Vessel Noise

Orcas find salmon by echolocation, listening for the returning click off a fish's swim bladder. It is a faint signal, and it is easily buried. Shipping traffic, ferries, whale-watching boats and recreational vessels all put energy into exactly the frequency bands the whales depend on.

Measured effects are direct: in the presence of vessels, foraging time drops. The whales spend more energy travelling and less time eating, which compounds the prey problem. Females appear to be affected more than males.

This is the most tractable threat on the list. Slowing ships reduces noise immediately and measurably. Voluntary slowdown programmes in the Salish Sea have already produced quantified reductions, without waiting for a salmon run to recover.