In the news! New paper on the development of at-sea behaviour in male southern elephant seals at Marion Island

The at-sea behaviour of southern elephant seals is largely influenced by their ontogeny, which refers to the development of a seal from one life stage to the next. As seals age and grow, they experience changes in their morphology and physiology, which influences their diving abilities and movement patterns.

In our latest article published in the Journal of Experimental Marine Biology and Ecology, we aimed to observe the at-sea diving behaviour of male southern elephant seals from Marion Island - an aspect not previously studied.  

An adult male southern elephant seal at marion island, fitted with a satellite-linked time-depth-recording tracking device. photo: nico de bruyn

Between 2005 and 2011, satellite trackers were deployed on 23 different male southern elephant seals of various ages. Trackers recorded seals’ locations, dive durations, dive depths, surface durations and dive frequency. This allowed us to distinguish two behavioural modes; namely when seals were moving within a small area, and potentially foraging, and when seals were transiting between areas. We constructed models with this data which determined the influence of age class and behavioural mode on the diving behaviour of male southern elephant seals.

We found that juvenile seals travelled the furthest distances from Marion Island and were in transit mode for most of their dives. This behaviour was attributed to the younger seals’ less developed ability to locate food, and their smaller body size, leading to lower energy requirements. Juvenile seals also displayed shorter dives and reached shallower depths which was expected given their physiological limitations. Moreover, younger fatter seals are more buoyant and have limited oxygen reserves which limits how deep they can sink.

Fig. 1 from Lasch et al. 2022. (A) State-space modelled locations for 23 male southern elephant seals tracked from Marion Island between 2005 and 2011. (B) The average maximum distance travelled (km) by juvenile (n = 5), sub-adult (n = 8) and adult (n = 10) male elephant seals from Marion Island.

In contrast, sub-adult and adult seals stayed relatively closer to the island and spent most of their dives in searching mode. These older age classes also displayed longer and deeper dives and spent more time at the surface than younger seals. Sub-adult seals experience a secondary growth spurt, growing up to 10 times in size. This drastic growth increases their energy requirements and enhances their physiological capabilities, which enables them to exploit food patches for longer periods of time. Moreover, their longer surface durations are explained by their need to recover their oxygen supplies after long and deep dives.

Observed differences in the at-sea diving behaviour seem to reflect changing physiological abilities as seals mature. For male southern elephant seals, changes in physiological ability necessitate behavioural plasticity, which may be the key to survival and future breeding success.

To find out more, check out the full article HERE

Lasch KG, Tosh CA, Bester MN & de Bruyn PJN. 2022. The ontogeny of at-sea behaviour in male southern elephant seals (Mirounga leonina) at Marion Island. Journal of Experimental Marine Biology and Ecology (in press). https://doi.org/10.1016/j.jembe.2022.151833.

News just in! An amazing geospatial database for the sub-Antarctic Prince Edward Islands is now freely available.

Figure 2 from Rudolph et al 2022: The datasets created from the (A) digital surface model (DSM), using Marion Island’s datasets as an example. (B) A slope raster and contour lines, (C) an aspect raster and (D) hydrological features such as drainage lines and lakes. The hillshade raster has (E) minor artefacts caused by interference in reflectance data by either cloud cover, scoria or snow. (F) Regions on Marion Island where artefacts in the DSM will affect the accuracy of derived geospatial data.

In exciting news, researchers working on data from sub-Antarctic Marion Island and Prince Edward Island have produced and published a detailed topographical and hydrological geospatial database – produced from a 1 m x 1 m digital surface model of the Prince Edward Islands.

The Prince Edward Islands are considered sentinels for terrestrial and marine research in the southern Indian Ocean. Their location, just north of the present-day Antarctic Polar Front, combined with the hyper-maritime climate, creates the perfect opportunity to study the ecosystem responses to climate change.

