Thursday, May 9, 2024

Who's the culprit?

  

This is a scene we came across after finishing field work this morning (9 May 2024).  Some empty-looking whelks (Nucella ostrina) on the sand...and upon closer inspection, their opercula nearby (the operculum is the "trap-door" on the bottom of a snail's foot that seals the opening to its shell when the snail is pulled in).

It looked like the snails had been eaten by a predator, but we couldn't recall seeing this before, so we looked around a little more.

We found even more evidence that something had been eating both whelks and limpets.  Here are a few examples, including snail shells and overturned limpet shells with most of the soft parts missing, but with a thin ring of tissue, evidence that they had been eaten recently:


 
So...who was responsible for eating these snails and limpets?
 
We weren't sure, but we kept looking, and Eric eventually spotted a clue.  Tracks in the sand around some of the predated shells:
 
 
After thinking through the possibilities, we're guessing these footprints might belong to a rat (!).
 
Rat predation on intertidal invertebrates has been documented previously (Thanks to Sergio!), but we don't recall seeing it locally before.  Maybe because there was a lot of sand at this site it was easier to notice the empty shells and the tracks in the sand.
 
Here's a close-up of one track in case anyone can help us with an identification.  The track was ~1 cm across.
 
 
You learn something new every day!

2 comments:

  1. Such an interesting find! I wonder if they're a bit small for rat tracks, though.

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  2. So curious to know what prints they are. Before seeing them, I would guess raccoons as I have seen them gleaning the beach at low tide. But the photos do not look to me to be either raccoon or rat. Opossum? Skunk?

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