As maritime vessels continue to flood the waters off San Francisco for Fleet Week, marine mammal experts caution those piloting these ships to keep a keen eye out for other ocean-going behemoths — like, for example, two recently spotted humpback whales.

Friday, researchers at The Marine Mammal Center identified two migratory humpback whales as they passed beneath the Golden Gate Bridge, which brought up concerns about cetacean safety during the military showcase. And although such whale sightings should be celebrated—cetaceans (whales, porpoise, dolphins) are akin to ecological canaries in the coal mine; their presence means the environments they occupy are healthy and stable—they're also a cause for concern.

“It says a lot about the health of the San Francisco Bay,” Dr. Tim Markowitz, a Research Associate at The Marine Mammal Center’s Cetacean Field Research Program, told Salon in regards to the early-October whale sighting. “Ecologically, we are doing well, they go where the food is, a lot of that is the good news, but the downside is they are living, feeding, foraging, they are doing a lot of diving, and they are doing this in an urban environment.”

But, to echo Markowitz’s concerns about these 60,000-plus-pound mammals moving through Bay Area waters, a number of humpback whales die each year due to collisions with marine ships. In fact, per a peer-reviewed study published in the academic journal Plos One, as many as 22 humpback whales die each year because of such incidents; both blue and fin whales are also susceptible to fatal impacts with marine vessels along the West Coast as well, according to the same study.

So, how can ship captains assure they don’t intentionally mar or (worse) kill any kind of whale? Easy: Slow down.

“There is a huge difference in mortality rates between 15 knots and 10 knots,” Markowitz adds in his conversation with Salon, nodding that those steering ships during Fleet Week should keep a close eye out for these threatened sea creatures. “There is a drop, 90 percent, in the probability of mortality.”

For more information on how you can help in safeguarding these wonderous creatures from extinction, visit Ocean Alliance for more details and educational tools.

Related: Video Shows Close Call Between Sailboat and Humpback Whale in the Bay

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