CubeSat constellation shines light on fisheries studies: A case study of fish mortality events

In March 2023, a massive fish mortality event occurred in the Lower Darling-Baaka River in the south-east of Australia, which led to extensive media coverage. Yet to date the information on this event is incomplete and the severity of the event has not been quantified. Here, using Planet SuperDove observations from the CubeSat constellation, we demonstrate how to detect and quantify dead fish in the aquatic environment. The 4-m resolution daily imagery revealed the start, evolution, and end of the event. In this river with an average width of ∼40 m, the maximum detected areal coverage of dead fish reached ∼88,209 m 2 , corresponding to an estimated 4.0–8.0 million dead fish on the peak day. The reflectance spectral shapes from the dead-fish pixels appear similar to those measured in the field from another event, and they also differ from many other floating materials. The same method was also applied to a fish mortality event in Tampa Bay (Florida, USA) due to a harmful algal bloom, with successful detection that matched field reports. Because of the near real-time availability of the high-resolution high-revisit data from the Planet CubeSat constellation, this proof-of-concept study suggests that, with the knowledge of lower-detection limit and spectral characteristics of dead fish, a monitoring system can be established for near-real-time response at least for places with historical fish mortality events, and more CubeSat constellations in the future may eventually lead to a system to detect fish schools in surface waters. • Demonstrated detection and quantification of dead fish using 4-m CubeSat image. • Reconstructed the temporal evolution of a major river fish mortality event. • Showed the feasibility of near-real-time ecological disaster monitoring.