Report of vaquita survey 2024
Gustavo Cárdenas-Hinojosa1, Armando Jaramillo-Legorreta1, Andrea Bonilla-Garzón2, Edwyna NietoGarcía1, Barbara L. Taylor3, Sarah Mesnick4, Annette Henry4, Núria Patiño-Sevillano2, Lorenzo RojasBracho5 Cormac Booth6, Len Thomas7
1 CONANP, Dirección Regional Península de Baja California y Pacífico Norte,
C/o CICESE, Camper 10, Carretera Ensenada-Tijuana 3918, Zona Playitas, Ensenada, BC 22860
2 Sea Shepherd Science Department, Sea Shepherd Conservation Society
3 Independent researcher
4 Southwest Fisheries Science Center, 8901 La Jolla Shores Drive, La Jolla, CA 92037
5 National Marine Mammal Foundation, 2240 Shelter Island Dr Ste 200, San Diego, CA
6 SMRU Consulting, St Andrews, Scotland
7 Centre for Research into Ecological and Environmental Modelling, University of St Andrews, St Andrews, Scotland
Executive Summary
Two ships (Seahorse and Sirena de la Noche), staffed with scientists whose combined experience studying marine mammals totaled around 400 years, surveyed the northern Gulf of California hoping to find and track vaquitas, the rarest marine mammal on earth. The search for these small elusive porpoises was aided by the efforts displayed by Mexican experts on acoustics supported by a group of local fishers to collect the acoustic data used to determine where vaquitas were spending time.
The study area comprised the Zero Tolerance Area (ZTA), the Extension Area (EA) and some other areas near the ZTA. The number of sightings was 9 in 2024 compared with 16 in 2023, and we recorded 70 acoustic encounters of vaquita compared with 61 in 2023. We caution that the reduced number of vaquitas detected within the ZTA does not necessarily indicate a decline in the species, because this zone represents a small area of the recent distribution of vaquita.
Using a method called Expert Elicitation, we found it very likely that no calves were seen, one yearling was seen, and there was a 75% probability that the total number of different individuals seen was between 6 and 8, with a 25% probability that between 9 and 11 individuals were seen. Since our search focused within the ZTA and the EA, 6-8 is considered a minimum estimate of the number of vaquitas left. The 2024 estimate is less than the estimated 8-13 seen in 2023 within a similar area All individuals sighted in 2024 appeared to be healthy.
As in earlier reports, we emphasize that because vaquitas move freely into and out of the ZTA, the number seen in the study area at the time of the survey should be considered a minimum.
Acoustic detectors were deployed at 34 sampling sites within the ZTA. Unfortunately, fourteen moorings with detectors were lost (five were recovered later) at the northwest of the ZTA where the acoustic activity of vaquita is higher. A trial with pop-up devices was conducted to determine whether they would eliminate the need for surface marking of the moorings. All moorings with detectors deployed with pop-up devices were successfully recovered and we recommend using these devices in future acoustic monitoring.
As in 2023, the period study of the survey was in May because the proportion of windy days was predicted to be less. On 15 days the winds were considered low enough to sight and track vaquitas; this compares with 10 days during the first May survey in 2023.Visual search effort focused on waters in and around the ZTA which is regarded as a stronghold for the last few vaquitas. Half of the 9 sightings in 2024 were outside the ZTA proper and inside the EA. Of the 9 sightings, 4 sightings were very brief and no photographs were obtained, and 3-4 of the long sightings were of the same pair of vaquitas. The final sighting was of 4 vaquitas, including the one-year-old, that were definitely not the pair identified in earlier sightings.
Figure 1 shows the tracklines of the two ships and the locations where vaquitas were seen. Acoustic research has consistently detected vaquitas along the northwestern edge of the ZTA (Figure 1). In 2023 vaquitas, including a mother and calf, were seen outside the ZTA in the area known as the Extension Area (EA). Because of these results obtained during the 2023 survey, additional concrete blocks with steel hooks were authorized for the protection of the EA in August 2023 (Figure 2).
Figure 1. Summary of vaquita acoustic and visual detections during the May 2024 survey. The ZTA is within the yellow corner dots. Corners of the Extension Area (EA) are indicated by red dots. Black dots are positions for survey navigation, some of which correspond to locations of acoustic detectors. Sites with acoustic detections are green dots. Sightings (purple dots) 3, 4, 5 and 7 were in the EA and sighting 6 was along the boundary of the ZTA. Tracklines of the Seahorse are in red and the Sirena de la Noche in blue. San Felipe harbor is the small square at the bottom of the figure.
Figure 2. Zero Tolerance Area and the Extension Area. San Felipe harbor is the small square at the bottom of the figure.
Seventeen local trainees were introduced to the visual-survey methods, and they observed from both ships. These trainees were enthusiastic, most saw vaquitas, and some could make a good future observer team with further training. We recommend that dedicated efforts be made by an experienced vaquita scientist to train this team. We also note that, due to the rarity of vaquitas, trainees would benefit from training in marine mammal observation and photography in La Paz or Ensenada and also from specific training in sighting porpoises in areas where porpoises are common, like British Columbia in Canada.
Although the ZTA appears to function as a sanctuary from gillnets, vaquitas may range outside this very small area to feed. Several patches of habitat used by vaquitas in the recent past have not been monitored since 2019. To accurately interpret the present results and provide a more reliable assessment of the vaquita’s conservation status and distribution, we recommend that an acoustic research program be undertaken in other areas of known or suspected vaquita habitat this summer.
