New estimate of vaquita status improved through elicitation of expert knowledge

A vaquita being tracked within the Zero Tolerance Area and a panga with a buoy for a set gillnet in the background on 17th October 2019. Credit. Todd Pusser. 

The results of a virtual workshop to use expert elicitation to better estimate the number of vaquitas seen in the Zero Tolerance Area are now available here (Final Vaquita Expert Elicitation Report).  Since 2019 acoustic monitoring to assess trends in abundance of the vaquita has not been possible because so much equipment has been stolen.  With so few vaquitas remaining, a two-ship effort in October 2019 was launched in the hope of obtaining sufficient photographically identified vaquita individuals to use mark-recapture methods to estimate vaquita numbers.  Although there were 7 encounters with vaquita groups, surviving vaquitas are so wary and hard to approach that insufficient numbers of high-quality photographs were obtained for the analysis. Therefore, a new approach was adopted, utilizing expert elicitation to obtain the best available estimate of the number of vaquitas seen.  A workshop was held in August, 2020 and included all observers who participated in the vessel-based field survey in October 2019, and was led by researchers at St. Andrews University.  The results of the expert elicitation exercise found the mean estimate for the number of vaquita calves seen was 3 with a 63% belief that there were at least 3 calves.  The mean estimate for the number of unique vaquitas seen in all 7 sightings was 9.4 with a 40% belief that there were at least 10.  Also of note was that tracking vaquitas was difficult because the ships and pangas had to maneuver around illegal fishers with gillnets set.

A female vaquita and her calf next to a panga with a gillnet being set within the Zero Tolerance Area on 17th October 2019. Credit: Museo de la Ballena