Emigration mediates fishing mortality on spawning females in an estuarine crab fishery

Context Movement and migration are important components of population dynamics and affect the susceptibility of different population units to fishing mortality. Aims We applied acoustic telemetry to investigate emigration from heavily fished estuarine habitats to lightly fished inshore habitats in the largest blue swimmer crab (Portunus armatus) fishery in south-eastern Australia (Wallis Lake, New South Wales). Methods Eighty recently moulted mature female crabs were tagged across four tagging cohorts (November 2023, January, February and March 2024) and two sizes (pre-recruited, 60–65-mm carapace length, CL; recruited, ≥65 mm CL), and their movements tracked on an array of estuarine and inshore receivers. Key results Over 60% of tagged crabs left the estuary, but emigration rates were higher for pre-recruited sizes. Modelling indicated a minor influence of reduced water temperature and conductivity on emigration probability for recruited crabs, and movements showed some synchronisation with larger tides. Conclusions Mature female crabs emigrate from the estuary over the warmer months, and are likely to spawn in inshore waters. Implications It is likely that emigration has implications for both spawning and fisheries productivity, but resolution of early life-history connectivity patterns is critical for defining the full implications of these newly resolved stock dynamics.