Monthly Archives: July 2019

Goodbyes to Orkney

Last monday I said my goodbyes to Orkney, as I took the Pentalina ferry from St Margaret’s Hope to Gills Bay one last time. After 4 summers spent in Orkney collecting photo-ID data on the harbour seals in Widewall Bay and Burray, it was time for me to pack my bags and head down to St Andrews. This last season is not quite finished, but I have left in the capable hands of my colleague Emily, who will take over for what’s left of this month of July. By the end of it, most of the pups will be weaned and juveniles and adults will be ready to start or will already be well into their annual moult.

Beautiful morning for a sail to mainland…

The ferry happens to go past one of the monitored haulout sites… last opportunity to say goodbye to the seals!

The last day I went out to get data on my own was on a friday, and what a beautiful day that was! The sun was shining and it felt like proper summer! Luckily it was early enough in the day that it was still cool and not too hazy, otherwise it is really tricky to get photographs of the seals that are actually in focus! Another challenge of these hot and calm days, especially when the tides are not very big, is that the seals will generally not move AT ALL. And when I mean not at all, I mean a seal will be in the same position, belly up and not lifting her head up even once. They can be in the same position for the 3 hours one is observing and trying to get pictures. It is not very convenient for us but highly convenient for the seals, that’s for sure!

Cracking day in Widewall Bay

Or075 and her pup having a snooze. Check how calm the water is below them!

Really quiet days come with little disturbance from weather elements, which means any other sound will be heard by the seals and it has the potential to wake them up. On that day, there were some Eider ducklings at the haulout site in Widewall Bay, and any time they made some noise they managed to wake up a couple of sleeping seals, which got a proper startle!

Eider duck with her ducklings

 

That last day I managed to visit all three main sites, photographing a large proportion of the seals resting (yes, some of them were asleep and impossible to photograph). By this time in the season, the juveniles are looking very ready to moult, looking uniformly brown and feeling itchy… If it gets too hot but you don’t want to get into the water completely, you might as well just dip your head in…

Juvenile harbour seal cooling off by dipping its head in the water…

The pups that were born first are now about 4 weeks old, and probably close to being weaned. They have gone from being a bag of skin and bones with little blubber to big round balls of fat. The lactation period might seem short (about 24 days; Bowen et al. 1992, 2001) compared to other mammals, but it is highly efficient and intense, as harbour seals secrete large volumes of energy-dense milk with 40-60% fat. Female harbour seals do not have enough body energy stores to fast throughout the  lactation period. To make up for the energetic cost of lactation, females will forage during that time, starting with short foraging trips lasting only a few hours about a week after giving birth.

Or062 and her pup, also a female, looking very big by now…

Through this project we have been able to gather information on individual seals over 4 separate summers. This longitudinal individual data is key to figure out population dynamics questions, which is the same as saying we are trying to answer questions about what is causing the numbers of harbour seals to go up or down in different areas. Are there not enough pups being born? Are these pups surviving as one would expect for a seal? What about the juveniles or the adults? Or are there any differences between males and females? We might not have enough data to answer all these questions given the length of the study (4 summers is not much compared to how long seals live), and the limitations of following pups onto adulthood, but we are hoping to be able to answer some of them.

There are other interesting facts associated with the data we collect. We can see, for example, differences in how females succeed at pupping every summer. Some will pup earlier than others in the season, some will not pup in a given year, some will not manage to wean a healthy pup while others end up weaning pups that are bigger then the one-year-olds.

Or094 with a pup in 2016, 2017 and 2018, but on her own in 2019

As an example, below are two photographs of Or118 and her pup from this year. The time difference between the photographs is 3 weeks. And check how much bigger the pup is by then!

Or118 and pup on 21st June, about 2 days after being born

Or118 and pup on 13th July. Look at the difference in size in those 3 weeks!!!

Four summers of observing the same seals has other rewards, as one gets “to know” the different individuals. By this I mean not only learning to recognize them in the field but also noticing that different seals do different things, and these differences in behaviour sometimes repeat across years. Some seals seem to have favorite spots to haulout, as they will repeatedly be found in that elevated rock, day after day and year after year, like Or057 in the picture below. Different seals are more or less tolerant to having other seals nearby, and females might be more or less patient with approaching pups.

Or057 in one of her favourite rocks, year after year…

In a way that does help to collect data every summer because one can kind of predict what certain seals might do next. There are some behaviours that generally apply to all seals too. For example, seals do not like heavy rain (who would have thought?), and will slowly (or not so slowly) leave the haulout site and return to the water if there is too much rain. Also, seals will tend to follow a pattern of movements within the haulout site at different times of the tide, and depending on how close to neap or ebb tides it is in the cycle. When females come out of the water with a pup, there is a short window of opportunity to get the photographs done, as the female will position herself quickly for the pup to suckle but then will lay with her head down and thus will make it impossible to get a picture.

I am taking with me all of this knowledge and fieldwork memories, which I am sure will remain with me for a long time. Now, however, it is time for some office work to deal with photograph processing and analysis. Let the fun bit begin!

