How much food does a dolphin need to eat? No it isn’t a riddle, but a question driving an exciting new study by UBC Masters student Erin Rechsteiner. As documented in earlier Wild Whales posts, for much of the 20th century Pacific white-sided dolphins were thought to be an open-ocean species. However, in the mid-1980s groups of dolphins began appearing in the inshore waters of British Columbia, and in the last decade even further south into the Strait of Georgia, including Howe Sound recently! With dolphins now spending time in these areas, questions about their role in the ecosystem and interactions with the food web have been raised. With the help of animals at the Vancouver Aquarium and in the wild, Erin hopes to begin understanding the energetic demands of this feisty species which will better help researchers comprehend their needs and interactions with their environment.
But how do you figure out how much a wild dolphin needs to eat? It isn’t easy! To start, Erin will be working with the three rescued, but non-releasable Pacific white-sided dolphins that reside at the Vancouver Aquarium. These three dolphins are being trained to surface and rest in a metabolic dome, a bubble that sits on the water. By measuring their respirations in this dome, scientists can extrapolate their resting metabolic rate- essentially the number of calories an animal needs just for basic body functions while at rest. This is a standard rate, constant between both wild animals and animals that live in Aquariums.
From this resting metabolic rate, Erin can determine the minimum number of calories a dolphin would need. But of course, dolphins in the wild need much more than the minimum- this active, speedy species needs a lot of fuel! To begin estimating these ‘in-the-wild’ caloric needs, Erin hopes to establish an activity budget and average swimming speeds for wild dolphins. That is, how much time, on average, do they spend resting, foraging, traveling, milling and socializing, and how fast they swim in each activity state? Once she knows the answers to these questions, she can figure out how many calories they expend in each activity state. This is similar to the way humans know how many calories are burned in an hour of jogging, if you jog at a speed of 10km/hr. Erin is spending part of this summer in the Strait of Georgia around Nanaimo and surrounding area, studying wild Pacific white-sided dolphins to answer those questions.
Once Erin estimates the calories needed by a dolphin for an average day, it may be possible to determine how many fish it would take to sustain the animal. Of course, understanding their diets is essential in this step. What do dolphins eat? How many of each different type of fish? Previous studies have shown that while inshore dolphins focus on forage fish, but while offshore, their diet seems to be high in squid. This information, combined with Erin’s findings on the PWSD’s caloric needs, will lay the groundwork for researchers to better understand the role Pacific white-sided dolphins play in the coastal food web.
Want to help Erin with her research? She needs to know where the dolphins are in order to study their activity. You can help her by reporting your sightings of Pacific white-sided dolphin in and around Nanaimo and neighbouring waters to the B.C. Cetacean Sightings Network. We will be communicating these sightings to Erin to help her with her field work. Report your sightings in ‘real time’ by calling 1.866.I.SAW.ONE or report online here.