With the help of some locals….

By Lars Boehme (University of St Andrews) and Gui Bortolotto (University of Aberystwyth)

One tool PICCOLO has in its toolbox is a so-called seal tag. The real name is Satellite-Relay-Data-Logger or SRDL. We also have them in different versions on board, some have “only’ a miniature CTD (for Temperature, Salinity and Depth), others also record Fluorescence, Oxygen or Light levels. As the name suggests, these loggers or tags are deployed on seals (Figure 1).

Figure 1: Male Southern Elephant seal equipped with an oxygen and CTD tag (Photo by G Bortolotto).

An oceanographic measurement from the SDA can tell us a lot about that one specific location (see the “How do we measure what the ocean water is like several kilometres below the ship?” blog), but what does the ocean in Antarctica look like in the winter, when it is practically impossible for ships to sail in the area, and are our measurements really representative? The tagged seals spread out and provide data from places that we have not visited. The tags stay on until the next yearly moult, so we hope to get data until the end of this year.

Lars Boehme and Gui Bortolotto are the seal scientists onboard. They had to secure multiple permits and go through ethics reviews before they could tag any animals. Tagging these seals serves two purposes: The data collected paints a picture of the oceanographic conditions in the western Weddell Sea, but also records the seal’s behaviour to understand how these charismatic animals live in this harsh (for us) environment.

Lars and Gui tagged 2 Southern Elephant seals, 6 Crabeater seals and 11 Weddell seals during the PICCOLO cruise. The spread across species helps us to look at the different behaviours of these top predators in this region as they find their own niches in the ecosystem.

How do you catch a seal?

There are many different ways of catching a seal. The method depends on the species, but also the situation the seal is in. On this cruise, we used two ways, the first utilized the use of a blowpipe and dart and the second constraining the seal in a bag (Figure 2) and then anaesthetizing them using a syringe and needle (similar to an epidural). The whole process of anaesthetizing the seal, taking biological measurements (like length and girth), attaching the tag to making sure that the seal is properly awake again takes about 30 minutes.

Figure 2: Gui Bortolotto using eye drops on a Weddell seal, which was caught in a head bag. (photo by Lars Boehme)

What kind of data do we get?

We get two types of data using the tags. We get data, which describes the physical environment like temperature, salinity and oxygen, and we get information about how the animals behave like where they go and how long and deep they dive.

The environmental data can be treated like coming from a ship as we get the information along the seal’s track from the surface of the ocean to the depths they dive to (Figure 3). We can then analyse it and use it in conjunction with all the other data sources we have.

Figure 3: A temperature section collected by one of the tagged seals showing some warmer water at depth. (image by Lars Boehme)

The behavioural data has many different forms. The first information we get are the seal locations (Figure 4). While this seems to be very rudimentary data, it is very important as it can help us to distinguish hotspots for the different species and how they find their own niches or how their living space overlaps.

Figure 4: A map of the northeastern side of the Antarctic Peninsula. The dots mark locations from the tagged seals. Weddell seals are in red, Southern elephant seal are in green and Crabeater seals are in yellow. (map by Lars Boehme)

The future

While the PICCOLO cruise is coming to an end, the data collection will go on. The seals will send us daily updates on where they go and what they are up to. Even better, they will provide us with more environmental information about this interesting region of the western Weddell Sea that PICCOLO is so interested in.