Summary
This paper gives the first abundance estimates for the vaquita, drawn from four boat, aerial and ship surveys carried out in Mexico between 1986 and 1993. The four estimates range from 224 to 885 animals and are all very imprecise, because the surveys had few sightings and borrowed some inputs from the harbour porpoise. The authors concluded that every estimate put the species at a critically low level.
Why it matters
It is the earliest numerical estimate of how many vaquitas exist, and it is the 1993 ship-survey figure of 224 that later papers set beside the 1997 full-range estimate.
Key findings
- 1986-1988 boat surveys: 503 animals (CV = 0.63).
- 1988-1989 aerial surveys: 885 animals (CV = 0.50).
- 1991 aerial survey: 572 animals (CV = 1.43).
- 1993 ship survey: 224 animals (CV = 0.39).
- Weighted log-linear regression, 1986 to 1993: change of -17.7% per year (95% CI -43.2% to +19.3%).
Caveats
The four surveys used different methods and did not all cover the whole range, and some parameters came from the harbour porpoise, so the estimates are not directly comparable with each other or with the 1997 full-range survey. The confidence interval on the trend runs from a 43.2% yearly decline to a 19.3% yearly increase, so the paper does not establish a decline on its own.