with in-situ observations.