The yellowfin tuna (Thunnus albacares) is a widely distributed, migratory species that supports valuable commercial fisheries throughout their range.
Management of migratory species requires knowledge of movement, mixing and key life history parameters such as growth rate, natural and fisheries mortality. Current management is based on the assumptions that the species is highly migratory and populations are well mixed, but these assumptions have been questioned by recent studies.
Since November 2015, yellowfin tuna have been tagged with conventional, archival and pop-up satellite tags (PSAT) in the South Atlantic Ocean around St Helena, with the goal of better understanding their movement patterns and ecology in this region.
Conventional tags were attached to 4049 yellowfin tuna (size range 24–158 cm fork length, FL), PSAT tags were deployed on 15 yellowfin in inshore St Helena waters (size range 95–138 cm FL) and 7 yellowfin (size range 125–140 cm FL) at Cardno Seamount, and archival tags were deployed on 48 yellowfin tuna in inshore St Helena waters (size range 69–111 cm FL).
Most yellowfin tuna remained within 70 km of their release location, suggesting a degree of retention to the region. Although displacement of yellowfin was generally low, the furthest distance travelled between release and recapture location was 2755 km, with other tuna also displaying large-scale movements.
Tagging revealed connections between inshore regions and seamounts, as well as links between St Helena waters and key fishing regions and putative spawning grounds in the Gulf of Guinea.
Serena Wright is a fisheries scientist from Cefas with an interest in fish behaviour, physiology and fisheries management. She started out as a fish physiologist looking at the energy use of fish using accelerometer tags. Since then, her work has focused on the use of models to track fish and assess how they change their behaviour in space and time. Recent research has mostly focused on tuna in the waters of St Helena.
Rhys Hobbs is the Marine and Fisheries Conservation Manager for the St Helena Government. He has worked for over 15 years in environmental regulation and he and his team are responsible for the monitoring and management of St Helena’s IUCN Category VI Marine Protected Area. Designated in 2016 this MPA is underpinned by a marine management plan that aims to sustainably manage St Helena’s marine environment, identifying pressures and threats, managing them where possible. Management strategies employed by Rhys and his team cover the fishery, tourism and recreational activities, scientific research as well as boundaries and zoning.