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SC/69B/SM/03
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Resource ID
22164
Access
Open
Document Number
SC/69B/SM/03
Full Title
ACOUSTIC MONITORING AND STATUS OF VAQUITA POPULATION IN 2023
Author
A.M Jaramillo Legorreta, E. Nieto Garc a, G. C rdenas Hinojosa And L. Rojas Bracho
Authors Summary
The population of vaquita has been declining for many years ago, as estimated by several works with data
gathered since 1993. It is the key factor considering the species as critically endangered. By 2018 it was
estimated that population was composed out of less than 20 individuals, using acoustic data to extrapolate
from an estimate of abundance in 2015. Along with abundance decreasing, it was also noted that
distribution area was also shrinking progressively, with acoustic activity now restricted to the Zero
Tolerance Area (ZTA). Given the importance of information about vaquita status, acoustic monitoring
was implemented in the ZTA in 2021. The effort was repeated in 2022 and 2023. Here we present the
data gathered for 2023. The sampling protocol included a 55 sites grid, from which some sites were
selected to sample along ten spring tide periods. A total of 46,204 hours of effort were applied in 43 sites
and identifying 208 acoustic encounters of vaquitas in 25 sites. The distribution of encounters shows that
the most used area is the western portion of the ZTA, with very low activity towards the east. A simple
model was used to estimate the rate of change of acoustic detection rate between consecutive years, using
a Bayesian approach. The rate of change between 2021 and 2022 was -6.3% (CI 95% -3.9% - +3.7%). For
the period 2022 to 2023 the rate of change was -20.7% (CI 95% -3.7% to -0.7%). The geometrical mean
for both rates of change was -14.4% (CI 95% -32.7% to +7.1%), with a probability of 91.5% that acoustic
detection rates declined. Between 2011 and 2018 it was estimated that acoustic detection rates declined
45% per year on average. If detection rate change inside ZTA is a proxy of population trend, vaquita
population keeps decreasing but at a greatly reduced rate (-45% to -14%). The acoustic monitoring
program for 2024 is already
Publisher
IWC
Publication Year
2024