The time has come for the PHATS team to pack up and go home as almost all the grey seals have left the Isle of May and returned to sea. We have all got back to mainland safe and sound, and everyone is looking forward to some well earned rest after almost two months of fieldwork. All of our laboratory equipment and samples were packed up and shipped off the island without incident, and everything is now at our labs at Abertay University and the Sea Mammal Research Unit, ready for analysis in the new year.
There were only nine of our study weaners still on the island during our last survey, and the majority of them are on the edges of the colony ready to go to sea. Oscar is still hanging out in his pool off the south end of the island, and Papa and X-ray have both made it to the bottom of the southern cliffs and are playing and dozing with a bunch of other weaners there. Hopefully they will all find their way out to sea and learn to forage and catch fish in the coming months. Even if they do survive their risky first year, it’s sadly unlikely that we’ll see them anytime soon on the island again. Grey seals usually don’t come back to breed for at least five years if they are female and even longer if they are male. If they do return to the colony however, we’ll be able to identify them from the number on their orange flipper tags, and if you see any seals with tags please do let us know so we can work out which of our study animals you saw.
These kind of mark-recapture methods are used in all sorts of studies on many different animal species, which I was reminded of during the last weaner survey before we left. While searching the southern cliffs I came across a shag with a ring on its leg, which marks it as one of the study individuals the Centre for Ecology and Hydrology has captured, ringed and released back into the wild to help collect data on seabird population dynamics and behaviour. If you see a ringed shag (the leg rings can be several different colours, not just yellow with black writing like the one I saw below) please email the sighting information to firstname.lastname@example.org and if you are interested in the project’s work then you can keep track of what is happening through their twitter feed @CEHseabirds. This particular bird was ringed as a chick in 2000 on the Isle of May, which makes her 16 years old and she has raised 26 chicks so far in her life (information courtesy of the Centre for Ecology and Hydrology).
The PHATS team will be back out in the field in January 2017, when we will return to the Isle of May to look for moulting grey seals. The majority of individuals will enter the moult later in the year at around March/April time, but there are always some seals that start early. We will resume blog updates then, so in the meantime we all wish you Merry Christmas, a Happy New Year and hopefully see you in 2017!
Thus far in this blog I’ve mostly focused on talking about the grey seal mothers and pups which live on the breeding colony here on the Isle of May. The PHATS project only involves collecting data from mothers and pups at various ages, hence I’ve somewhat ignored the other occupants of the colony up to now. However, the other individuals on the colony show plenty of interesting behvaiours too, so this particular blog is going to be about the male grey seals that live on the Isle of May at this time of year, waiting to try to compete for opertunities to mate with the females.
Male mating tactics in species of pinnipeds (seals and sea lions) tend to depend on how sexually dimorphic (differences in size or external features like horns between males and females) the species is and the type of habitat they breed in. Some pinniped species, such as elephant seals, have males that are much larger than the females of their species. This facilitates establishing a territory on a breeding colony that contains as many females within it as possible, defending it from rival males and keeping lots of females inside. These huge males will fight any other males that intrude in the territory to prevent them from entering and mating with the females within. Other pinniped species that breed on ice in the north and south poles of the world use physical features like breathing holes to define where males establish territories, like Weddell seals in Antarctica. Male Weddell seals are a similar size to their female counterparts and use complex vocal displays underwater to defend their territories around breathing holes rather than physically fighting with other males.
Grey seal males show a variety of mating strategies on and around breeding colonies. Males in this species are not much bigger than the females, so creating and guarding large groups of females to mate with (a harem) is not possible. Some males do establish loosely defined territories across various areas of the breeding colonies, but these do not seem to be anchored to physcial features or resources in the colony. The males that compete to stay within the colony amongst the females are called as tenured males and they typically the largest males on the colony, fasting to hold their position in the colony for as long as they physically can before they must return to sea to feed. However, there are alternative mating strategies that males can use to gain opportunities to access receptive females, including intercepting females that are returning to sea when leaving the breeding colony and mating with females at sea. Some male grey seals do return to sea and engage in shallow and deep diving behaviour during the breeding season, but whether these can be attributed to feeding, displaying to attract mates or aquatic mating with females is not currently know. Therefore there seems to be a variety of mating strategies that individual male grey seals can employ on breeding colonies to gain access to females, and future research will hopefully help us understand which are the most successful and how selection pressures have encouraged the development of the different mating tactics.
