The vaquita (Phocoena sinus) is the most critically endangered cetacean species in the world and is a small porpoise endemic to the northern Gulf of California, Mexico. As fishing efforts increased greatly, over half of the species population was lost in 11 years. Gillnets for shrimp cause very high rates of by-catch, thus incidental mortality is the principal threat for vaquita survival. We estimated the current fishing effort in the Upper Gulf of California in order to estimate vaquita by-catch mortality. Fishing activities carried out by artisanal fishermen in the Port of San Felipe were monitored from September 15 – December 14, 2013 and from October 17 – October 21, 2013 in El Golfo de Santa Clara. Information on the number of pangas fishing was collected daily. Since every boat goes out and back once per day, we consider the number of trips as our measure of fishing effort. A total of 5,505 trips were observed during the sample period. Using Bayesian analysis, we estimated the fishing effort for the days that were not monitored to cover the entire shrimp season. A total of 50,692 trips were estimated using the Markov Chain Monte Carlo. We estimated the mortality rate per trip using the fishing effort estimation and available demographic information of the vaquita population. The mortality rate of the vaquita resulted in 3.15×10-6 trips-1. By 2014, the estimate of current vaquita abundance was 97 individuals and using the number of fishing trips estimated per day, we estimated 28 vaquitas caught in artisanal nets for the 2013-2014 period. With this amount of fishing effort and lack of enforcement, unless drastic action is taken, the vaquita will be lost.