Humpback whales are facing new dangers in Hawaiian waters, where more than 10,000 of the cetaceans congregate from December to April to calve and breed. That’s the conclusion of an analysis of historical records of ship strikes on humpback whales (Megaptera novaeangliae) in the seas around the Hawaiian Islands between 1975 and 2011. In that 36-year period, 68 such strikes were reported, including the one that injured the humpback calf in the photo above. The scientists have not yet been able to quantify the number of whales lethally wounded or killed outright by such hits. Because more than 63% of the collisions involved calves and subadults, the scientists conclude that these younger animals are particularly susceptible to being struck, most likely because they spend more time at the surface to breathe than do adults. Worryingly, the number of strikes has steadily increased over the years , the team reports in the Journal of Cetacean Research and Management—and not because there are more whales. Instead, the increase is apparently due to tourism. The majority of vessels that have collided with whales in Hawaii are small- to medium-sized boats, less than 21.2 meters in length, the scientists say, which happens to be the size of commercial whale-watching vessels. Federal regulations require these boats to remain at least 100 yards distance from the humpbacks. They may be keeping their distance while observing the whales, but not when under way: The majority of collisions occurred when the vessels were travelling at 10 to 19 knots, the team reports—apparently, too fast to avoid colliding with the very animals the skippers and tourists have come out to watch.