Introduction
Whale shark conservation has entered a more perilous phase. The world’s largest fish, Rhincodon typus, is listed as Endangered on the IUCN Red List, with long-term declines documented across much of its range. New multi-institution studies show extensive overlap between whale shark habitats and major shipping lanes, elevating the risk of lethal ship strikes a threat that has been underestimated because carcasses typically sink and go unrecorded. Evidence from global tagging, AIS data and site-level analyses now points to targeted, low-cost operational measures speed management and fine routing capable of reducing risk while preserving the efficiency of seaborne trade.
Context – Background
Whale sharks inhabit tropical and warm-temperate seas worldwide, with the Indo-Pacific holding the majority of the population. In 2016 the IUCN reclassified the species as Endangered, citing declines (notably ~63% inferred for Indo-Pacific subpopulations over three generations) linked to historic targeted fisheries, bycatch, and emerging hazards such as vessel collisions. International protections include CITES Appendix II (in force since 2003), which curtailed legal trade, and a suite of regional fishery rules intended to minimize interactions.
Aggregation sites sometimes called “constellations” occur seasonally where plankton or fish spawn concentrate, from the Yucatán (Mexico) to Ningaloo (Australia), Djibouti, Seychelles, Philippines, and Oman. Some of the world’s largest gatherings occur in Qatar’s Al Shaheen oil field during summer spawning events, highlighting the juxtaposition of megafauna hotspots and industrial marine activity.
Ecotourism tied to these predictable aggregations generates significant local revenue but is sensitive to management quality. Peer-reviewed estimates place direct spending on whale-shark tourism at US$7.6–9.4m annually in the Maldives’ South Ari MPA; in Western Australia, whale-shark diving contributes ~US$12.5m within a broader coastal economy exceeding US$100m annually. These figures underscore the socio-economic stakes of effective conservation.
Key developments or current situation
Global research led by >70 scientists has mapped 26 whale-shark aggregation countries and overlaid these with AIS shipping data. The analysis highlights high-risk co-occurrence near Ecuador, Mexico, Malaysia, the Philippines, Oman, the Seychelles, and Taiwan, where cargo and passenger traffic intersect predictable surface-feeding behaviour (whale sharks can spend ~half their time in the upper water column). Parallel work using satellite tags from ~350 individuals shows >90% of tracked horizontal space under persistent large-vessel footprints, with depth-tag evidence consistent with “cryptic” mortalities after collisions. National Geographic+1
At global scale, a 2019 Nature Sustainability study projects maritime traffic growth of +240% to +1,209% by 2050, depending on socio-economic scenarios implying greater encounter potential unless risk is actively managed. Subsequent whale-shark collision-risk modelling and hotspot mapping (PNAS 2022) strengthened the case that undetected ship strikes likely contribute to continued declines despite fishery restrictions.
Crucially, site-level simulations show that modest operational adjustments can carry small schedule penalties. A 2024 global prioritization study tested mitigation in the Ewing Bank core habitat (northern Gulf of Mexico): imposing a 75% speed reduction within the small core area added ~5% to total transit time; rerouting around the core added just ~0.5% time and ~1.1% distance on average. These are proofs-of-concept rather than universal prescriptions, but they demonstrate that targeted, localized measures can be efficient.
Policy responses are beginning to align. The Convention on Migratory Species (CMS) COP14 adopted Resolution 14.5 (2024) urging Parties to reduce vessel-strike risk to marine megafauna and specifically referencing whale sharks encouraging speed management, routing and collaboration with the IMO. Regionally, the Maldives introduced enforceable speed limits and “contact-zone” rules in South Ari MPA (10 kn within the MPA; 5 kn within 250 m of megafauna; 2 kn within 50 m), combining conservation with tourism safety. IISD Earth Negotiations Bulletin+1
Bycatch controls are also tightening. Tuna RFMOs now prohibit purse-seine sets on tuna schools associated with whale sharks and require safe release/reporting: IOTC Res. 13/05 (Indian Ocean), WCPFC CMM 2022-04 (Western & Central Pacific), IATTC C-19-06 (Eastern Pacific), and ICCAT Rec. 23-12 (Atlantic) reinforce these rules across basins.
