First tracking of the oceanic spawning migrations of Australasian short-finned eels (Anguilla australis)

Anguillid eel populations have declined dramatically over the last 50 years in many regions of the world, and numerous species are now under threat. A critical life-history phase is migration from freshwater to distant oceans, culminating in a single life-time spawning event. For many anguillids, especially those in the southern hemisphere, mystery still shrouds their oceanic spawning migrations. We investigated the oceanic spawning migrations of the Australasian short-finned eel (Anguilla australis) using pop-up satellite archival tags. Eels were collected from river estuaries (38 degrees 5,142 degrees E) in south-eastern temperate Australia. In 2019,16 eels were tracked for up to about 5 months, similar to 2620 km from release, and as far north as the tropical Coral Sea (22 degrees 5,155 degrees E) off the north-east coast of Australia. Eels from southern Australia appeared to access deep water off the Australian coast via two main routes: (i) directly east via Bass Strait, or (ii) south-east around Tasmania, which is the shortest route to deep water. Tagged eels exhibited strong diel vertical migrations, alternating between the warm euphotic zone (similar to 100-300 m, 15-20 degrees C) at night and the mesopelagic zone (similar to 700-900 m, 6-8 degrees C) during the day. Marine predators, probably lamnid sharks, tuna, or marine mammals, ended many eel migrations (at least similar to 30%), largely before the eels had left the Australian continental shelf. The long and risky marine migrations of Australasian eels highlight the need for better information on the processes contributing to eel mortality throughout the life cycle, including the impacts of future changes to oceanic currents, predator abundance and direct anthropogenic disturbances.

Automated summary

Anguillid eel populations have declined dramatically over the past 50 years in many regions, with numerous species now facing extinction. Research on the oceanic spawning migrations of the Australasian short-finned eel revealed that they mainly access deep waters off the Australian coast through two main routes: directly east via Bass Strait, or southeast around Tasmania, which is the shortest route.