The PHATS research project is almost complete as the end of the field season is quickly approaching. We only have two samples left to collect, then we will pack up and head off the island just in time for Christmas! Over half our study weaners have now gone to sea, there are only 13 left on the island. The oldest remaining seal is India at 49 days old, but we still have some fairly young weaners like Eel (not in the phonetic alphabet I know but we always run out of alphabet and have to start giving study weaners name codes like AA, BB, CC… and Eel is EE!) who is only 26 days old and still over 50kg. She could hang around the island for quite a long time with all that blubber mass, we have known weaners to remain on the colony for over a month after weaning.
Sadly, while doing the daily colony survey to find our study weaners I also found a weaner that had plastic wrapped around his neck. I managed to deprive him of his ‘necklace’ and he swam off into a pool without serious harm, but it’s a sad reminder of how abundant marine litter is, and how it can cause deadly problems for marine life around our shores. Please be aware of your litter, whether you are on the coast or anywhere outdoors as many speices of creatures can end up trapped or eating the things we throw away, causing severe health problems that they frequently cannot alleviate by themselves.
MEANWHILE Away from the colony,we had some visitors for the day this week as some people from Scottish Natural Heritage came out to the island to prepare for the field station closing down for the winter. There are people living on the island almost every month of the year as bird researchers come out in the spring and stay studying the birds until early october, then the seal researchers move in until mid December. However, between December and spring there are a few weeks when no one is living and working at the field station so everything had to be cleaned, packed away and locked up against the winter storms. It was nice to see some new faces after 2 months of seclusion and everyone had a great day despite the choppy sea conditions getting to and from the island!
The island has also become noticeably more noisy in the last week as the cliffs have become covered in sea birds returning from offshore early to roost. We currently have lots of guillemots
and fulmars on the cliffs and it is lovely to see some more life on the island, especially now there are so few seals around. With the seals departing, and our project coming to an end this year, we will likely be leaving the island in the next week to head home. Going back to mainland after a few months away from society is always a little strange, but everyone is looking forward to seeing their loved ones (and getting regular showers again!).
Even though it’s december and the vast majority of the seals on the Isle of May breeding colony have already raised their pups and returned to the sea, we are still seeing a few newborn pups from mothers that are late season breeders. Most of the colony is quiet now as the majority of adult females have gone, leaving their weaned pups (weaners) in their 2-3 week post-weaning fast (see this blog for more details about the post-weaning fast in seal pups).
Back at the PHATS lab, things are starting to wind down. We had to ship all the samples we had generated so far from the cell culture experiments off the island this week as we had filled the minus 80 freezer on the island! The tissue, media and blood samples we’ve collected over the last 6 weeks will give us plenty to study back on the mainland in the new year. Our daily surveys of the study weaners have shown that two of our weaners, Charlie and Alpha, have left the island and gone to sea! Charlie was 35 days old when she left the colony, and Alpha was 43 days old. Some of our study weaners don’t seem very keen to go, both Bravo and Delta are 43 days old and still happily playing around on the island! Some of our seals are making their way through the colony and the rocky tidal region of the shore towards sea, like Foxtrot who is 40 days old and is on the southern edge of the island.
MEANWHILE the research team on the island has dropped to just 4 people as half the team left the island this week to return home, the remaining two researchers from the Durham University seal behaviour team and two research assistants from the Sea Mammal Research Unit of St Andrews. We also were lucky enought to be visited by one of the bird researchers from the Center for Ecology and Hydrology again, as they keep track of the ringed sea birds (shags) on the island during the winter. During this visit they caught and ringed a wild short-eared owl and were kind enought to show us before they released her, beautiful!