Analysis: Strategic implications
A collision risk shaped by trade routes
Risk concentrates where major shipping corridors intersect seasonal feeding grounds—e.g., the Mozambique Channel and western Indian Ocean routes linking Asia, the Middle East and southern Africa; the Straits of Malacca/Singapore for Southeast Asian sites; and Caribbean traffic near the Yucatán. At Al Shaheen, whale sharks aggregate amid oil and gas platforms and nearby tanker/cargo movements, illustrating how industrial footprints and megafauna distributions can coincide in relatively shallow seas. The overlap is structural: the same frontal systems and productivity pulses attractive to plankton feeders also lie along efficient maritime tracks.
From whales to whale sharks: porting proven tools
For large whales, the IMO now uses PSSAs and routing/speed measures; the North-Western Mediterranean PSSA (in force 1 January 2024) was approved specifically to cut cetacean ship-strike risk. Early analyses, however, suggest voluntary slowing has not yet produced widespread speed changes, hinting that mandatory, time-bound measures may be needed to ensure compliance in high-risk seasons. Whale-shark management can draw from these mammal precedents designating seasonal, fine-scale management boxes where slow-down and micro-routing apply when sharks are present.
Speed really matters
Collision lethality scales with speed; for right whales, risk reductions of up to 90% occur when ships travel ≤10 kn. While the exact lethality curve for whale sharks is not yet defined, the Ewing Bank simulations demonstrate that restricting speed inside small cores imposes limited aggregate delays, particularly when paired with smart rerouting. This is consistent with broader evidence that tight, place-based measures outperform sweeping, basin-wide prescriptions in both conservation impact and operational efficiency. irinsubria.uninsubria.it
Governance is catching up
The CMS resolution provides a mandate for national measures in EEZs—where most hotspots sit and for coordination with IMO on routing where international shipping lanes are involved. Meanwhile, the World Shipping Council’s Whale Chart now compiles global whale-protection measures as a voyage-planning aid; expanding such tools to encompass whale-shark seasons/sites would speed uptake across fleets.
Consequences – Perspectives
For conservation: The weight of evidence suggests ship strikes are material, under-detected contributors to whale-shark mortality, alongside local pressures (small-vessel strikes, unregulated tourism). Priorities include (1) seasonal risk calendars for key sites; (2) mandatory slow-downs within small core polygons when sharks are present; (3) micro-routing of lanes a few nautical miles around cores; and (4) standardized incident reporting and carcass detection protocols. plymsea.ac.uk
For shipping: The operational burden of targeted measures appears modest. Where studies tested them, micro-deviations (≈12 nm) or in-box slow-downs imposed ≤~5% average time increases for transits intersecting a small core, with ~0.5% average time and ~1.1% distance added for full bypass. Aggregation cores are typically small and seasonal, enabling predictable planning with limited cost and co-benefits for safety, noise and fuel.
For coastal economies: Whale-shark tourism revenues—from South Ari to Ningaloo—depend on predictable, well-managed encounters. Embedding speed/spacing rules for all craft (commercial and recreational) near shark sightings protects both animals and visitor experiences; the Maldives’ SAMPA rules provide a practical template (10 kn in MPA; 5 kn within 250 m; 2 kn within 50 m; limited vessel numbers).
For fisheries: RFMO bans on setting purse seines on whale-shark-associated tuna schools and mandatory safe-release protocols are now near-universal across the Atlantic, Indian and Pacific basins. Consistent observer coverage and reporting remain essential to verify compliance and refine bycatch risk estimates.
Conclusion
The conservation case is clear and pragmatic: focused, seasonal slow-downs and micro-routing at a handful of well-mapped aggregation cores would meaningfully reduce whale-shark collision risk while barely perturbing schedules. As maritime traffic expands through mid-century, coupling CMS-backed national measures with IMO-level routing where appropriate and mirroring best practice from cetacean management offers a disciplined, low-cost path to keep these “constellations” alive in the Indo-Pacific and beyond. Nature
Geographic tags: Indo-Pacific, Indian Ocean, Gulf of Mexico, Arabian Gulf, Mexico, Philippines.
