Boat Traffic Disrupts Marine Megafauna Across 40 Years of Research

Boats disturb large marine animals. That premise is not new in conservation biology. What has been missing is a synthesis of four decades of scattered evidence into a coherent global picture of how severe that disturbance is, which species are most affected, and what that means for conservation policy.

A meta-analysis published in npj Ocean Sustainability provides that synthesis. The University of Miami-led research team combined findings from more than 200 peer-reviewed studies conducted worldwide, compiling nearly 1,900 comparisons between scenarios with vessel presence and those without. The species covered span marine megafauna broadly: whales, dolphins, seals, manatees, sea turtles, sharks, and rays.

What the pattern shows

Across species, geographic regions, and types of behavioral and physiological measurement, the pattern is consistent. Vessel presence alters how large marine animals feed, move, and communicate. It raises stress hormone levels. Sustained exposure can influence population-level trends over time.

"Even when vessels do not directly strike animals, their presence alone can disrupt feeding, movement, communication, and stress levels. These small, repeated disturbances can add up over time and affect populations," said Julia Saltzman, the study's lead author and a doctoral student at the University of Miami Rosenstiel School.

Engine noise interferes with acoustic communication in cetaceans that use sound for virtually every biological function - foraging, navigation, reproduction, mother-calf contact. Visual disturbance triggers avoidance responses that interrupt feeding. The metabolic cost of sustained alertness from boat traffic adds to the energy budget of animals already facing prey depletion from warming oceans.

Threatened species show stronger responses

One finding stands out as particularly concerning from a conservation standpoint: species already listed as threatened or endangered tend to show larger or more consequential responses to vessel disturbance than non-threatened species.

This has direct management implications. The species that most need protection from vessel disturbance are the same ones that face the most severe effects from it.

Uneven research coverage

The meta-analysis also mapped where research gaps exist. Sea turtles showed strong, well-documented responses to vessel disturbance. Large fishes, sharks, and rays remain understudied relative to the frequency with which they share waters with boat traffic.

"Some groups, particularly sea turtles, show stronger responses to vessel disturbance, while others, including large fishes, sharks and rays, remain relatively understudied despite frequent spatial overlap with vessel activity," said Emily Yeager, a co-author at the Rosenstiel School.

Management implications

"Dynamic management strategies, including seasonal speed restrictions, adaptive buffer distances and targeted closures of key habitats, can provide flexible, evidence-based tools to reduce vessel impacts while allowing continued human use of the ocean," said Catherine Macdonald, associate professor at the Rosenstiel School and director of the Shark Research and Conservation Program.

Meta-analyses are constrained by the quality and coverage of their underlying literature. Studies with null results are less likely to be published, which can inflate apparent effect sizes. The authors acknowledge this possibility and address it in their statistical approach.