Decline towards extinction of Mexico's vaquita porpoise (Phocoena sinus).

Armando M Jaramillo-Legorreta,Jay Barlow,Edwyna Nieto-Garcia,Gustavo Cardenas-Hinojosa,Barbara Taylor,Len Thomas,Lorenzo Rojas-Bracho,Jeffrey Moore,Nicholas Tregenza,Jay M Ver Hoef

doi:10.1098/rsos.190598

Abstract

The vaquita (Phocoena sinus) is a small porpoise endemic to Mexico. It is listed by IUCN as Critically Endangered because of unsustainable levels of bycatch in gillnets. The population has been monitored with passive acoustic detectors every summer from 2011 to 2018; here we report results for 2017 and 2018. We combine the acoustic trends with an independent estimate of population size from 2015, and visual observations of at least seven animals in 2017 and six in 2018. Despite adoption of an emergency gillnet ban in May 2015, the estimated rate of decline remains extremely high: 48% decline in 2017 (95% Bayesian credible interval (CRI) 78% decline to 9% increase) and 47% in 2018 (95% CRI 80% decline to 13% increase). Estimated total population decline since 2011 is 98.6%, with greater than 99% probability the decline is greater than 33% yr−1. We estimate fewer than 19 vaquitas remained as of summer 2018 (posterior mean 9, median 8, 95% CRI 6–19). From March 2016 to March 2019, 10 dead vaquitas killed in gillnets were found. The ongoing presence of illegal gillnets despite the emergency ban continues to drive the vaquita towards extinction. Immediate management action is required if the species is to be saved.

Highlights

The vaquita (Phocoena sinus) is a species of porpoise endemic to the northern Gulf of California, Mexico
Acoustic data were sometimes missing during this period because of logger failure or loss; this could potentially bias annual trend estimates if there is a temporal trend within a monitoring period in instrument loss and in acoustic detection rate
From the acoustic data alone, using the statistical models, the estimated decline in detection rate since monitoring started in 2011 is 99%. This estimate should be more reliable than a raw count, because it corrects for missing data, the change in raw acoustic detection rate is remarkably similar: an average of 4.37 clicks were detected per sensor per day of monitoring in 2011, and 0.052 in 2018, a decline of 99%

Summary

Introduction

The vaquita (Phocoena sinus) is a species of porpoise endemic to the northern Gulf of California, Mexico. Since about 2010, an illegal gillnet fishery for an endangered fish, the totoaba (Totoaba macdonaldi), has resurged throughout the vaquita’s range. While vaquitas are difficult and expensive to survey visually, they are readily detectable using acoustics because they produce a nearly continuous series of echolocation clicks. This makes them excellent candidates for passive acoustic monitoring to estimate trends in abundance. Based on preliminary results through 2014, the government of Mexico enacted in 2015 an emergency 2-year ban on gillnets throughout the species’ range to prevent extinction, at a cost of US$74 million to compensate fishers [2]

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Conclusion