The untapped potential of transit echosounders for monitoring global pelagic fauna

Ship echosounders are essential tools for observing the distribution of organisms within the water column. They enable the study of deep pelagic fauna, likely the most extensive and abundant animal community in the global ocean, yet also one of the least studied. Until now, observations have been constrained by costly and clearly insufficient fishing efforts in one of the most vast and challenging ecosystems in the planet. This situation can now be alleviated through the use of sonar observations. Every day, national research fleets worldwide cover thousands of kilometers, equipped with the most advanced, calibrated, multi-frequency sonars available. Transit routes between scientific missions cover extensive ocean areas, crossing biogeographic provinces, current systems, and eddies. However, sonars are rarely turned on, and even when they are, the data is seldom accessible. This represents a monumental deployment of observational instruments, with daily vessel operation costs ranging from 20,000 to 50,000 euros, which is currently being underutilized. The reasons for this are varied, including jurisdictional issues in foreign national waters and a lack of resources to adequately operate sonars, centralize, process, and make data available. In this communication, we show the current gaps in the spatial and temporal distribution of sonar observations on a global scale. We also estimate how many observations we would have today if national research fleets had recorded and shared transit data over the past 10 years. In addition, we will present potential solutions, as the recent initiative submitted to the French Oceanographic Fleet to collect and deliver transit sonar data to the scientific community, as well as the international initiative GAIN, aimed at developing the first global sonar database updated on a regular basis. Most importantly, this communication seeks to foster dialogue among scientists, policymakers, and legal experts attending the One Ocean Science Congress and the Third United Nations Conference on the Oceans, with the goal of finding solutions to this international challenge.