Satellite tracking of juvenile whale sharks in the Sulu and Bohol Seas, Philippines

Abstract

The whale shark Rhincodon typus was uplisted to ‘Endangered’ in the 2016 IUCN Red List due to >50% population decline, largely caused by continued exploitation in the Indo-Pacific. Though the Philippines protected the whale shark in 1998, concerns remain due to continued take in regional waters. In light of this, understanding the movements of whale sharks in the Philippines, one of the most important hotspots for the species, is vital. We tagged 17 juvenile whale sharks with towed SPOT5 tags from three general areas in the Sulu and Bohol Seas: Panaon Island in Southern Leyte, northern Mindanao, and Tubbataha Reefs Natural Park (TRNP). The sharks all remained in Philippine waters for the duration of tracking (6–126 days, mean 64). Individuals travelled 86–2,580 km (mean 887 km) at a mean horizontal speed of 15.5 ± 13.0 SD km day−1. Whale sharks tagged in Panaon Island and Mindanao remained close to shore but still spent significant time off the shelf (>200 m). Sharks tagged at TRNP spent most of their time offshore in the Sulu Sea. Three of twelve whale sharks tagged in the Bohol Sea moved through to the Sulu Sea, whilst two others moved east through the Surigao Strait to the eastern coast of Leyte. One individual tagged at TRNP moved to northern Palawan, and subsequently to the eastern coast of Mindanao in the Pacific Ocean. Based on inferred relationships with temperature histograms, whale sharks performed most deep dives (>200 m) during the night, in contrast to results from whale sharks elsewhere. While all sharks stayed in national waters, our results highlight the high mobility of juvenile whale sharks and demonstrate their connectivity across the Sulu and Bohol Seas, highlighting the importance of the area for this endangered species.

Seasonal Occurrence, Horizontal Movements, and Habitat Use Patterns of Whale Sharks (Rhincodon typus) in the Gulf of Mexico

“…Since most whale shark aggregations occur in coastal waters (Rowat and Brooks, 2012) this use of more offshore waters by adults would explain why immature sharks dominate the aggregations. This use of shallower continental shelf habitat for juvenile whale sharks is not exclusive as several studies, including the current study, have reported juveniles to use offshore waters as well (Hsu et al, 2007;Araujo et al, 2018;Diamant et al, 2018). Additional tracking and dietary studies on juvenile and adult whale sharks will be instrumental in better describing stagespecific movement patterns.…”

“…These seasonal offshore movements away from known foraging areas is supported by the other whale shark tagging study in the region by Hueter et al (2013), who reported whale shark movements from the southern GOM, with similar timings of movements away from the summer aggregation site during fall. Further supporting this is that as prey abundance at localized seasonal aggregation sites wanes, whale sharks leave these areas to undergo broad scale movements in search of other foraging opportunities (de la Parra Venegas et al, 2011;Hueter et al, 2013;Araujo et al, 2018). The ultimate purpose of the movements away from the northern GOM during fall and winter is unknown, however, as observed in other regions these movements could represent searching for additional foraging opportunities and possibly movements to more productive overwintering grounds in the GOM.…”

“…Even though several of the tagged sharks were tracked longer than 6 months, there was no evidence of departure from the GOM; however, multiple seasonal cross-basin movements were observed. Considering the large number of tagged individuals and the fact that some whale sharks have been shown to make large-scale seasonal movements (Hueter et al, 2013;Hearn et al, 2016;Araujo et al, 2018;Diamant et al, 2018), it was surprising that no individuals made movements outside the GOM. One possible explanation for this residency to the GOM could be related to tagging location.…”

Changes in diving behaviour and habitat use of provisioned whale sharks: implications for management

“…The whale sharks at Oslob that feed at the surface for extended periods of time (often 6 am to 1 pm) are exposed to higher temperatures and more direct sun exposure than would be typical (e.g. 30,[42][43][44][45] ). The prolonged sun exposure on shallow waters with a sandy substrate reflects sunlight which might cause skin darkening on the www.nature.com/scientificreports/ ventral side of the animals (GA, pers.…”

Whale sharks Rhincodon typus get cleaned by the blue‐streak cleaner wrasse Labroides dimidiatus and the moon wrasse Thalassoma lunare in the Philippines

“…Whale sharks form predictable aggregations across the globe, normally linked to primary productivity or feeding opportunities ( e.g ., Belize, Heyman et al ., 2001; Mexico, Motta et al ., 2010; Qatar, Robinson et al ., 2013). With a few exceptions ( e.g ., the Galapagos, Hearn et al ., 2016; Tubbataha Reefs Natural Park, TRNP, Philippines, Araujo et al ., 2018), whale shark aggregations tend to be thus primarily driven by foraging opportunities.…”