It’s currently my favourite time of year on grey seal breeding colonies, when the weaned pups (weaners) start to out number the adults on the island. I do enjoy watching the huge variety of behaviour the adults display, from the caring maternal behaviour mothers exhibit to the impressive battles males fight for access to females, but the weaners are without a doubt my favourite. This is because they typically spend several weeks on the island after weaning in a post-weaning fast, where they stay on the breeding colony despite there being no food for them, and they usually spend this time playing and exploring their surroundings. They can be very curious, and some will even come right up to you when you’re hiding in the colony to see what you are, play with youre belongings or even fall asleep on you!
Post weaning fasts are common in Phocid (true seal) seal species around the world, from the huge elephant seals to the two species we get in the UK, grey and harbour seals. No one really knows conclusively why weaners stay on the breeding colony for several weeks after their mothers wean them, although there are lots of theories. Grey seal pups can lose half a kilogram of mass every day they remain on the colony after weaning, and as having large amounts of blubber increases the chances that the pup will survive it’s first year of life, it seems very strange that pups stay on the island rather than go to sea to learn to forage and catch fish. However, there is evidence that during the post weaning fast, pups undergo physiological changes which prepare them for going to sea for the first time, so they can hold their breath and perform deep dives so they can catch fish successfully. In grey seal pups, the amount of oxygen they can store in their blood increases during the post weaning fast due to changes in the volume of blood they have and its components, with increases in substances such as hemoglobin that bind oxygen. The more oxygen a pup can store in it’s blood before it dives, the longer it can hold it’s breath and forage underwater, and in theory the more successful at catching fish it will be.
There are still many unanswered questions about the post weaning fast phocid seal pups go through and what happens once weaners leave the colony for the first time. To try and answer some of these questions, one of the senior scientists (Dr Sean Twiss of Durham University) here on the Isle of May is currently looking for a PhD student to investigate “Patterns of individual variation in post-weaning behvaiour in wild grey seals“, and the project is being co-supervised by my boss, PHATS team leader Dr Kimberley Bennett of Abertay University! The deadline for applicants is the 20th January 2017, and if you are interested, the details of the project and how to apply are found here. Whoever gets the PhD will get to come out to the Isle of May next year and will meet me and the rest of the PHATS team! Matt Carter of Plymouth University, another PhD student that Dr Bennett co-supervises, is also currently investigating the development of foraging behaviour in pups leaving breeding colonies, so hopefully in the coming years we will gain a much better understanding of the factors driving weaner behaviour before and after they go to sea for the first time.
In the lab here on the island the PHATS project is just over halfway to completion this year. As it gets later in the breeding season we are getting more and more study weaners to keep an eye on, although some of the first weaners that we included in our study are approaching the time when they may go to sea for the first time, at about a month of age. Charlie is now 35 days old and much leaner than when she first weaned from her mother 17 days ago, having lost 9.6kg across those 17 days. This seems like a lot, but considering she put on 22.2kg of blubber in the 18 days she was with her mother, she is still large enough to successfully go to sea. Kilo has now fully moulted and has a very distinct pattern of spots that we can identify him from. We also have a new study weaner (Oscar) that has moulted and turned out to be completely black!
MEANWHILE away from the colony, it briefly got a little bit harder to escape from the seals as a female came right up outside our doorstep with her pup for the first time! She has thankfully moved on a little further from the house so we don’t disturb her, but it was a suprise to open the door one morning and find the pair of them staring at us!
Sadly two members of the research team here have had to leave the island in the last week, Dr Twiss and Dr Bennett both had to return to the mainland to resume their teaching duties at their universities. They will be missed, and it marks the beginning of the end of the field season as the majority of the researchers here will also leave in the coming week. The PHATS team will stick it out until mid December, but it’s always sad to see people go!
Finally if you’d like to see Dr Bennett talking about seals or the PHATS project, she will be giving some public presentations in the coming weeks in Scotland:
6pm, Tuesday the 13th December at the D’Arcy Thompson Zoology museum at Dundee University: Public talk on seal biology