Researchers combine visual surveys and passive acoustic monitoring to estimate the dwindling vaquita population, but despite their best efforts, pinpointing an exact number remains an ongoing challenge.
Their elusive nature and aversion to human contact make studying vaquita exceptionally difficult. In response, researchers have adopted a two-pronged approach, combining visual surveys and passive acoustic monitoring (PAM), to gather vital information about their presence and distribution in the hopes of better understanding and conserving the species.
Visual surveys are an important component. These surveys involve teams of trained observers stationed on boats, scanning the surface of the Sea of Cortez with large binoculars (“big eyes”) or high-powered cameras, searching for any signs of the vaquita. To increase the chances of sightings, visual surveys are typically conducted during the calmest weather and sea conditions. However, the vaquita’s shy nature and tendency to avoid boats make direct encounters rare. As a result, visual surveys can be time-consuming and require tremendous patience from the researchers. Despite these challenges, visual surveys remain essential, providing valuable sightings and photographic evidence that can help assess the vaquita’s population structure, habitat use, and individual behavior.
Passive Acoustic Monitoring
To complement visual surveys, researchers deploy passive acoustic monitoring (PAM) to detect the vaquita’s presence through their natural communication and navigation methods. Vaquitas, like other cetaceans, rely on echolocation to navigate their environment and locate prey. They emit high-frequency clicks that bounce off objects and return to the vaquita, providing vital information about their surroundings. By using underwater microphones, or hydrophones, strategically placed throughout the vaquita’s preferred habitat, scientists can detect these echolocation clicks and analyze their frequency and distribution. PAM offers a less invasive and more continuous method of monitoring the vaquita’s presence, as it can operate 24/7 and is less affected by weather conditions compared to visual surveys.
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Both visual surveys and PAM face unique challenges, however. Visual surveys are limited by the vaquita’s elusive behavior, visibility issues caused by surface conditions, and the dependency on favorable weather. Additionally, visual surveys can be expensive and logistically demanding due to the need for specialized equipment and trained observers. PAM, on the other hand, is constrained by the need for vaquitas to vocalize or echolocate during the monitoring period, potentially overlooking individuals. Furthermore, PAM’s effectiveness can be impacted by the presence of other marine mammals, anthropogenic noise, or technical issues with the hydrophones.
Given the inherent limitations of both methods, researchers cannot provide an exact count of the remaining vaquitas. Instead, they offer population estimates in the form of ranges, which account for the uncertainties and inaccuracies of the detection methods. These ranges reflect the minimum and maximum number of vaquitas that may be present, given the collected data. As the vaquita population continues to decline, the accuracy of these estimates becomes increasingly uncertain, emphasizing the urgent need for more effective conservation measures.