The major known contemporary threats to Whale Sharks, on a global scale, are mortality from accidental catch in fisheries as well as suspected mortality from vessel strikes (Pierce et al. 2021a, Rowat et al. 2021b, Womersley et al. 2022, 2024a). Other threats affect Whale Sharks at local or regional scales, including unmanaged wildlife tourism and pollution (Rowat et al. 2021b, Womersley et al. 2024a). Climate change is already thought to be affecting the seasonal extent of Whale Shark distribution, and some areas within their contemporary range may become less suitable habitat for the species and their prey in the future (Reynolds et al. 2024, Womersley et al. 2024b).
Fisheries
Commercial fisheries for Whale Sharks are presumed to be the primary source of anthropogenic mortality that has caused global population decline. While targeted fisheries, such as those previously present in India, Pakistan, the Maldives, the Philippines, and Taiwan, have largely closed as a result of conservation and management efforts, present-day catches in China remain unclear. Even though the species is protected, small quantities of Whale Shark products have been reported from Chinese trade surveys between 2009–2016 (O'Malley et al. 2017, Steinke et al. 2017) following large catches being documented through interview-based surveys at fishing harbours and processing centres from 2008–2010 (Li et al. 2012).
Whale Sharks are commonly incidentally captured in tuna purse-seine fisheries (Clarke 2015, Escalle et al. 2016a, Román et al. 2018). Whale Sharks, which are often associated with tuna in oceanic waters, are encircled in large nets along with the tuna species that are the intended catch. While Whale Sharks are usually released, a few are accidentally killed (Clarke 2015, Román et al. 2018). For example, data from observers aboard purse-seine tuna vessels in the Western and Central Pacific Ocean have documented a high density of Whale Shark sightings north of Papua New Guinea, with 1,809 interactions with the fleet (i.e., Whale Sharks encircled in nets) noted between 2006–2016 (Neubauer et al. 2018). However, more recent applications of safe release practices appear to minimize at least short-term mortality (Capietto et al. 2014; Escalle et al. 2016a, 2018). An expert survey estimated a 10% post-release mortality rate in the Western Central Pacific Ocean, although uncertainty was large (Neubauer et al. 2018). Where poor release practices are used, though, such as lifting the sharks from the water by their tails or leaving ropes attached to the sharks following release, longer-term mortality is still likely to be an issue.
Whale Sharks are also caught in pelagic gillnet (driftnet) fisheries. Limited information is available on Whale Shark catches in tuna gillnet fisheries, which are primarily located in the northern Indian and Pacific oceans. This is a major international fishery, accounting for approximately 34% of Indian Ocean tuna catches (Anderson et al. 2020), and the Indonesian fleet (which operates mostly in the western Pacific) was estimated to exceed 280,000 vessels in 2011 (Anderson et al. 2020). The gillnets, which are designed for entangling tuna and other pelagic fish, can be over 30 km in length (Anderson et al. 2020). Observers have been placed on a few Pakistan-based vessels or recruited from within working crews to monitor incidental catch (Razzaque et al. 2020). Whale Sharks are certainly caught in this fishery, and although live release is possible (Razzaque et al. 2020), few other data are available. A concerning incidental catch of cetaceans (whales and dolphins) from the Indian Ocean tuna gillnet fishery, estimated at 4.1 million individuals from 1950–2018 (Anderson et al. 2020), indicates that this fishery should also be treated as a major threat to Whale Sharks. Large pelagic and coastal gillnet fisheries off Peru (Rojas-Perea et al. 2024) are also known to entangle Whale Sharks (Pajuelo et al. 2018, Guidino et al. 2024).
