Isle of May 2016 – A lover or a fighter? Male mating tactics and the end of the field season is nigh…

Grey seals fighting
Male grey seals fighting for access to females on the Isle of May

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.

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A male grey seal (right) with two females with pups on the Isle of May. Male grey seals are not significantly larger than the females like in some other pinniped species.

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.

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Some pinniped species are highly sexually dimorphic in terms of body size, this is a male New Zeland fur seal which can be three to five times larger than the females.

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.

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Being big and winning fights is not the only way for grey seals males to win access to breeding females, but it’s frequently the most conspicuous!
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Delta playing in a tidal pool, the next time the tide comes in he will go out to sea with the receding tide.

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.

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Eel checking me out. She is massive at over 50kg!
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Oscar in a tidal pool, meeting other weaners and learning how to swim before the tide comes in and he goes to sea.

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.

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Marine litter causes significant health problems, and death, for many kinds of marine life from birds, to turtles to marine mammals. Please pick up your trash and dispose of it properly when you are by the sea!

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!

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The SNH guys leaving the island after their visit, hopefully the trip back was drier than the trip out!

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

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Noisy fulmars on the Isle of May cliffs

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!).

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Fulmar in flight around the cliffs, the strong winds around the island provide excellent opertunities to watch the fulmars soaring around, looking for roosting sites.

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