Daniel C. Gledhill (1), Alistair J. Hobday (2), Matthew Lansdell (3), David Welch (4), Stephen Sutton (5), Adrian Jeloudev (6), Matt Koopman (7), Adam Smith (8), Scott Cooper (9) and Peter Last (10)

1 CSIRO Oceans and Atmosphere, GPO Box 1538, Hobart, Tasmania 7001, Australia

2 CSIRO Oceans and Atmosphere, GPO Box 1538, Hobart, Tasmania 7001, Australia

3 CSIRO Oceans and Atmosphere, GPO Box 1538, Hobart, Tasmania 7001, Australia

4 C2O Fisheries, PO Box 3041, Cairns, Qld 4870, Australia, and the Australian Underwater Federation

National Spearfishing Commission, 14 Cleveland Terrace, Townsville, Qld 4810, Australia

5 Atlantic Salmon Federation, PO Box 5200, St. Andrews, NB, E5B 3S8 CAN

6 Underwater Skindivers & Fishermen’s Association, PO Box 362, Brookvale, NSW 2100, Australia.

7 Southern Freedivers, PO Box 213, Brunswick, Vic. 3056, Australia

8 Australian Underwater Federation National Spearfishing Commission, 14 Cleveland Terrace, Townsville, Qld 4810, Australia

9 CSIRO Oceans and Atmosphere, GPO Box 1538, Hobart, Tasmania 7001, Australia

10 CSIRO Oceans and Atmosphere, GPO Box 1538, Hobart, Tasmania 7001, Australia

Biological change in coastal marine waters resulting from global warming is now well documented. While Eastern Australian waters are recognised as a warming hotspot, measuring and interpreting multi-decadal, climate induced impact from poorly defined baselines remains challenging. A paucity of high quality time- series  data  is  limiting  research  efforts  to  interpret change  in the  region.  One  of  few  temporally  and geographically extensive, high quality datasets from the region have been compiled during spearfishing competitions held since the 1960s in New South Wales and Victoria. Standardised recording practices along with competitive participants have contributed to quality and consistency in identifications and recording. From  these  data,  evidence  is  found  for  change  in  fish  communities,  along  with  changes  in  species occurrence, range and capture frequency that are consistent with climate change impacts. Challenges were encountered in attributing change directly to climate-change impact, and in determining historic species- range margins in dynamic, data poor waters. We also recognise challenges and benefits in utilising a non- traditional data source, and have gained lessons from engaging with a passionate community group. Understanding changes in fishing practice could not have been achieved without close engagement with data-collectors, and failure to do so could contribute to under-or over-reporting impacts in application of similar citizen-science data.