A 15‐Year Time Series Shows Major Declines in Whale Sharks in Southern Mozambique

Auditore, Lisa‐Marie, Pierce, Simon J., Prebble, Clare E. M., Flam, Anna, Marshall, Andrea D., Venables, Stephanie K., Watts, Alexandra, Reeve‐Arnold, Katie E., Domenico, Genaye, Keeping, Jennifer, Méndez‐Jiménez, Adriana, Riensema, Alina, Rosero, Marcela, Cumbana, Lelia, Tilley, Alexander, Westling, Anna, Williams, Chris and Rohner, Christoph A. (2025) A 15‐Year Time Series Shows Major Declines in Whale Sharks in Southern Mozambique. Aquatic Conservation: Marine and Freshwater Ecosystems, 35 (10). e70224. ISSN 1099-0755

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Abstract

A 15‐year dataset (2005–2019) of 706 photo‐identified whale sharks (Rhincodon typus) off Praia do Tofo in Mozambique allowed us to assess the local abundance trend, and size‐ and sex‐specific sighting and abundance trends, using both generalised additive models and capture–mark–recapture models. Overall sightings per day were partially explained by temporal (year, day of year) and biophysical (sea surface temperature, time from high tide, moon illumination, Indian Ocean dipole index) predictors. There were no differences in environmental drivers between females, which comprised 26% of the study population, and males (74%). Similarly, demographic parameters (recapture probability, apparent survival, and probability of entry into the population) estimated in multi‐state open robust design capture–mark–recapture models showed no differences between sexes. Generalised additive models and multi‐state open robust design models showed a steep decline in whale shark sightings (−87%) and abundance (−89%), respectively. Female abundance was lower and decreased more sharply (−92%) than that of males (−81%), while the abundance of larger ≥ 7‐m individuals declined more (−99%) than medium‐sized (5–6.9 m, −87%) and small (≤ 5 m, −68%) sharks. This pronounced decline in one of the largest global aggregations of whale sharks highlights the pressing need for ongoing work to understand movement drivers, mitigate threats and protect this Endangered species.