Whale Sharks are often caught accidentally in large nets set for other species across much of their distribution, with frequent reports coming from coastal gillnet fisheries (i.e., Akhilesh et al. 2013, Barbosa-Filho et al. 2016, Rohner et al. 2018, 2020). While some are released alive, with survival confirmed through post-release monitoring (R. Matsumoto pers. comm. 2025), others are dead when found or killed for their meat or fins (Akhilesh et al. 2013, Pajuelo et al. 2018, Rohner et al. 2018, Wyatt et al. 2019, Sánchez et al. 2020). Most catches are likely to go unreported unless specific surveys are conducted (e.g., Temple et al. 2019; Haque et al. 2021). In Taiwan and elsewhere, concerns remain on current release practices from net fisheries; a rope on the caudal fin is usually used to drag or lift the Whale Sharks out of the set nets, if the rope is cut to release the shark, it may still be attached to the peduncle, causing likely injury or mortality (H. Hsu pers. comm. 2025), and lifting the sharks fully out of the water by the peduncle may cause internal injuries and separation of the caudal fin from the body of the animal reducing likelihood of survival (R. Graham unpubl. data 2025). Furthermore, reports of Whale Shark strandings from Indonesia (Fahmi pers. comm. 06/06/2025) and across the northwestern Indian Ocean (D. Robinson et al. unpubl. data 2025) suggest that mortality from incidental catches can be high and remains unquantified.
Whale Sharks are incidentally caught and their fins opportunistically harvested, for example, in Pakistan (Moazzam Khan pers. comm. 03/06/2025), and the Myeik Archipelago, southern Myanmar, where 3–5 individual Whale Sharks are caught annually (T. Gyi pers. comm. 2025). In southern Java, Indonesia, 10–30 Whale Sharks were landed annually as of 2022 – most caught incidentally and landed locally, with meat, liver and fins entering the local trade (Nijman 2023). In northern Mindanao and Southern Leyte, Philippines, Whale Sharks are occasionally caught in small-scale fisheries (multi-small vessel operated nets) but are released (not always alive; G. Araujo unpubl. data. 2025). One reported Whale Shark from Sarawak, Malaysia, caught and locally consumed in 2018 further highlights that in densely-populated regions, small-scale fisheries might pose a higher threat to whale sharks than is currently understood (Araujo et al. 2022b, Reynolds et al. 2022).
Vessel strike
Vessel strikes have been a documented source of Whale Shark mortality for decades (i.e., Gudger 1941). Rapid increases in both the speed and quantity of marine traffic mean that mortality from ship strikes is suspected to have supplanted fisheries as the main contemporary threat to Whale Sharks in parts of their distribution (Rowat et al. 2021b). Global shipping maps show that vessel traffic is extensive across both coastal and oceanic waters, with Whale Sharks at risk of collision across the majority of their global range. Overall, 92% of mean monthly (satellite-tracked) Whale Shark activity overlapped with large >300 gross ton vessels in 2011–2014, and tracked sharks spent almost half of their time in surface waters <20 m deep, where they can be susceptible to collisions (Womersley et al. 2022). Whale Sharks in areas where there are large aggregations adjacent to heavy vessel traffic, such as the Gulf of Mexico and northern Caribbean Sea (de la Parra et al. 2011, Womersley et al. 2024a) and the Arabian/Persian Gulf (Robinson et al. 2013, Reynolds et al. 2022, Womersley et al. 2024a), are at particularly high risk, with the type of large vessels most likely to impact the species varying across aggregation sites (Womersley et al. 2024a). Direct records of mortality are rare, as the sharks typically sink if killed (Speed et al. 2008, Womersley et al. 2022), but probable deaths have been recorded from satellite-tagged sharks (Womersley et al. 2022, R. Graham unpubl. data 2025), and major vessel related injuries are frequently observed in live Whale Sharks (Womersley et al. 2024a). Documented injuries may only constitute a small fraction of the real collision mortality risk, as Whale Sharks are unlikely to survive propeller or impact wounds from large vessels.
Unregulated tourism
Poor Whale Shark tourism practices, particularly those resulting in small vessel strikes, have been reported as a threat to the species at many aggregation sites (Womersley et al. 2024a). Though generally non-lethal, increasing Whale Shark tourism with a lack of effective risk management has been associated with declining abundance (Harvey-Carroll et al. 2021), increased injury rates (Harvey-Carroll et al. 2021, Penketh et al. 2021), and behavioural changes (Quiros 2007, Haskell et al. 2015, Thomson et al. 2017). Increases in the activity levels of Whale Sharks in association with tourism indicate an increase in their energetic costs (Barry et al. 2023, Reynolds et al. 2025). Careful regulation of tourism activities can reduce the real and potential threats associated with this sector (Rowat et al. 2021b, Ziegler and Dearden 2021). However, even “gold standard” (Ziegler and Dearden 2021) Whale Shark tourism at Ningaloo Reef has some impacts on Whale Shark activity levels and behaviour (Reynolds et al. 2025), and there is the potential for tourism to induce as-yet unknown physiological effects on the species. As tourism activities tend to occur in specific aggregation areas, usually dominated by juvenile male sharks, and close to the necessary infrastructure, tourism likely affects a minority of the global Whale Shark population and results in minimal mortality.
