This dataset provides in-situ bubble size distributions (BSDs) measured at three distinct gas vents of the Bush Hill cold seep (lease block GC185, Gulf of Mexico; water depth ≈ 545 m), located within the gas hydrate stability zone. Data were collected during the RR2405 research cruise (2024) using a custom-developed deep-sea shadowgraph (shadow) imaging system deployed at the seafloor. Methods. Bubbles released from each vent were imaged optically against a collimated back-light source, using an underwater imaging system developed by the University of Missouri Environmental Fluid Dynamics Lab and deployed on the bracket of the ROV Jason. Individual bubbles were segmented from the image sequences (10 fps), and equivalent spherical diameters were computed from the projected bubble areas, with non-spherical bubbles handled via an equivalent-volume approach. Per-vent bubble size distributions were derived from the segmented populations. Coordinates / site: Bush Hill cold seep, GC185, Gulf of Mexico, ≈ 545 m water depth.