UBC study analyzes the movements and dives of Hudson Bay ringed seals

Being a part of the Arctic food web means constantly moving around trying to avoid being eaten while looking for a snack yourself. This Q&A with Katie Florko, IOF PhD student, tells us more.

Observations of Hudson Bay ringed seals may lead to a better understanding of the correlation between foraging behaviour and prey density. A new UBC study tested the assumption that predators change their movement and behaviour according to the density of their preferred prey. Using satellites to detect the horizontal movement and dives of Hudson Bay ringed seals, a not-so picky, common predator in the Arctic waters this was explored.

Hudson Bay ringed seals, identified by small ring shapes scattered across their backs, are the most common pinniped in the Arctic. These furry mammals play an important role in the northern region by being an intermediary in the food chain where they are favoured prey for polar bears. They are also generalist predators, choosing to forage on any locally available prey, including Arctic cod, northern sand lance, capelin, and various invertebrates.

This makes them the perfect mammal to follow around the chilly waters of the Arctic.

We sat down to talk to Katie Florko, lead author of the study and a PhD student in the Statistical Ecology Research Unit at UBC’s Institute for the Oceans and Fisheries.

Why did you analyze the movement and behaviour of these Hudson Bay ringed seals?

The motivation for this one was actually from a previous chapter of my thesis, which looked at changes in fish distribution in the area. It turned out that fish we were looking at were the primary prey of ringed seals, so we did a big projection study, where we looked at what the future will look like for ringed seal prey in Hudson Bay. We made a bunch of maps of the differences in fish that we’d expect to see, the space, size, quantity, species composition, and all these kinds of things.

What we found was this really big shift where the previous main species of fish prey, the Arctic cod, that was normally well-distributed, was retracting northwards, and all of these more temperate species were coming in. These more temperate species have a lower energetic food value, which means that there would be a bunch of consequences for fish. So, with this chapter, we looked at what this means for the ringed seals.

What are the changes happening with the fish?

There is reduced Arctic cod throughout the study area in Hudson Bay, and they appear to be moving north. It could be for a variety of reasons: environmental conditions; temperature; sea ice; salinity; pH; or even amount of oxygen in the water.

The new species coming in, they have, historically, always been in the area, but they are becoming a lot more prevalent, and they’re really increasing in the southern and coastal areas. These species are typically smaller, which means they have less food energy content. So, one Arctic cod equals a lot more of these little fish. This impacts the ringed seals.

How did you track the movements and behaviours of these seals?

We matched up the movement of the seals to the different fish that we had, and saw which areas they were using and what behaviours they were undertaking in different areas. We validated these models with diving behaviour, and also used what we call time depth recorders on the seals, so we could measure their dives. This provided us with all kinds of information.

What did you find?

What we found was kind of confusing. We typically use movement data where there is an area restricted search. This is where the movement of the animals becomes really convoluted: they’re turning angles with shorter, lower speeds. Historically, studies that used movement data assumed that area restricted search meant there was prey in that area. This means foraging for the seals. We took that apart using these prey layers and the ring seal movement and diving behaviour.

What we found was that it’s not always the case where area restricted search means more prey. And neither was diving behaviour. So, our study highlighted that these things are really complex, and we don’t know a whole lot about what ringed seals are actually doing.

What are you doing next?

We’ll have to talk again in a couple of months, because my next chapter incorporates polar bears as well. It turns out that when you look at like ringed seal movement with prey, there’s no relationship, it doesn’t make sense. But if you add in polar bears, it shows a super, crystal-clear pattern where the seals are avoiding prey because of predators or selecting for prey. They’re making compromises based on how risky their environment is. It’s really interesting.
 

Linking movement and dive data to prey distribution models: new insights in foraging behaviour and potential pitfalls of movement analyses was published in Movement Ecology.

Tags: Arctic, IOF students, pinnipeds, Research, seals, SERG, statistical ecology