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Climate change could make whale sharks more vulnerable to shipping threats

Whale sharks are among the world’s most emblematic and vulnerable species, living in the warm oceans of the tropics. In future, climate change could reshuffle their habitats, potentially also leading them away from key sites they currently use, and, as new research suggests, into more dangerous waters, heavily used by ships. Integral to this global study was a large database of Argos whale sharks movement tracks which enabled a detailed threat assessment
Whale sharks (Rhincodon typus) are the world’s largest fish and found in all tropical oceans (see e.g. https://www.argos-system.org/whale-sharks-near-saint-helena-island/, https://www.argos-system.org/whale-sharks-in-madagascar/ and https://www.argos-system.org/whale-sharks-giants/ ), often spending time in shallow, warm waters (between 18 and 34 °C). Since whale sharks are relatively slow moving and often spend time in surface waters, they are especially vulnerable to ship collisions. They are already listed as ‘Endangered’ with a declining population. This is concerning since the species’ overlap with threats could increase in future due to redistributing habitats with climate change.
Satellite-tracking of whale shark movements and habitats
A new study used a whale shark satellite-tracking dataset of 348 individuals, comprising the largest compiled set to date for the species and including Argos tracking over 15 years in all major oceans.
Distribution models based on these tracking data and a range of oceanographic variables were used to generate global habitat suitability maps (i.e. areas with the capacity to support whale sharks), which determine the likelihood of their presence. The model was first run on current oceans (2005–2019) to reveal where suitable whale shark habitats are most likely to be found, and then fed with projected values of future oceanographic conditions to predict future habitat locations in 2050 and 2100 (depending on different emission scenarios).

The model predictions showed that habitats located at the edges of areas currently occupied by whale sharks could become increasingly suitable in all future scenarios. Depending on the scenario and the region, some currently occupied habitats may see a reduction, and some an increase in future suitability. However, the forecasted shifts are expected to be less pronounced under the most sustainable development scenario (where we implement strategies to mitigate climate change).
A previously validated whale shark–ship collision risk index was applied to the predicted whale shark habitat suitability maps to find increases in whale shark–ship co-occurrence in all future decades following any of the scenarios. This increase in co-occurrence was driven by completely new habitats projected into areas of busy shipping. For example, the model projects newly suitable waters for whale sharks on the west coast of North American and mainland Africa, close to busy ports and shipping highways. A few areas showed a decrease in co-occurrence, because of habitats moving away from the busiest shipping areas, or overall habitat losses.
![a, EEZ marine regions coloured by degree of change in ship co-occurrence index (SCI) from the 2005–2019 baseline years. Red represents an increase in collision risks for whale sharks and blue a decrease for 2100 ssp585. b, Percentage change in ship co-occurrence index from the 2005–2019 baseline years within each EEZ marine region, sorted and coloured by decade and scenario combination. c, Mean ship co-occurrence index calculated across EEZ marine regions, coloured by decade and scenario combination where the black dotted line represents present-day baseline ship co-occurrence index (2005–2019) and the percentage change from baseline is shown above each bar (from [Womersley et al., 2024]).](https://www.argos-system.org/wp-content/uploads/2024/10/EEZ-marine-regions.jpg)
Along with the potential dangers posed by ship collisions, the fact that whale shark habitats could reshuffle globally in future, poses a number of other intrinsic risks to the species – for example, key sites for whale sharks may become less accessible, and unfamiliar environments of the new habitats may lead to increased mortality if the animals get caught out by unfavorable conditions. To minimize these impacts and prevent further population declines for whale sharks, biodiversity conservation measures will have to be developed soon. The methods explained in this new study could be applied to other species, and potentially used to help in assessing resilience of current Marine Protected Areas to climate change or designing new protection measures for Endangered marine megafauna.
Reference & links
Womersley, F.C., Sousa, L.L., Humphries, N.E. et al. Climate-driven global redistribution of an ocean giant predicts increased threat from shipping. Nat. Clim. Chang. (2024). https://doi.org/10.1038/s41558-024-02129-5