A new abundance estimate for vaquitas: first step for recovery

Summary

A three-boat line-transect survey in summer 1997 was the first designed to estimate vaquita abundance over the whole range. It recorded 125 sightings of vaquita groups and estimated a total population of 567 animals (95% CI 177 to 1,073). The authors say this is better than earlier estimates, but that it should not be compared directly with the 1993 figure.

Why it matters

It is the first complete estimate of the vaquita population, and later surveys use it as the reference point for measuring decline.

Key findings

1. 01 Total population estimated at 567 animals, 95% CI 177 to 1,073.
2. 02 125 sightings of vaquita groups, mainly because large binoculars were seven times more effective than hand-held binoculars.
3. 03 The vaquita's range is restricted to the northwestern corner of the Gulf of California.
4. 04 The boundaries of the Upper Gulf of California and Colorado River Delta Biosphere Reserve do not match the vaquita's distribution well.
5. 05 The shallow area north of San Felipe held a higher density of animals than earlier surveys indicated.

Caveats

The 1997 estimate was more than twice the 1993 estimate, but the authors state that several reasons prevent a direct comparison and that it should not be concluded the population is increasing. The confidence interval is wide, spanning 177 to 1,073.