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When eight endangered North Atlantic right whales turned up dead in the ocean off Nova Scotia this past June, scientists scrambled to find out why. Early data shows several of the whales had blunt force trauma consistent with a ship strike, with data still pending on others.

Ship strikes are a major cause of injury or death for whales. But why do they happen at all? The ocean is vast, and huge ships don’t exactly travel at freeway speeds—there should be enough noise, movement, and warning for a whale to get out of the way, right? Why whales may remain in dangerous proximity to ships is tough to study, but over the years, some clues have begun to emerge.

One reason is that whales may not know ships are dangerous. After all, as the biggest animals in the ocean, whales may not understand that there are things in the ocean larger and more powerful than they are.

“It’s not something they’re evolved to deal with,” says John Calambokidis, a research biologist at Cascadia Research Collective in Washington State. “It’s also something there’s very little opportunity to learn from. It’s not like you can get struck two or three times and then you know you should avoid them.”

Calambokidis is trying to better understand why whales get hit through his ongoing acoustic-tagging study of blue whales off the coast of California, where whales coexist with the busy shipping lanes that feed the huge ports of Los Angeles and Long Beach.

In his study, Calambokidis found that when a ship approaches, the blue whales most often slowly sink, rather than dive or swim evasively. One of the tagged whales had 14 recorded near misses in just a few weeks. Calambokidis also found that the blue whales are more vulnerable to strikes at night, when they spend about 70 to 80 percent of their time resting near the surface. The risk also rises when shipping lanes cross whale feeding areas.

Another reason for ship strikes is that in busy shipping lanes, whales get used to the traffic, and may ignore an approaching ship until it’s too late. And there’s some evidence that the bows of large ships may mask the sound from the engine, making it difficult to hear them approaching (a phenomenon called the bow null effect). Calambokidis suspects that whether or not a whale is struck depends on how (and if) it detects a ship, coupled with how it reacts (or not).

Whales that rely on acoustics to feed and hunt have an added challenge in avoiding ships. Killer whales, for example, vocalize extensively when feeding, socializing, and navigating. Ships add both noise and danger to the underwater soundscape.

Lynne Barre, the recovery coordinator for southern resident killer whales with the US National Oceanic and Atmospheric Administration (NOAA), says whales may be confused by ship sounds. “They might be distracted by feeding, or other whales, but we don’t know.”

Barre says when it comes to killer whales, their relatively small size allows them greater maneuverability than their larger baleen relatives. She says large ships may be more predictable and easy to detect, while recreational boaters with smaller vessels may move more erratically, try to get close to the whales, or be unaware that they’re in killer whale habitat. Some of the worst strikes or wounds are from small recreational vessels.

Collecting data has been problematic, Barre says. A large ship’s crew may have no idea they’ve struck a whale, or they may not want to report it. So deceased whales that wash up, sad as they are, add critical information to our small but growing knowledge on what happens during a collision. Studying the location and severity of wounds also gives clues about the encounter as well as data on safe ship speeds through whale stomping grounds. Based on the accumulating data, NOAA has implemented regulations in Puget Sound prohibiting all vessels, from huge cargo ships to kayaks, from coming within 200 meters of whales. (On the Canadian side, Fisheries and Oceans Canada stipulates that vessels cannot come within 100 meters.)

It will ultimately be up to humans, not whales, to prevent strikes. “There haven’t been giant objects steaming through the ocean at 20 to 30 knots until very recent times,” says Calambokidis.

We brought ships into the whales’ world, now we need to learn how to be good neighbors.