Abstract
The Argo Basin, located in the eastern Indian Ocean off northwestern Australia, is the primary spawning ground for Southern Bluefin Tuna (Thunnus maccoyii). Understanding the environmental drivers of larval distribution in this region is essential to anticipate potential climate impacts. Using data from the BLOOFINZ cruise, we applied spatially explicit Bayesian models with Tweedie likelihoods to evaluate the influence of sea surface temperature, sea level anomaly, sea surface salinity, chlorophyll-a concentration, bathymetry, and seabed aspect on larval density (density standardized by filtered volume). The best-supported model revealed strong nonlinear responses to temperature, mesoscale activity, and depth. Larval density increased with warmer surface waters, peaked at intermediate depths, and was highest under moderate sea level anomalies, suggesting that retention and feeding conditions are maximized under these circumstances. Seabed aspect had a negative effect, consistent with topography-flow interactions that can reduce retention. The spatial component of the model identified a hotspot of larval density in the southern–southwestern basin and lower density toward the north, with lowest uncertainty in well-sampled central areas. Projections for 2050 under a mid-range climate scenario indicated a heterogeneous redistribution of suitable larval habitat, with declines in central and southeastern spawning areas and increases toward the northeast. These findings highlight the sensitivity of Southern Bluefin Tuna larvae to oceanographic conditions and climate change, and they emphasize the need for adaptive, climate-informed management of spawning habitats. | We deeply thank A. García, J. Lamkin and T. Gerard for opening and aligning our collaboration groups from Spain and USA. We sincerely thank A. Jivanjee and L. Mattison during the tuna larvae sampling and processing onboard, extend our gratitude to the crew of the R/V Roger Revelle for their assistance above and beyond during the RR2201 cruise. This study was funded by the INDITUN project PID2021/122862NB/100 UE-FEDER (R.L.-C.) and grant PRX23/00189 (R.L.-C.) supported by the Ministry of Science, Innovation and Universities (MICINN) of the Spanish government, U. S. National Science Foundation awards BLOOFINZ-IO OCE-1851558 (M.R.L.) and OCE-18513951 (E.M.), and contributes to the Second International Indian Ocean Expedition (IIOE-2 endorsed project EP046). Zooplankton and larval fish samples were collected under Australian Government permit AU-COM2021-520 and Australian Marine Parks permit PA2021-00062-2 issued by the Director of National Parks, Australia. Views expressed in this publication do not necessarily represent those of the Director of National Parks or theAustralian Government. R.L.-C. gratefully acknowledges financial support by the Fulbright Program, which is sponsored by the U.S. Department of State, the U.S. – Spain Fulbright Commission. | Peer reviewed