Identifying priority sites for whale shark ship collision management globally

Area of Science:

• Marine Biology
• Conservation Science
• Oceanography

Background:

• The expansion of global shipping traffic increases the risk of collisions with marine megafauna.
• Endangered whale sharks (Rhincodon typus) face significant threats from large vessel collisions, particularly along their migratory routes.
• The risk of ship strikes within whale shark aggregation sites, known as 'constellation' sites, remains largely unquantified.

Purpose of the Study:

• To assess the collision risk posed by shipping traffic to whale sharks (Rhincodon typus) within their global aggregation sites.
• To identify and rank 'constellation' sites based on the potential danger of large vessel collisions.
• To evaluate potential mitigation strategies for reducing ship strike incidents in critical whale shark habitats.

Main Methods:

• Expert elicitation was used to gather data from over 50 whale shark aggregation sites worldwide, involving more than 13,000 individuals.
• Spatial analysis was conducted to define the boundaries of aggregation sites and their overlap with shipping lanes.
• Sites were ranked according to their relative collision threat levels, considering shipping density and whale shark presence.

Main Results:

• Whale shark aggregation sites in the Arabian Sea, Gulf of Mexico, Gulf of California, and Southeast/East Asia exhibit the highest collision threat.
• 39 high-risk sites were identified where peak whale shark seasonality coincides with peak shipping activity, sometimes for months.
• Simulations suggest that mitigation measures could have minimal industrial impact, as core whale shark habitats are often spatially limited.

Conclusions:

• The threat of large vessel collisions at whale shark aggregation sites may be underestimated due to a lack of direct evidence.
• A coordinated, multinational approach is essential for implementing effective collision mitigation measures in priority whale shark habitats.
• Protecting whale shark 'constellation' sites from vessel strikes is critical for the conservation of this endangered species.