Rapid physiological colouration change is a challenge - but not a hindrance - to successful photo identification of giant sunfish (Mola alexandrini, Molidae)

Photo ID is a common tool in ecology, but has not previously been attempted for the ocean sunfishes ( Mola spp., Molidae; ‘molids’). The technique, based on body patterns, could potentially be informative studying seasonal occurrence of giant sunfish alexandrini ) Bali reefs (Indonesia), where this species an important drawcard local SCUBA diving tourism. However, molids are capable rapid physiological colouration change, which may complicate application method. Our study aimed to determine if photo nevertheless achievable and informative. To test this, we created citizen-science platform ‘Match My Mola’ crowd-sourcing imagery (photos video) M. Bali, undertook trial matching (n=1,098 submissions). submitted revealed wide range pattern clarity, from fish with no bold displays. Video confirmed change can occur seconds low high contrast, cause individuals look very different between moments. individual patterns appear stable although at least some parts become inconspicuous during contrast Despite possible, including instances, only partial visible one image compared another. true negatives (confirming two same) challenging. Most identified matches were photographed by divers same day. Only small number (n=9) found resighting durations ≥1 day (1 – 2,652 days). These demonstrate that return both within seasons, duration 7.2 years constituting longest known example molid site fidelity. Comparing morphology resightings > 1 year (n=6) limited indications growth, contradicting current understanding growth captive mola ), highlighting knowledge gap regarding wild. Continued area provide valuable complementary information future studies using other methods as well further insights into