The growth of the global commerce fleet is seriously threatening ocean biodiversity. For susceptible species, collisions between ships and marine megafauna may impact the population. This growing fleet is part of the global distribution of the Endangered whale shark (Rhincodon typus), and studies of movement patterns have indicated that significant vessel collisions represent a substantial threat to the species.
At aggregation locations, where up to 400 individuals can congregate to feed on seasonal spikes of planktonic productivity, it is unknown if they are also at risk. There is substantial ecological, socioeconomic, and cultural importance to these “constellation” places.
Researchers have discovered that heavily trafficked shipping channels cross vital feeding sites for whale sharks, endangering this threatened species.
A recent study has identified places where whale shark aggregations are most likely to collide with large shipping vessels by mapping their locations and superimposing information on shipping traffic.
Lead author Dr. Freya Womersley, a researcher at the Marine Research and Conservation Foundation (MARECO), the University of Southampton, and the Marine Biological Association (MBA), said, “The almost ubiquitous overlap of at least some large shipping vessel traffic with whale shark aggregations underlines the magnitude of the threat the shipping industry poses,” says lead author Dr Freya Womersley.”
“Our findings highlight the need for targeted measures within these areas to reduce the risk of collision and improve the conservation status of endangered whale sharks.”
Dr Gonzalo Araujo, Director at MARECO, said: “Collisions with large ships are likely to be fatal for whale sharks, but evidence is scarce. Whale sharks are slightly negatively buoyant, so their bodies sink. To inform conservation efforts, it’s important to quantify collision-related threats even when direct evidence is lacking.”
In response to a series of survey questions, over 75 experts identified buffer zones—other locations where whale sharks have been spotted—and core habitats—areas where they have experienced the greatest number of whale sharks. 26 countries and 107 regions were identified. More than 13,000 people, or more than half of all whale sharks known to science, contributed observations to the report that the experts shared.
The scientists then used Global Fishing Watch’s (www.globalfishingwatch.org) data on significant ship positions to determine the shipping density in each constellation.
The areas off the coasts of mainland Ecuador, Isla Mujeres and La Paz in Mexico, Ewing Bank in the northern Gulf of Mexico, Kota Kinabalu and Redang Island in Malaysia, Pintuyan in the Philippines, Musandam in Oman, Seychelles and Taiwan were the most dangerous places for whale sharks to come into contact with large vessels.
Researchers found 39 locations where seasonal whale shark occurrence maxima, often spanning multiple months, aligned with shipping traffic peaks.
Dr. Chris Rohner, Principal Scientist at MMF, said: “Many of these sites had more than one vessel per square kilometer in core habitats. For example, the constellation Isla Mujeres in Mexico has an average of 56 ships passing through the core habitat monthly. These sites require urgent action to reduce the threats posed by shipping.”
The study’s findings demonstrated that specific experts understated the threat posed by large ship collisions within constellation sites because there was insufficient direct evidence—such as witness accounts or injuries—available for other, less severe threat categories, such as interactions between tourists and small vessel collisions.
The study group also considered countermeasures for this threat. They imitated ship movements in the northern Gulf of Mexico’s Ewing Bank whale shark constellation.
Dr Womersley said: “One of the benefits of speed reductions is that they can be temporarily introduced during whale shark peak seasons. These speed limits can also be applied to smaller vessels, which are less deadly but can still damage the sharks.”
Amy Fraenkel, Executive Secretary of the Convention on the Conservation of Migratory Species of Wild Animals (CMS), noted: “CMS plays a pivotal role in securing the long-term survival of the whale shark – a globally endangered species. Ensuring the safety of this highly migratory species from vessel collisions within its migratory range, particularly at aggregation sites, is a key goal under CMS.”
Scientists noted, “Support for these measures requires increased awareness and education of the issue as well as improved data but suggest effective management strategies could pave the way for coexistence between this important species and the shipping industry.”
Journal Reference:
- Freya C. Womersley, Christoph A. Rohner, Kátya Abrantes et al. Identifying priority sites for whale shark ship collision management globally. Science of The Total Environment. DOI: 10.1016/j.scitotenv.2024.172776