Fishing and loss of connectivity interact to threaten persistence of a migratory population in Australia

Migratory animals depend on connected habitats and appropriate migratory cues to complete their life-cycles. Diadromous fish exemplify the migratory life-cycles by moving between connected fresh and saltwater habitats.... [ view full abstract ]

Migratory animals depend on connected habitats and appropriate migratory cues to complete their life-cycles. Diadromous fish exemplify the migratory life-cycles by moving between connected fresh and saltwater habitats. Migration increases exposure of diadromous fish to disturbances and it is critical that managers incorporate impacts to populations and connections between habitats into species management. However, how the interaction between direct impacts like fishing pressure and connectivity loss like river flow modification affect population has seldom been addressed. Here, we assess alternative management actions for diadromous fish by developing a spatio-temporal population model informed by animal telemetry data to simulate population dynamics under multiple disturbances to the life cycle of Australian Bass (Percalates novemaculeata), a diadromous fish. Results indicated that the benefits of seasonal closure depended on the interactions between how fishing pressure was limited (catch or fishing effort), the response of anglers to fishery regulations and river flow regimes. Seasonal closures could be ineffective if displacement of fishing pressure occurred. In addition, shifting from spawning ground closure to feeding ground might maintain higher population abundances in low flow event under fishing effort control while the effectiveness among different seasonal closure schemes stayed relatively stable with limited catch amount. This highlights a need for flexible management strategies that respond to variation in river flow regimes and the responses of anglers to efforts that limit their activities in certain locations. Efficient management planning depends on understanding the dynamic distributions of both the fish population and human disturbances.