The whale shark, Rhincodon typus, is the largest known fish species in the world, reaching over 12 meters. These gentle giants are filter-feeders, consuming plankton and small fish by straining vast quantities of seawater through their mouths. Despite their size and docile nature, whale sharks face significant threats, leading to their classification as endangered on the IUCN Red List. Their global population has declined by more than 50% over the last 75 years, with the Indo-Pacific subpopulation experiencing an even more dramatic decrease of 63%.
Direct Human Activities
Direct human activities contribute to the decline of whale shark populations. Although protected in many countries and by international treaties, illegal or unregulated fisheries continue to target them. They are sought for their meat, fins, and oil, which have economic value in certain markets; for instance, whale shark meat was in high demand in countries like India and the Philippines prior to increased protections.
Whale sharks also become accidental victims in fishing operations, known as bycatch. They are often entangled in fishing gear like gillnets, longlines, and purse-seine nets, typically set for other species. Their large size makes escape difficult, often leading to injury or death, even with release efforts. A persistent black market for whale shark products fuels ongoing poaching, despite international regulations like CITES.
Environmental Degradation
Human impacts that degrade their environment also pose threats. Marine pollution, including plastic waste, poses a danger. As filter-feeders, whale sharks are susceptible to ingesting microplastics, which can contaminate food sources or directly harm them; studies estimate whale sharks can ingest up to 137 pieces of plastic per hour while feeding. Chemical pollutants from oil spills, agricultural runoff, and industrial discharge can contaminate their prey and affect their health, leading to toxic effects.
Coastal development harms whale sharks by degrading their habitats. Development, dredging, and destruction of coastal areas disrupt nursery and feeding grounds, reducing available resources and altering natural behaviors. Increased shipping traffic and recreational boats introduce a risk of vessel strikes. Whale sharks spend time feeding near the surface, making them vulnerable to collisions with vessels, which can result in severe injuries or fatalities; studies indicate their spatial use often overlaps with shipping lanes, and satellite tag transmissions frequently end in busy vessel areas, suggesting undetected or unreported deaths.
Global Climate Shifts
Global climate shifts present long-term challenges for whale sharks. Rising ocean temperatures can alter the distribution and abundance of plankton, their primary food source. This can force whale sharks to shift migration patterns in search of food or face scarcity, potentially increasing metabolic rates while food supply diminishes. Under high emission scenarios, whale sharks may be forced into cooler environments, leading to potential habitat loss in some areas.
Ocean acidification, from increased carbon dioxide absorption by oceans, impacts the marine food web. This acidification can affect calcifying organisms in their diet, potentially reducing nutritional value or availability. Climate change is associated with more frequent extreme weather events. Such events can disrupt habitats and migratory routes, adding environmental stress. These changes could increase the likelihood of whale sharks encountering other threats, such as vessel strikes, by forcing them into new areas.