Researchers with the Marine Mammal Energetics and Nutrition (MMEAN) lab are looking forward to continuing their work with marine mammals at the Vancouver Aquarium, even though access to lab facilities and animals in the aquarium’s care has been limited due to the COVID-19 pandemic.
Despite these setbacks, members of the MMEAN lab team produced two recent publications that appeared in The Canadian Journal of Zoology and Marine Mammal Science.
Northern fur seals
The study’s findings have implications for northern fur seal survival rates. Individuals within this species tend to specialize in their diets, with some foraging on food that is more fat-heavy and thus more beneficial to maintaining their health, while others feed on less ideal types of fish.
“If they eat food item A, then they have to eat 7 per cent more than if they’re eating food item B. That may not make a difference for most of the population, but when times get tough, especially for the animals in the population that are barely making it, that might make a huge difference in survival at the population level,” said David Rosen, an assistant professor at the Institute for the Oceans and Fisheries (IOF) and principal investigator of the MMEAN lab.
Rosen also led another recently published study on two juvenile walruses sent to the Vancouver Aquarium from Quebec. Rosen measured the resting metabolic rate (the rate at which an animal burns calories when not moving) and underwater swimming metabolism of the two Walruses. To get these measurements, Rosen and the Vancouver Aquarium training staff spent days coaxing the walruses to swim and then rest inside a chamber that measured the animals’ oxygen consumption. One surprising discovery: the young walruses had resting metabolic rates closer to those seen in adult marine mammals – an indication that walruses expend less energy when resting than researchers might expect.
Dr. David Rosen
“The resting metabolic rate doesn’t take up too much energy. However, that is vastly overshadowed by how much energy they expend swimming,” Rosen said.
Walruses typically stay near their food sources — places like clam beds, for example. However, the ice that they rest on when they reach these food sources is melting, meaning that they are having to travel greater distances to eat.
“They still have to go to those foraging beds and they still have to haul out on that ice. So, it becomes further and further away that they have to do this. There’s no real way to offset that cost. It’s kind of a vicious circle, because they need to swim further to get that food, but they also need more of that food because they’re swimming further,” Rosen said.
Staying busy outside the lab
Rhea Storlund, a PhD student working in the MMEAN lab, has been away from the Vancouver Aquarium since March when COVID-19 caused research to shut down.
However, distance from the aquarium gave Storlund time to collaborate with a group of undergraduate engineering students to begin building an “inflation testing rig.” The device mimics the flow of blood through the heart and circulatory system of marine mammals, allowing Storlund to see up close the unique characteristics of the organ as it beats and pulses. This project has been temporarily put on hold.
When she returns to the aquarium, Storlund hopes to test whether sea lions can consciously control their heart rates when they spend long periods of time underwater. She will use an echocardiogram (a device that produces an image of the heart using sound waves) to measure the sea lions’ heart rates while they do “trick dives” – a dive where the trainer prompts the sea lion to stay underwater longer than it expects before the trainer calls it back to the surface.
The research is important in helping to understand how well marine mammals can survive in changing habitats.
“If these animals are limited by how low their heart-rate can go, that affects how long they can stay underwater, which in turn has effects on what they can do in the wild, and where they can forage,” Storlund said.
On the horizon
With COVID-19 restrictions making travel to locations like Alaska more difficult, Rosen said that he plans to expand local field work.
“Vancouver is a really interesting place because we love our nature, but we also love our development, so we’re getting a couple studies off the ground looking at what that urbanization means to our local marine mammal populations,” Rosen said.
Additionally, he hopes to explore surprising marine mammal behaviours that researchers have been observing in the wild near Vancouver, like the re-emergence of certain dolphin populations and transient killer whales entering Vancouver waterways.
Although the COVID-19 pandemic has created limitations for scientists doing research in every field, Rosen remains optimistic:
“It just means we have to be creative to keep research going.”
Tags: British Columbia, David Rosen, Faculty, IOF students, Marine mammals, MMean Lab, Research, sea lions, seals