I received a reply to my query to the TPWD Extension Wildlife Biologist in Hidalgo County, the county in which Mercedes is located:

Hi Ben,

Thanks for the email. Unfortunately, I am of little help. I have not heard of anyone with photos of a jaguar or heard of any verifiable jaguar sightings here in the Lower Rio Grande Valley. I'm sorry I can't be more help than this.

Best,
Tony

I'm out of here.

Ben

Some days it takes most of the day for me to do practically nothing...