Biology Faculty Articles

ResearcherID

G-4080-2013

Document Type

Article

Publication Title

Proceedings of the National Academy of Sciences

ISSN

0027-8424

Publication Date

5-9-2022

Keywords

Ship Strike, Marine Megafauna, Conservation, Movement Ecology, Human Impact

Abstract

Marine traffic is increasing globally yet collisions with endangered megafauna such as whales, sea turtles, and planktivorous sharks go largely undetected or unreported. Collisions leading to mortality can have population-level consequences for endangered species. Hence, identifying simultaneous space use of megafauna and shipping throughout ranges may reveal as-yet-unknown spatial targets requiring conservation. However, global studies tracking megafauna and shipping occurrences are lacking. Here we combine satellite-tracked movements of the whale shark, Rhincodon typus, and vessel activity to show that 92% of sharks’ horizontal space use and nearly 50% of vertical space use overlap with persistent large vessel (>300 gross tons) traffic. Collision-risk estimates correlated with reported whale shark mortality from ship strikes, indicating higher mortality in areas with greatest overlap. Hotspots of potential collision risk were evident in all major oceans, predominantly from overlap with cargo and tanker vessels, and were concentrated in gulf regions, where dense traffic co-occurred with seasonal shark movements. Nearly a third of whale shark hotspots overlapped with the highest collision-risk areas, with the last known locations of tracked sharks coinciding with busier shipping routes more often than expected. Depth-recording tags provided evidence for sinking, likely dead, whale sharks, suggesting substantial “cryptic” lethal ship strikes are possible, which could explain why whale shark population declines continue despite international protection and low fishing-induced mortality. Mitigation measures to reduce ship-strike risk should be considered to conserve this species and other ocean giants that are likely experiencing similar impacts from growing global vessel traffic.

DOI

10.1073/pnas.2117440119

Volume

119

Issue

20

First Page

e2117440119

Comments

The derived mean shark relative spatial density and data underlying Fig. 4A (map of mean shark–vessel spatial overlap and CRI) and Fig. 4B (plot of spatial overlap and CRI) is freely available on GitHub (https://github.com/GlobalSharkMovement/GlobalCollisionRisk) (38).

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