Pollution
The Deepwater Horizon oil spill in 2010 in the northern Gulf of Mexico affected a known Whale Shark habitat (Campagna et al. 2011, Frias-Torres and Bostater 2011), potentially causing mortalities or changes in movement behaviour (Hueter et al. 2013). Although there is extensive oil and gas production close to significant Whale Shark aggregation areas, such as the Gulf of Mexico (Hoffmayer et al. 2005, Hueter et al. 2013, McKinney et al. 2017, Hoffmayer et al. 2021), the Arabian/Persian Gulf (Robinson et al. 2013, 2016, 2017), and Ningaloo Reef in Australia (B. Norman pers. obs.), the regionally restricted nature of the industry means that localised spills are likely to affect a minority of the global Whale Shark population.
'Red tides,' caused by toxic blooms of Karenia spp. dinoflagellates, are associated with nutrient run-off and are increasing in frequency along the southern US coast (Brand and Compton 2007). These often result in shark mortality (Flewelling et al. 2010), among many other marine species, and the first probable Whale Shark mortality from this cause was reported in Florida in 2018 (Furby 2018).
Plastic pollution can affect filter-feeding sharks and rays (Germanov et al. 2018). Whale Sharks can accidentally ingest large quantities of microplastics while feeding in some areas, with up to about 137 pieces per hour reported from Java in Indonesia (Germanov et al. 2019). Whale Shark mortalities from plastic ingestion have been reported from Japan (Matsumoto et al. 2017, Rowat et al. 2021a), Malaysia (Lee 2019, Rowat et al. 2021b), the Philippines (Abreo et al. 2019), and Thailand (Haetrakul et al. 2009). A variety of other sublethal effects are also possible, such as endocrine disruption or toxicosis (Germanov et al. 2018). Investigation of anthropogenic pollutants, such as heavy metals, PCBs and DDT, in Whale Sharks is a recent area of study (Boldrocchi et al. 2020), with PCBs and DDT in shark skin tissue present in the Gulf of California (Fossi et al. 2017) and Djibouti (Boldrocchi et al. 2020). Entanglement, particularly in discarded or lost fishing gear, is also a likely source of mortality (Wilcox et al. 2016, Parton et al. 2019).
Climate change
Cyclical or longer-term climate shifts affect Whale Shark occurrence and local abundance (Sleeman et al. 2010, Sequeira et al. 2012), which needs to be considered when discussing local population trends. Further, a minor expansion of Whale Sharks' seasonal penetration into higher latitudes appears to be underway, in conjunction with increasing ocean temperatures (see Distribution section), and this poleward movement is projected to increase under current climate change scenarios (Sequeira et al. 2014, Reynolds et al. 2024, Womersley et al. 2024b). However, model predictions suggest that the overall range of the Whale Shark may slightly decrease over time, due to a decrease in habitat suitability in some areas of their existing distribution (Sequeira et al. 2014, Reynolds et al. 2024, Womersley et al. 2024b). Oceanographic factors other than temperature will also likely impact Whale Sharks in future climate scenarios. In particular, decreasing dissolved oxygen availability is increasingly raised as a key concern for pelagic sharks, given its potential to reduce overall habitat volume (Laffoley and Baxter 2019, Lawson et al. 2019, Waller et al. 2024). At this stage, while climate change may affect a majority of Whale Sharks, it appears that their broad thermal tolerance and wide distribution may buffer them from direct mortality. However, the potential for ecosystem-level effects on prey species, notably impacts to fish spawning aggregations that provide concentrated food sources (Graham and Roberts 2005), and cumulative exposure to other threats means that climate change remains a significant concern.
