Authorities found 300 dead sharks on a roadside in Michocán on Tuesday, some 240 kilometers from the sea.
The shark carcasses, gutted and missing their fins, were found near Yurécuaro.
Residents of the community of Monteleón alerted authorities that there were multiple white sacks at the edge of the Piedad-Yurécuaro highway. Initially residents believed they contained human remains, a more common sight on Mexican roadsides than dead sharks.
Environmental protection officials believe the fish, called thresher sharks, were caught in Sonora and Sinaloa and were being transported to Mexico City.
But it appears that thieves hijacked the vehicle while it was en route and tossed out the sharks.
Thresher sharks are fished for their meat, liver oil, skin and fins, which are used in shark-fin soup.
They are not a protected species in Mexico but they are listed as vulnerable to extinction by the World Conservation Union.