Ringed seals in the Arctic Ocean
Nine ringed seals are now swimming around with brand new, advanced satellite transmitters. One is already at 84° N, far North of the ice edge of the Arctic Ocean. Our field work is concluded, and the Norwegian Polar Institute is now monitoring the incoming ocean temperature, salinity and flourimetry (algae production) data from the areas whereever the seals travel.
Ringed seals and ICE – third and last field report for 2010
We are now cruising out of Wahlenbergfjord on the west side of Nordaustland after setting out the last of the satellite tags last night. We had a lot of challenges trying to capture ringed seals up in Duvefjorden because the water was crystal clear and the seals saw the nets despite the fact that they are made of “invisible” monofilament.
The three seals we got up on the north side were captured by locking each seal into a lagoon with nets closing the mouth and then one of us driving a zodiac inside the lagoon to encourage the seals to go out (i.e. into the net). This technique worked well, but few seals visited the lagoon and the current was so strong when the tide was running hard that the seals just swam right through the tight nets which meant many hours every day or two mending the nets and many frustrating times when seals were so close at hand but not captured.
Many years ago we had been down in Wahlenbergfjord capturing narwhal and seen reasonable numbers of ringed seals so we headed that direction to try our luck. Wahlenbergfjord has many glacier fronts and glacial output rivers, so the water is cloudy. Of course, fishing in ice-filled water has its challenges too.
But, things went very well despite being plagued by drifting ice and in the last three days we put out the remaining 6 satellite tags.
At the outset we had 10 CTD-fluoro-SRDLs built for the project, but one of them did not survive the rigorous pre-deployment testing procedures, so our sample size was reduced to nine. These are not tags that you can just pick up at a shop. They are the most complex biotelemetry developed to date for studying marine mammals.
Sea Mammal Research Unit (SMRU) has as a basic unit (satellite-relay data logger – SRDL), a tag that provides detailed information on diving behaviour, which is vastly more advanced than commercially available tags from telemetry companies. But, additionally, SMRU produces a CTD-tag that measures conductivity and temperature using sensors produced by a commercial oceanographic instrument producer (Valeport, from Devon, UK).
SMRU integrates these sensors into their dive-loggers when building CTD-SRDL tags. After integration of the sensors at SMRU, the tags go back to Valeport for testing in pressure tanks that put the tags under pressure similar to what they would experience at 2000 m depth, under various conditions of known salinity and temperature (a predeployment calibration).
The newest development – the Fluoro-CTD-SRDL – incorporates yet another instrument, a fluorometer produced by Turner Instruments, called a Cyclops 7 into the CTD-SRDL. After this piece is added to the tag at SMRU, the unit is field tested at sea beside oceanographic CTD instruments and stand-alone fluorometers.
In our case, all of our tags were sent to France, where our French colleagues took them out to sea in the Mediterranean. One of our units did not perform well enough and so went back to the lab to see if parts could be salvaged.
Ringed seals are most easily captured in the spring when they lay up on the land-fast sea ice, resting around breathing holes. They give birth to their young and breed in fjords containing stable land-fast sea ice all around Svalbard. When these activities are done for the year they also undergo moulting on the ice.
All seals lose their worn hair once a year, replacing their old coat with a shiny new one. The Arctic seals prefer to do this while resting on sea ice where they can circulate blood to the skin to make moulting happen as quickly as possible with minimal heat loss. When they moult in water it costs them a lot more energy (and is presumably less comfortable). After their moult the seals leave the areas where the fast-ice is virtually gone for the year with the approach of summer.
Satellite tags are expensive equipment and we want them to stay on the animals and report data for as long as possible, so we prefer to glue them onto new hair, shortly after moulting so that they last as long as possible. This is why we are out catching ringed seals in summer even if it is much more difficult than it would be during spring.
Once ringed seals are captured they are generally very easy to manage. Few bite and they are not so big, so we do not drug them. They are usually quite calm under the whole capturing procedure once they are out of the drift nets and comfortable in a holding bag in the boat at least.
We glue the satellite tags onto the fur using two-component epoxy. But, first we weight the seal, determine what sex it is, and take a blood sample and a blubber biopsy for diet studies (stable isotopes of nitrogen and carbon analyses of the blood and fatty-acid analyses of the blubber).
The whole handling procedure takes about 15–20 minutes. Then the seal is released after an obligatory photo-session, during which this camera-shy species rarely co-operates.
On the results front – we can report that our seals captured up in Duvefjord are already up at the northern ice edge up at 82° N. But, remarkably, before heading north one of them did a round-tour of Nordaustlandet first (!? – see the map).
So while we tuff out of Wahlenbergfjord with a course set for Longyearbyen, we are happy and satisfied.
We look forward to coming home and following the seals over the fall and winter, studying their behaviour and seeing what they can ”tell” us about the environment they encounter up here at the top of the world.
Kit and Christian