Prior to this publication fine-scale, high resolution geospatial data for both multi-and transdisciplinary research was missing. This resource will be a crucial component in allowing researchers to better analyse fine-scale biotic–abiotic interactions of the Islands’ landscape and

ecosystems especially within the context of climate change and the impacts of invasive species.

Lead author Liezel Rudolph expressed the value of such a research resource saying, “… it will facilitate collaborations between scientists in the abiotic and biotic fields, and, as it’s freely available, it invites young scientists, school teachers and the general public to use the data for their own education or interests!”

Not only will this resource benefit scientific endeavours it will additionally aid in education and conservation efforts particularly looking forward to the planned mouse eradication programme on Marion Island which will require detailed and precise geospatial data to support the planning of the world’s largest mouse eradication programme from an island (if successful).

FIGURE 4 from Rudolph et al 2022: A preview of the map indicating names and codes of beaches and zones used in marine mammal monitoring research programmes (MIMMP research) at Marion Island.

The database contains vector files, raster data sets, and maps of topographical and hydrological parameters, which are freely available to download from Figshare, which is an open access data repository. Included within this are maps indicating names and codes of beaches and zones used in the MIMMP’s mammal monitoring research programmes on Marion Island with detailed descriptions and coordinates to provide for cross-referencing with our very own database (figure above).

With such a vast data resource now freely available, the authors encourage the South African polar science community to share data on similar platforms to improve the research resources available.

The full suite of data can be downloaded HERE.

Citation

Rudolph EM, Hedding DW, De Bruyn PJN, Nel W. An open access geospatial database for the sub-Antarctic Prince Edward Islands. S AfrJ Sci. 2022;118(9/10), Art. #12302. https://doi.org/10.17159/sajs.2022/12302

Sealer Diaries: A day in the life of a Marion Sealer

Written by Mike Ross (M79)

Before I came to Marion Island, I asked several old Sealers what a typical day on Marion looked like. Most replied that there was no such thing as a “typical day” on Marion, an answer which, although undoubtedly truthful, was not especially helpful. Since I have now spent some time on Marion and have been inducted into the hallowed community of Sealers, I will do my best to provide an answer to the “typical day on Marion” question which is both truthful and informative. If nothing else, I will at least describe a single day in the life of a Sealer on Marion Island. Bear in mind that we Sealers have only just arrived on Marion (well 3 months ago, but it feels much shorter than that), and that we are yet to experience the mayhem of the breeding season, which will be quite different to a day during the quieter winter months. Having said that, this is a typical day…

First some background. Sealers on Marion work with both southern elephant seals (Mirounga leonina) and two species of fur seals, though mainly elephant seals. Our schedule is generally governed by the 10-day elephant seal census, which covers all the beaches on the eastern side of the island. Every seal born on Marion is tagged, with all individuals born in a year given the same colour tag (a different colour to those born in other years), but a unique tag number. The census typically takes five days (and a sixth if you include the walk back to base from one of the further huts), with three nights away from base at various huts scattered around the island and involves recording all the elephant seals one encounters at beaches around the island, both tagged and untagged. While simple in principle, in practice it is more challenging, as one must get close enough to read the numbers on a tag, while avoiding getting chomped by the rather large, and occasionally quite irritable seals. The remaining four days are spent tagging fur seals, recording previously tagged fur seals, processing scat, entering data or helping with killer whale observations. Back to the crux of this blog!

A young elephant seal bull and female hauled out. These seals are censused every 10 days on the eastern side of the island © Mike Ross

For some reason I woke up at 5:30 am, and given I’m a morning lark, I decided to make the most of my alertness and get stuck into this blog post. After an hour of writing, I packed the last few items into my bag. I was scheduled to finish up censusing elephant seals just north of base, but planned to return to base in the afternoon, so my bag wasn’t too full. I packed my notebook and pencil, waterproof slate (for when it invariably starts raining), binoculars, PG camera (more on this later), tags for foreign seals and tag applicators, waterproof pants and rain jacket, PLB (personal locator beacon in case of emergency), personal camera, a flask full of tea and snacks (you can never have too many, but you can certainly have too few – a most unpleasant experience). I quickly ate breakfast, signed out on the register (so people could locate me if I didn’t come back) and left just before 8 am.

