Following our trip to Isle of Skye I had a couple of weeks of office based work, which allowed me to catch up with some of last year’s photoID data but mainly to finish organizing the upcoming photo-identification season at the project study sites in Dunvegan (Isle of Skye), Kintyre (West coast) and Burray and South Ronaldsay in Orkney. Once protocols, equipment and logistics had been organized it was almost time to head up to Orkney for our second trip in this study area to capture and release harbour seals in order to collect individual data, as we did last year. Like the 2016 trip and the recent Isle of Skye trip, the objective was to capture a number of harbour seals and collect individual data regarding their body condition and health, as well as to deploy telemetry tags on a sample of the adults. This information, collected annually and in different areas of contrasting harbour seal population trajectories, will help us get a better picture of what may be behind the decline in harbour seal numbers in the north and east coast of Scotland and in the Northern Isles, compared to the stable and in some areas increasing numbers of harbour seals in the west coast and Outer Hebrides.
In mid-April we headed up to Orkney, aiming to finish the work within a couple of weeks. Despite having a rather summer-like weather at the start, things turned around very quickly and we were suddenly in proper autumn and winter weather for a good week and a half. We had snow, hail, and wind. And more wind, lots of it, which made working outdoors and in the water rather challenging. The team found extra energy where we thought we did not have it and we were out at every opportunity we had, working double tides if needed.
We were not the only ones disliking the weather though. Not surprisingly, the seals did not enjoy the heavy winds and chose not to use most of the haulouts where they normally would regularly come ashore to rest and decided instead to stay in the water, use haulouts out of our reach or only use those more sheltered. In addition to our limited ability to work given the bad weather conditions, most of the seals we captured in the first couple of weeks were mostly males, similar to what happened during our trip to Isle of Skye. This could have been caused by a segregation in the use of haulouts between the two sexes or maybe just by being unlucky and getting more males caught then females. Despite the challenging conditions our female scoreboard slowly started to fill up. A couple of calm and sunny days allowed us to travel further away to check on other haulouts around Scapa Flow, and we successfully caught another few harbour seals.
Overall, we captured and released around 20 harbour seals of different sexes and age classes and deployed telemetry tags on eight of the adult females. The tags, which are small and lightweight, are glued to the back of the head of the seals and will provide with detailed information on their location, movements and diving behaviour until they fall out sometime close to the start of the annual moult in late July and August.
Despite tagging a very small proportion of the total population, the data we obtain from the telemetry tags are useful and interesting in many ways. For example, the location of the seals will inform and guide the photo-identification effort during the pupping season. Also, by looking at where and how often tagged seals use certain haulouts where the photo-identification data are collected, we can understand how representative our selected study sites (and the results coming out of those) are of the total population of harbour seals in Orkney. The telemetry data can also inform us about potential foraging areas, where we can get fish samples from to look at the prey availability and quality.
The telemetry tags have been reporting back frequently and, similar to last year’s deployments, showing a variety of movements among the seals. The figure below shows the tracks of all 8 adult female harbour seals. For now most of the females have stayed within Scapa Flow or just south of it off Hoy and South Ronaldsay, but one female has taken a trip north to Shapinsay and from there she has been doing longer trips off the NW coast of Orkney mainland. For me I will keep a close eye on the whereabouts of these females, especially as we are approaching the peak in the pupping season in about three weeks’ time. Hopefully I will get to see some of them with their pups while I take pictures, and we can compare my observations with the results from the pregnancy tests conducted during the captures as part of the data collection on individual health status.
I almost forgot! We had an unexpected visit while we were up in Orkney, with a group of three fin whales showing up in Scapa Flow. The good weather conditions and the unusual sight filled up the roads between Burray and Kirkwall with curious observers. What a treat!
Blog post written by Mònica