Abstract
The Philippines is home to the second largest known population of whale sharks in the world. The species is listed as endangered due to continued population declines in the Indo-Pacific. Knowledge about the connectivity within Southeast Asia remains poor, and thus international management is difficult. Here, we employed pop-up archival tags, data mining and dedicated effort to understand an aggregation of whale sharks at Honda Bay, Palawan, Philippines, and its role in the species' conservation. Between Apr and Oct 2018, we conducted 159 surveys identifying 117 individual whale sharks through their unique spot patterns (96.5% male, mean 4.5 m). A further 66 individual whale sharks were identified from local operators, and data mined on social media platforms. The satellite telemetry data showed that the whale sharks moved broadly, with one individual moving to Sabah, Malaysia, before returning to the site <1 year later. Similarly, another tagged whale shark returned to the site at a similar periodicity after reaching the Malay-Filipino border. One individual whale shark first identified in East Kalimantan, Indonesia by a citizen scientist was resighted in Honda Bay ~3.5 years later. Honda Bay is a globally important site for the endangered whale shark with connectivity to two neighbouring countries, highlighting the need for international cooperation to manage the species.
Highlights
The whale shark Rhincodon typus Smith 1828 is the world’s largest extant fish, capable of reaching a maximum size of 19.6 m in length[1]
Using dedicated effort and data mined from different sources, we identified a total of 183 individual whale sharks, of which 109 were male following clasper inspection and 4 were female, and 70 whose sex could not be determined
We had a total of 507 whale shark encounters leading to 419 photo identifications with 117 individual whale sharks, with a mean of 2.6 successful encounters per survey
Summary
The whale shark Rhincodon typus Smith 1828 is the world’s largest extant fish, capable of reaching a maximum size of 19.6 m in length[1]. Though the species is protected nationally in countries that used to operate targeted fisheries (e.g. Taiwan, India, Philippines), concerns remain from ongoing fisheries in the south of China where over 1,000 animals are reportedly landed yearly in the Hainan province alone[13], and a Wild Life Risk report where a single shark processing factory in the Zhejiang province processed up to 600 whale sharks per year[14] These numbers are substantial considering, for example, that in 22 years (1992–2014) of photographic identification at Ningaloo Reef, Western Australia, a total of 1,082 individuals were identified[15]. Modified maximum likelihood methods can be employed to elucidate their lagged identification rate (LIR), defined as the probability of recapturing an animal after a certain time lag[26], to understand their local ecology This approach uses the identification data itself, including from several sources[27], to estimate various population parameters such as population size, residency, mortality, etc. Telemetry can be employed to help our understanding of an endangered species, their habitat preference and use, local and afar movements, and any connectivity to other countries— essential data for their effective management
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