By Diane Claridge, PhD and Charlotte Dunn, PhD:
Turns out that’s a difficult question to answer. Beaked whales feed at more than ½ mile down and are fairly skittish critters while near the surface, and weighing in at over a ton means catching, measuring, and releasing is certainly not an option! Besides, perhaps a more important question is, who cares how big these whales are? Well, the U.S. Navy, that’s who.
Unfortunately for beaked whales, their deep-diving behavior means they share waters with Navy submarines, and when the Navy uses powerful sonar during training exercises, beaked whales are affected. Recent studies at the U.S. Navy’s Atlantic Test and Evaluation Center (AUTEC), off Andros Island in The Bahamas, indicate that Blainville’s beaked whales move away from sonar when they hear it. We believe this movement is displacing whales from their preferred feeding areas and are concerned this will compromise the animals’ body condition, which will impact their survival and reproduction success. And that’s why size matters.
With funding from the U.S. Office of Naval Research, the Bahamas Marine Mammal Research Organisation (BMMRO) and NOAA Fisheries, we conducted a feasibility study to test whether a drone could be used to measure length and girth of beaked whales. Using length, we can monitor growth as animals mature, while girth measurements tell us if an animal is pregnant, and if so, we can monitor if the calf survives. Based in Sandy Point, off the southwest coast of Abaco Island, BMMRO has been studying beaked whales for 25 years and knows these whales individually: how old they are, what sex they are, how many offspring they have had, etc. So, Abaco was the ideal place to try to get measurements of whales of known age and current reproductive state.
From our Novurania 680DL rigid-hulled inflatable, our science team deployed a small APH-22 marine hexacopter named “Goose” with a camera attached to obtain vertical images from 100 feet above beaked whales. During 30 flights over the 2-week study, “Goose” successfully photographed 10 different beaked whales. So, we now had images in hand of males and females, both young and old, as well as females with and without calves.
So… How big is a beaked whale? Blainville’s beaked whales ranged in length from the smallest calf measuring 9 feet to the largest adult at 14 feet. The girth of one female seen without a calf was notably larger than the other females, and we predicted she was pregnant. Three months after the study ended, we saw her again with a newborn calf!
With the success of our feasibility study, plans are to apply this approach to measure the length of beaked whales at AUTEC and monitor pregnancies to determine if displacement from sonar is causing nutritional stress and affecting reproductive success. It is the responsibility of the U.S. Navy and the science community to effectively monitor populations that are being impacted to affect change when needed. This study serves an example of that process in action.
The authors are research biologists with the Bahamas Marine Mammal Research Organisation. Follow the organization’s work at http://www.bahamaswhales.org and also on Facebook, Instagram and Twitter.