I decided to walk to the furthest point and census the beaches on the way back. The weather teased me – it was sunny over the interior, but I was walking in a soft drizzle, a classic Marion soft, subtle soaker. Nevertheless I enjoyed the 1h30 hour walk to Blue Petrel Bay to the north of base, and marveled at the growing Wandering Albatross chicks and Giant Petrels I spotted along the way. Sometimes I take these sights for granted, but am quickly reminded of how lucky I am when I take a moment to reflect that “I’M ON MARION FREAKING ISLAND” (a direct quotation I discovered on the inside of one of the hut doors which seems particularly apt). At Blue Petrel Bay my work for the day began in earnest.

The beaches are relatively quiet at the moment, with most of the seals fattening themselves up in the ocean before the breeding season. As a result, census went quickly. I came across many tagged seals and recorded their tag colour and number. The highlight was seeing my first Red White (Red White 029), an eight year old male who was tagged in 2014. So far we haven’t seen many fully grown adults, but they are sure to be on their way as breeding season approaches. I proceeded to PG the Red White. Essentially you take multiple photographs of the animal from different angles and combine all these images to produce a 3D depiction of the animal, which can then be used to estimate the animal’s weight. Effectively you can weigh a multiple ton elephant seal with one finger. There are nine beaches between Blue Petrel Bay and base, some with multiple divisions, and I checked them all, encountering 84 seals. Unfortunately I didn’t see any killer whales during my census, but I did briefly stop to admire the view from the top of one of the beaches called Ship’s Cove. Just before I reached base, I stopped to check in with Monica (M79 sealer focused on killer whales), who was at Kill Point, on the lookout for killer whales. By 2:30pm I was back at base.

“I’M ON MARION FREAKING ISLAND” moments as you look down on Ship’s Cove ©Mike Ross.

The day wasn’t done yet. After a quick lunch, M79 sealer Banele and I headed out in an attempt to catch a fur seal mom and her pup. We were hoping to deploy a GLS device (a archival tracking device) on the mom and tag her pup. Alas, the pair conspired against us, and the pup went swimming with his friends, leaving us unable to identify him. Banele and I sat behind a rock for 20 minutes hoping the situation would change, but it appeared to be in vain. I checked in with Monica again (she was at Kill Point for 8 hours, so there was plenty of time for that) and then headed back to base. Once at base, I spent the next hour inputting the data I had collected from my day in the field and clearing the slight data backlog. The work day was now officially over. I’d walked 15.6 km outside (though walking on Marion is much harder than the distances alone suggest) and would go on to do over 28000 steps for the day.

Still, the day wasn’t done yet. On Marion we seem to have never-ending skivvy (cleaning) duties, including the base skivvy, the science corridor skivvy, our accommodation skivvy, kitchen skivvy and braai skivvy, which we do on a rotational basis. Today, being a Monday, was base skivvy, so I spent 30 minutes cleaning various sets of staircases, my job for the day. The last thing I desperately needed was a shower. By the end of the day, one exudes this awful stench of seal and penguin excrement, which as a sealer you become somewhat accustomed to, but the rest of the base personnel do not. Having a shower therefore constitutes an essential part of maintaining relationships with everyone else on the island and avoiding being kicked out of base.

By 7 pm, I had finished everything, just in time for dinner, which after a long day out, is always a highlight. After dinner I organised what I would need for the following day and then caught up on messages and emails. The day ended with some quiet time reading, and then I was off to bed, ready to do it all again tomorrow.

My first Red White tag for the season, an 8 year old bull ©Mike Ross.

Census repeats itself at least every 10 days throughout the year, and while every day is different, I hope you have some idea of what a typical day looks like at this time of year, and if nothing else, at least what happened on this particular day. Marion is the most incredible place, and I feel so lucky to be here. While this post dives into what exactly a Sealer gets up to on Marion, upcoming posts will help explain why the island is so special, and why our work here is so important, so stay tuned! 

