mystery food in mackinaw's stomach

This photo was sent to me and my colleagues through my work email yesterday.  A mackinaw from Fallen Leaf Lake (near Tahoe) had these objects in its stomach.  The objects are approximately 1 centimeter in diameter.  I have no idea what they could be.  Anyone have ideas?  Are there some crazy invertebrates living in Fallen Leaf Lake?

Whats the texture?

Whats the texture?

They didn't say.  I can ask.

Looks like a Sierra Nevada circular freshwater anenamee... Or its a snail

Mushroom.... Mac's will eat anything!

Maybe a dumb question, but its difficult to distinguish the texture/density from the photo ... are we sure that its fauna or is it possible that its plant material ? Maybe a mountain berry or a seed pod of some sort ? Did anyone happen to cut one open ? Fun little mystery.

I emailed the sender of the photo and asked if anyone had IDed the objects.  Here is his response:

"A few people have correctly identified the “mystery” objects as crayfish gastroliths. They are about 1 cm in diameter, hard and compressed when viewed laterally. They resemble mushromm buttons in shape. Jayne Brim-Box was the first to correctly identify them, perhaps because she works “down under”.

They are utilized as a calcium repository during periods when a crayfish is molting. See
http://museum.wa.gov.au/explore/blogs/aquatic-zoology/why-freshwater-crayfish-don-t-need-milk-healthy-bones
for a full explanation."

I never would've guessed!

Thanks for the update, Clayman. Very interesting !

Heres a good slide from a research project showing exactly what/where they are ...

That's really cool info all the way around, from crayfish physiology to the next step, dragging a creature bait across the bottom.