Written by Monica

References

Bowen, W.D., Oftedal, O.T., and Boness, D.J. 1992. Mass and en-ergy transfer during lactation in a small phocid, the harbor seal(Phoca vitulina). Physiol. Zool.65: 844–866

Bowen, W.D., Iverson, S.J., Boness, D.J., and Oftedal, O.T. 2001.Foraging effort, food intake and lactation performance depend onmaternal mass in a small phocid seal. Funct. Ecol.15: 325–334

Pupping season rapidly progressing in Orkney

Out of the three study sites (Kintyre, Isle of Skye and Orkney), Orkney is the one in which the pups arrive the earliest, normally by mid June. Consequently, it also tends to be the site in which most, if not all pups, will have been born sometime by the start of July. Because this is our 4th season in Orkney and I have been working on matching seals from this area for a few years, I do by now have a very good knowledge of the seals that are found at the monitored sites here. It also helps that the haulout sites themselves are not massive in numbers, making the catalogue of seals under 200 animals for this area. This is not the case in our study site in Isle of Skye, Loch Dunvegan, for which the catalogue currently holds over 500 seals.

Size of catalogues of identified seals in Kintyre, Orkney and Isle of Skye. The orange bars indicate the number of catalogued seals for each side (Front, Left and Right sides of the head), and the blue bars are those that might be new to the catalogue and are yet to be assigned a number if agreed these are indeed new individuals.

The advantage of recognizing the seals is that we can identify them on the spot as we collect the data in the field, which is very safisfying. Every photograph that gets taken in the field is subsequently entered in an excel data table, so that we can store the metadata associated with each photograph. Each photograph will be graded for its quality, and we will make a note if what we can see is the right, the left or the front side of the seal’s head. That is because the pattern will be different on each side, so technically we end up with three different catalogues.

We always try to get the left, front and right sides of each seal, as shown with Or118 here. It’s not always the case though!

We will also note whether the seal is associated with a pup or not, and whether we can see the pup in the photograph or if it is suckling. Other relevant information that will be noted is if we can see a seal is pregnant, if we can sex the individual or if there are any significant or unusual injuries.

Keeping track of who is at the haulout sites on a daily basis means we can monitor in situ not only who is present that season, but also which females are likely to be pregnant and which ones are having pups and when. The first pup arrived on June 12th in Widewall Bay (South Ronaldsay), belonging to female Or075. The last one was on July 1st, from Or026 (aka Pirate), who, coincidentally, was also the last female to pup last year.

Or075 with her pup on June 12th. This female was still pregnant on June 10th.

Or075 with her much bigger pup on July 7th

Or026 (aka Pirate) looking very pregnant on June 30th

Or026 with her pup on July 7th. Note that the pup has a very distinct white mark behind the left ear, which should make it easy to identify it through the season.

The pups are rapidly gaining weight with the fat-rich milk from their mothers. In just a couple of weeks from now most of the pups will be weaned, especially those born earlier in the season.

Milk moustache from Or062’s pup

Look at the size of these pups! Nothing like what they looked like when born.

As days go, the females will undertake foraging trips during lactation, to support its energetic costs. The pups will accompany them in many of those occasions, but they will also stay behind and wait for their return on shore. Some pups can be seen resting, while others will spend time in the water, or will be checking on other females and other pups, sometimes calling out. When the females return, they will look for their pups, checking on any sleeping pup around until they find theirs.

On July 8th, I spotted female Or007 approaching a haulout site from the water. She can be easily recognized from the distance because she has some scarring around the neck from some debris that got entangled around her neck sometime in the past. There is no debris left now, just a scar. This haulout site is pretty small, normally holding around 10 to 20 seals maximum. On arrival, Or007 first headed towards a mum pup pair, Or044 (aka “Butterfly”) and her pup, and checked on the pup.

Or007 checking on Or044’s pup… not her pup…

Not recognizing it as her pup, she then went on to check on another mum pup pair, this time Or135 and her pup. Wrong pup again… although the pup was quite interested and had intentions to follow this different seal into the water!

Then checking on Or135’s pup… wrong again!

Then she went onto checking a sleeping pup nearby and … hurray! Third time lucky as she finally found her pup, who was just snoozing, completely unaware of what was going on. After some nose-to-nose interaction, mum positioned herself so that the pup could suckle.

Or007 finally re-uniting with her pup!

Or007 with her pup suckling

And here is a short video of Or007 looking for her pup on that day:

The following day, July 8th, Or007 must have gone again on a foraging trip, as I spotted her pup on a nearby haulout site having a rest after checking the seals that were around.

Or007’s pup settling for a rest at the haulout site

For the next three weeks we will keep on monitoring the mum pup pairs at the haulout sites. A part from those, there are also juveniles, adult males and adult females that have not had a pup this year. The data we collect on them (i.e. whether they are present or not) will help us learn more about the mortality rates in different study sites, to see what might be behind the contrasting trajectories in harbour seal numbers in different areas of Scotland.

Written by Monica