Two-year funded Postdoc Position: Space weather influences on marine mammal movement

We are seeking a postdoctoral candidate to investigate whether space weather influences marine mammal movements at sea. Specifically, this study will aim to collate telemetry data from a range of Southern Ocean marine mammal species and use these to investigate correlation between the recorded movement patterns with space weather events such as, for example, sun cycles and geomagnetic storms. Species or taxon specific differences will be assessed, and mechanisms through which space weather could influence the movement of marine mammals will be explored.

The position is funded for 24 months through a NRF South African National Antarctic Program Postdoctoral Grant at the University of Pretoria (Pretoria, South Africa) and will work closely with the South African National Space Agency (Hermanus, South Africa). Project start date is negotiable, but aiming to start as soon as possible.

We are looking for a self-starting, independent and highly motivated colleague who is interested in marine mammal movement ecology, space weather, habitat modelling and science communication. PhD required, with background in either ecology/zoology/physics. Skills in statistics, and GIS; competency with GIS and R/Python/Matlab is essential; strong writing skills, ability to adapt/learn quickly are a major plus. Ability to work in Hermanus for at least part of the project is a plus as well.

If you have questions or are interested in the position, please email Dr Mia Wege at mwege@zoology.up.ac.za and attach your CV.

Position will be open until filled.

The project involves collaboration between the Mammal Research Institute (MRI) at the University of Pretoria and the South African National Space Agency (SANSA). The project will be led by Dr Mia Wege, working closely with a team of experts in their respective fields (Dr Els Vermeulen (MRI), Dr Pierre Cilliers (SANSA), Dr Stefan Lotz (SANSA), and Prof Nico de Bruyn (MIMMP - MRI)).

A new field year, a new team.

In April three new team members set sail for the sub-Antarctic where, for the next 14 months, Marion Island will be their home.

New sealers Michael Ross (second from left), Banele Dosi (center) and killer whaler Monica Leitner (third from right) head out on their first walk on the island accompanied by the previous year’s team © Rowan Jordaan.

This rugged island, only 25 km long and 17 km wide (290 km2 in area), is accessible only to researchers, who visit the island for 14-month stints to study the fauna and flora that call the island home. Many of the marine mammal and bird species spend most of their lives at sea foraging in the Southern Ocean, coming to the island only to breed and moult.

After arriving late in the month, the two new sealers, Banele Dosi and Michael Ross, and Killer whaler, Monica Leitner had to wait patiently for the weather to clear enough to allow the helicopters to fly off the S.A. Agulhas II before their adventures could begin on the island. Located in the infamous “roaring forties”, the island weather can shift suddenly from sunshine, to ice pellets, to rain and snow, all accompanied by predominating gale force winds. It is a harsh but magnificent landscape.

The sealers exercise their Marion knees as they head up from the beach at Macci bay © Yinhla Shihlomule.

After several days the team was flown onto the island, where for the next month they would be taught what their positions entail and learn the tricks of the trade from the previous team members during take-over. After this period the old team would head back to the South African mainland leaving the three new members, along with the rest of the M79 team, on the island until next year April.

During their time on the island the team will be responsible for collecting long-term monitoring data from the region’s top predators; southern elephant seals, sub-Antarctic fur seals, Antarctic fur seals and killer whales. This crucial data allows researchers to study the response of these animals to environmental change in the region.

Caitlin van der Merwe’s excitement is palpable as she finally explores her study site © Yinhla Shihlomule.

Joining the team for only the take-over period, MIMMP MSc student, Caitlin van der Merwe, also has the opportunity to familiarize herself with her study species. Caitlin is currently working with elephant seal tracking data to look at the at-sea behaviour of intermittent versus continuously breeding female southern elephant seals and the environmental conditions that impact this. With this project building on her previous desktop-based Honours work on the same species it is especially exciting for Caitlin to finally see her study site!