September 4, 2019 — After decades of whaling decimated their population, humpback whale populations off the West Coast are finally recovering. Hundreds of them now make their way up and down the coast each year, migrating from tropical breeding grounds in Mexico and Central America to feeding areas further north. For the most part, humpback whales—known for their melodic songs, athletic leaps through the air, and altruistic behavior towards other marine mammals—make this journey unhindered, as they did for centuries of their evolutionary history.
But in recent years, a new threat has emerged along the West Coast: From November through mid-July, tens of thousands of deadly ropes hang in the water column, connecting buoys at the surface with crab traps on the seafloor, designed to harvest Metacarcinus magister, aka Dungeness crab.
A curious humpback might become entangled while playing around with fishing gear or rolling around in it, as the mammals are known to do with kelp. Probably more often, they may become entangled while feeding, which they do by making underwater, open-mouthed lunges to collect krill or small fish. Fishing line can get caught up in the cetaceans’ baleen teeth and restrict their ability to feed. Ropes can gradually saw through tissue, causing lacerations and ultimately death by infection. Whales that don’t manage to break free on their own or get cut free by professional disentanglers immediately may drown or die slowly through exhaustion or starvation.