Sand eels are the default. When nothing else is obvious, you tie on something thin and silver and fish it with confidence, day or night, because sand eels are always around.
They are always around. They are not always available, and the difference is larger than most of us fish like it is.
What happens to a sand lance when the light goes
In 1974 P. Winslade published three papers in the Journal of Fish Biology on the behavior of the lesser sandeel. They are old, they are unglamorous, and they are the closest thing this fishery has to a controlled answer.
He sorted the animal into three activity states:
- Swimming
- Partially emerged
- Fully buried
Then he varied light. Feeding was maximal between 100 and 1,000 lux, much reduced at 10 lux, and very low at 1 lux. With food present, the animals kept a plain diurnal rhythm: buried in the dark, emerged and feeding in the light.
Put those numbers on a night you have actually fished:
| Condition | Roughly |
|---|---|
| Where Winslade's sand eels fed hardest | 100–1,000 lux |
| Where their feeding nearly stopped | 1 lux |
| Clear full moon | 0.05–0.3 lux |
| Low cloud over a city, lit by sky glow | about 0.14 lux |
The moonlight and sky-glow values are from Kyba and colleagues (2017). Even the brightest full moon is a small fraction of the light Winslade's animals stopped feeding in.
Sand lance feed in daylight. By late twilight they are mostly done. On a dark night they are not feeding poorly — they are in the sand.
Why that matters more than it sounds
Fishing a sand-eel profile at two in the morning asks a bass to eat a representation of an animal that, at that hour and in that place, is buried under the bottom. Some nights you catch anyway — bass eat plenty of things that look roughly like a small slim fish, and a sand eel silhouette is a passable silverside, a passable juvenile herring, a passable nothing-in-particular.
But you are no longer matching a hatch. You are fishing a generic small-baitfish shape and hoping. Worth knowing which of those you are doing.
The temperature half, which is less useful but real
The third paper found daytime activity high at 10 and 15 °C and lower at 5 °C. That is a cold-water finding and it matters more for a spring or late autumn read than an August one. It also points the same direction as the light work: this animal's default is to be in the substrate, and it comes out under specific conditions rather than the other way round.
Our sand lance
Winslade worked on Ammodytes marinus, the lesser sandeel of the eastern Atlantic. Ours is the American sand lance, and the Northwest Atlantic synthesis describes the same burrowing and the same daily cycle of emerging from the sand across the genus (Staudinger et al. 2020). The direction carries over; the exact lux numbers belong to the European fish.
What to do with it
In daylight, a sand eel imitation is a sand eel imitation. The animal is out and feeding, and matching it is matching something real.
In the dark, ask what is actually available. Squid, worms, herring and eels do not bury themselves at sunset. A dark night is the wrong time to insist on the thinnest fly in the box on the grounds that the beach was full of sand eels at noon.
And treat dawn and dusk, with the water moving, as the interesting edge. The animals are moving between buried and emerged around the light levels where Winslade measured the steepest change. That is a transition, not a steady state, and changing light over moving water is where the striper books put the fish (Tabory, Inshore Fly Fishing).
How StripedLines uses this
StripedLines is built for striped bass. When the app suggests which bait to match, it follows this: sand eels out over the sand by day, buried by night.