Excerpts below from the websites https://en.wikipedia.org/wiki/Vaquita#Primary_threats and https://www.worldwildlife.org/species/vaquita
The vaquita (Phocoena sinus), the world’s most rare marine mammal, is on the edge of extinction. This little porpoise wasn’t discovered until 1958 and half a century later, we are on the brink of losing them forever. Vaquitas are often caught and drowned in gillnets used by illegal fishing operations in marine protected areas within Mexico’s Gulf of California. The population has dropped drastically in the last few years. These creatures are critically endangered, with only 12 left in the world.
The vaquita has a large dark ring around its eyes and dark patches on its lips that form a thin line from the mouth to the pectoral fins. Its dorsal surface is dark gray, sides pale gray and ventral surface white with long, light gray markings. Newborn vaquitas have darker coloration and a wide gray fringe of color that runs from the head to the dorsal flukes, passing through the dorsal and pectoral fins. They are most often found close to shore in the Gulf’s shallow waters, although they quickly swim away if a boat approaches.
Vaquitas tend to forage near lagoons. All of the 17 fish species found in vaquita stomachs can be classified as species inhabiting relatively shallow water in the upper Gulf of California. Vaquitas appear to be rather non-selective feeders on crustaceans, small fish, octopuses and squid in this area. Some of the most common prey are teleosts (fish with bony skeletons) such as grunts, croakers, and sea trout. Like other cetaceans, vaquitas may use echolocation to locate prey, particularly as their habitat is often turbid.
Accidental drowning in gillnets set by fishermen meant for catching the totoaba fish is the primary cause of incidental mortality for the vaquita. Three fishing villages in the northern Gulf of California are primarily involved in the totoaba fishery and, as a result, most directly involved in threats to the vaquita. San Felipe, in Baja California, and Golfo de Santa Clara and Puerto Peñasco, in Sonora, has a total population of approximately 61,000. Up to 80% of the economy in these towns is associated with the fishing industry. A total of 1771 vessels make up the artisanal fleet that has permits to fish with nets, with the total size of the commercial fishery unknown due to the extent of the black market for totoaba. Around 3,000 individuals are involved in the totoaba industry overall. The total economic impact of the industry for the region is estimated to be approximately $5.4 million USD annually, or $78.5 million Pesos. Socioeconomic surveys of the northern Gulf have suggested that approximately $25 million if invested in the region through education, equipment buyout, and job placement, could end the vaquita bycatch problem.