Summary
This paper gives the last estimate of the whole vaquita population, for 2018, about 9 animals (95% credible interval 6 to 19). It combines eight years of acoustic monitoring (2011 to 2018) with the 2015 survey estimate and with minimum counts of animals seen in 2017 and 2018. The authors also revise the 2015 estimate upward, from a posterior mean of about 60 to 100.
Why it matters
It is the most recent estimate of total vaquita numbers, and it shows the decline continuing at a very high rate after the emergency gillnet suspension of 2015. Every survey since has counted the animals seen in a small area instead.
Key findings
- 2018 population estimate: posterior mean 9, median 8, 95% credible interval 6 to 19.
- Decline of 48% in 2017 and 47% in 2018, each with a 95% credible interval that runs from a steep fall to a small rise.
- Total decline since 2011 is estimated at 98.6%, with greater than 99% probability that the decline exceeds 33% per year.
- The 2015 estimate is revised to a posterior mean of 100 (median 93, 95% credible interval 47 to 191), up from the earlier figure of about 60.
- From March 2016 to March 2019, 10 dead vaquitas killed in gillnets were found.
Caveats
The 2018 figure is a model projection from the 2015 survey, shaped by the acoustic trend and by the minimum counts of 7 (2017) and 6 (2018) animals, so its credible interval is wide. The paper describes the estimate as for summer 2018 in the abstract and autumn 2018 in section 3.3. Later surveys counted more animals than this estimate projected (Rojas-Bracho et al. 2022).
Original abstract English
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.