Areal photogrammetry for an index of whale condition
Drones are now being flown above the waters of Southeast Alaska and not for Amazon or pizza delivery (to use Andy’s favorite joke). More incredibly, these drones are being used to measure the size and health of individual whales in the wild. This is important because scientists from Southeast Alaska have noticed a few troubling observations in the last few years which they hope to shed some light on. Firstly, recent observations suggest there are fewer cow and calf pairs returning in summer. Secondly, less whales are migrating away from summer feeding grounds in winter, essentially staying in Southeast Alaska all year. This leads to questions surrounding the health of the population and if the whales are getting enough food to migrate and breed. In launching the drones, we will begin to find the answers to these questions.
Droning a playful humpback. Pectoral flippers can be 5m long so can make quite a bang on the water. Image under permit 19703
This project is in its first year of in collaboration with the University of Hawaii to study the heath of the Humpback whale population here in Southeast Alaska. Why Hawaii you may ask? Well as it turns out 95% of the whales here belong to the breeding grounds in the Hawaiian Islands and so working together will hopefully give a picture of the body condition of a whale throughout the entire year. To understand why the condition of a whale will change over the year, I will briefly describe how whales are divided by breeding strategy.
The whales of the infraorder Cetacea are split into two categorys Mysticeti (baleen whales, large filter feeders like humpbacks) and Odontoceti (toothed, echolocating whales like sperm whales). Typically, this division also splits Cetacea into two different breeding regimes. Capital breeders (most baleen whales) and income breeders (toothed whales). Capital breeders store energy for reproduction, migration and survival, while income breeders use acquired energy on a continuous basis including during reproduction.
Diving together multiple whales can be measured at once. Image under permit 19703
Humpback whales are capital breeders, they spend half the year feeding, layering on the fat and muscle so they are big enough to make the trip to the breeding ground and back. Once they leave the summer feeding grounds, they will not eat until they return next summer. Humpback whales undertake one of the longest migrations in the animal kingdom. These whales typically travel more than 5000 km from their summer feeding grounds to their winter breeding grounds. Imagine how much gas needs to be in the tank for a trip that long and strenuous, and even more if you have to support a calf.
Cows who give birth will lose up to 30% of body mass during the migration. Using aerial photogrammetry, it has been shown that female humpback whales can lose lose up to 3cm every other day to the milk required to feed a growing calf. This extreme energetic cost could be the reason why some animals are not leaving the feeding grounds. As they know if they get pregnant they don’t have the size to be able to support a calf. Scientists can now measure the same cows throughout the feeding season, tracking their body condition until late season when most whales begin their migration to the breeding grounds. It may then be possible to detect potential differences in body condition between cows that are leaving to breed and those that are choosing to stay in the feeding grounds all year round. As you can now see this photogrammetry is pretty powerful stuff, so the best team and gear has been brought in to measure the whales of Southeast Alaska.
Size matters! To survive the breeding season animals have to have enough fat stores for up to 5 months of fasting. Image under permit 19703
Martin van Aswegen is the certified drone pilot in charge of capturing this data as well some epic footage of bubble nets and breaching whales, no pressure! Martin is flying the new DJI inspire 2 drone, some impressive specs include; a top speed of almost 100km/h! A laser altimeter reporting its altitude 20 times per second and it’s equipped with 21 mega pixel camera capable of shooting super high resolution 4K. The Drone has a 20min flight time and flying from a boat as we typically do, comes with some challenges. Wind and waves can make landing the drone on the boat challenging (as we saw when Andy’s drone went for a swim…). So it’s now required that someone has to launch and catch the drone from the back of the boat. Said person has to wear a helmet, goggles and gloves as the props spin at roughly 10,000 RPM and can do some serious damage to anything that it comes in contact with!
The DJI inspire 2
Aerial photogrammetry has revolutionized non-invasive measurements of whales, and has only been happening for about ten years. Previously, it was only possible to get these measurements from dead whales or from whaling data which was not particularly accurate. So drones have really changed the game. To get these measurements, the drone must be directly above whale so images can be linked with the known range finder altitude. As we also know the focal length of the camera, it gives a measure of pixels which can be converted into absolute length of the whale.
A perfect day gives beautiful measurement photos. Image under permit 19703
Measurements are taken from the rostrum (front tip of the whale) to the tail fork, giving an estimate of total body length. Measurements of the width are taken at 5% increments, totalling 20 measurements along the body. These lengths then can be modelled into volume and an index of health.
The summer field season is almost over here in Baranof Warm Springs and we have approximately 100 individual whale images. The aim of this project now is to return to measure whales again in the fall and winter to look at the condition of the whales who do not migrate. This exciting research has just begun but has already give us some novel insights into the life of a Southeast Alaskan Humpback.