Sand Lance, Ammodytes hexapterus. L = 10 cm. (Why this photo wants to be in portrait I don't know-- but it insists, even after rotation in Photoshop.)
This little fish, the Pacific Sand Lance, is found in nearshore waters from Japan to California, and throughout much of the Arctic. As the name suggests, it is associated with sandy substrates, and in late fall-early winter spawns at sandy beaches. Sand lances are food for larger fish, including juvenile salmon, and sea birds--the usual consumers of smaller fish.
We found a few dead individuals during the sand dollar search. I was surprised the gulls hadn't snapped them up. They are free-swimming during the day, and burrow into the sand at night. My guess is that the ones we found became trapped in dead-end ripple channels as the tide receded, and couldn't find their way back to the larger tide pools.
Things that live in sand. Part 1, Part 2, Part 3.