Bonefish are well known for their ability to feed on bottom dwelling creatures. Having their mouth structured underneath their head helps them to dig out little crabby and shrimpy candies with ease.
The bottom of a bonefish flat has layers, just like regular land. If you break the surface you might find some slightly different colored sand or coral.
When bonefish feed they will forage and actually dig into the bottom to wrestle out food. When they do this the surface on the bottom gets disturbed and reveals a different colored under-bottom. The marks that are left behind a feeding bonefish are called feed marks.
The strength of the contrast between the surface color and the under bottom color can help an angler tell how recent the feed marks were made.
If there’s lots of contrast between the layers, that means they’re really looking fresh, and that’s a good sign that bones have been on that flat recently. Your odds of seeing fish are high in situations like this – assume the ready position!