It has been a long time but we are back to update on the Harbour Seal Decline Project! We spent most of the autumn and winter processing all the data that were collected during 2016 (keep tuned for updates on that!). After months of office based work we were out again on our first fieldwork trip of 2017. In this first trip we headed up to Isle of Skye in early March, with the objective of capturing and releasing harbour seals to obtain individual data on their health and condition as well as deploying telemetry tags. The sites chosen to capture seals are located in Loch Dunvegan, and include the skerries where later on in the summer Andy will be collecting photo-identification data of the seals in collaboration with the Dunvegan Castle seal boat trips. These haulouts in Isle of Skye represent our study area where numbers of harbour seals have been stable or increasing, compared to haulouts located in our other study area in Orkney, where numbers have been declining by 75% since around the year 2000.
After a long day on the road we arrived to Dunvegan Castle where we met with some of the staff who very kindly showed us how to access the boat slip. The sight of around 100 seals hauled out right opposite to the boat slip was a nice welcome. However, the weather did not want to play the game and we had a good share of rain, wind and hail, with temperatures below 5 degrees for a good week. Given these conditions we started by checking out the more sheltered skerries close to Dunvegan Castle. During the first catching attempts we kept on capturing adult males, but not a single female, suggesting different haulouts might be used differently depending on age and sex.
To try and have a better idea of haulout composition, we took a road trip with the scope and the camera . The photographs confirmed that the haulouts we were targeting were dominated by males. We then learned that the boatmen in Dunvegan had named one of the skerries as ‘male island’… no surprise there! This segregation between haulout sites is known to occur in harbour seals, as other studies have shown (see for example the study by Thompson 1998 on harbour seals in Loch Fleet, Moray Firth, or the one by Harkonen and Harding 2001 in Norway.)
In the current study we are mostly interested in adult female harbour seals, as information on their survival and birth rates will be compared between sites of contrasting population trajectories. With the hope of encountering a higher proportion of females we waited for a window of good weather and traveled to haulouts closer to Skinidin and Colbost. Luckily for us those haulouts had a better male to female ratio.
After the slow start we finally started to get more females, and deployed 8 GSM-GPS telemetry tags on adult females. These are the same type of tags that were deployed last year in Orkney, and will inform us about the movements and diving behaviour of the seals, as well as their whereabouts during the pupping season. The combination of snowy days and a last day of pure sunshine and calm seas left us with incredible views of The Cuillins. Since the tags were deployed we have been receiving regular updates on the seals’ location and movements. Below are maps with the movements of some of the tagged seals, showing individual differences in the extent of the movements as well as the areas visited by each of them.
The tags, which are glued to the back of the seal behind the head will stay on until they fall during the moult sometime in late July or August. During the pupping season they will inform us on the seals’ whereabouts, and hopefully the seals decide to stay around Loch Dunvegan for Andy to check on them and (hopefully) on their pups. Keep tuned for updates on these Skye seals and on our other trip to Orkney!