Mexican authorities have caught three boats shrimping in a refuge for the endangered vaquita marina, the world's smallest porpoise.

Mexico's environmental protection agency says the boats belonged to fishermen in the town of Golfo de Santa Clara, at the northern edge of the Sea of Cortez.

It said Tuesday that the three people detained also face sanctions for violating a Jan. 15 fishing ban for the broader region due to red tide, an algal bloom phenomenon that can be toxic to human health.

The vaquita marina is native to the Sea of Cortez and can reach about 5 feet (1.5 meters) in length. The porpoise is critically threatened by illegal gillnet fishing, and experts say fewer than 100 remain.

Mexico recently began using unmanned drones to patrol the vaquita's habitat.