Trends and drivers of French tropical tuna purse-seine vessel behavior in the Atlantic and Indian Oceans, 2004–2020

Abstract

This study examines the spatio-temporal trends in fishing practices at the fishing trip scale of the French tropical tuna purse-seine fleet in the Indian and Atlantic Oceans on 17 years, focusing on trends in fishing on free-swimming schools (FSC) versus fishing on floating objects (FOBs). Key metrics, such as trip duration, median speed, sinuosity, area explored and the fraction of sets of FOBs, were calculated to quantify fishing trip patterns, and a PCA analysis was conducted to explore relationships between these metrics. Our findings show a marked shift towards FOB fishing, likely driven by advancements in tracking technology, which have improved fishing efficiency and reduced search time, and changes in regulations and fishing context, which have provided unintentional incentives for FOB fishing. The data reveal distinct trends between oceans, with shorter fishing trips and a higher rate of FOB fishing in the Indian Ocean, likely linked to recent increases in skipjack tuna abundance and catch limits on yellowfin tuna in that ocean. Temporal changes in fishing trip metrics suggest that the key factors influencing fishing strategies include oceanographic variability, management regulations, and socio-economic conditions like piracy and fuel costs. Our analysis provides critical insights into how technological innovations and environmental factors shape fishing strategies, contributing to the sustainable management of tuna fisheries.