Monitoring fish populations using stereo-DOV-based surveys and open-access tools in the Gulf of California

Monitoring fish populations is essential to assess spatial and temporal changes, particularly in an era in which some species are experiencing a rapid decline. Among the great diversity of methodologies for this purpose, stereo-video systems have grown in popularity in the past few decades. However, despite their advantages for surveying fishes, funding for research and monitoring of marine systems is limited. In this context, we aimed to estimate fish relative abundance, species richness, and length-frequency distribution in a Marine Protected Area (MPA) integrating open-source software tools. We recorded fish species using a diver-operated stereo-video system (stereo-DOV) comprised of a pair of GoPro cameras. We conducted five surveys in El Bajo Espiritu Santo seamount (EBES; Gulf of California, Mexico) between September 2021 and October 2022. We registered 90,039 individuals belonging to 26 species, from which 942 fish individuals from 13 species were measured. Species richness remained about the same during the five surveys, whereas fish relative abundance was lower in March 2022. Species composition shifted throughout the year, with 11–13 species found through the year, and the rest found seasonally. The methods presented here offer a low-budget option for institutions to conduct fish monitoring programs.