Methodology:

From January 1998 to December 2023 sightings of wildlife around Rothera Research Station were recorded opportunistically. Observers included station scientists on oceanographic sampling trips, those undertaking a formal seal-watch prior to SCUBA diving operations, together with interested station personnel on recreational walks. These handwritten records were collated in monthly spreadsheets.

An absence of marine mammal sightings means one of two things; 1. observations were made but no marine mammals were seen, or 2. no observations were made. A day with no marine mammal sightings but records of birds was assumed to be a true zero (1), whereas a day with no records of either birds or marine mammals was coded as a missing value NA (2).

From January 1998 to December 2014, the largest single count per species per day was recorded in the spreadsheet. However, in January 2015, to smooth out the noise, there was a switch from recording daily observations to weekly presence/absence data, together with the maximum number of each species observed during that week. This also reduced the impact of the same individuals being counted multiple times by different observers.

To ensure comparability between data collected quasi-daily (pre-2015) and weekly (January 2015 to December 2023), the maximum count for each species per week was calculated. For those weeks which spanned two months, the week was assigned to the month with the larger number of days in that week.

Daily assessments of sea ice were made from Rothera Research Station by visual inspection. The area coverage was scored from 0 (no ice present) to 10 (complete coverage of Ryder Bay). To enable comparison with the marine mammal observation data, the maximum score was calculated for each week of the study period.

The marine mammal observations and ice data were recorded at Rothera research station by the Assistant Marine Biologist: Alice Chapman (winters 1997, 1998), Jenny Beaumont (1999, 2000), Raynor Piper (2001, 2002), Andrew Miller (2003, 2004), Paul Mann (2005), Helen Rosetti (2006), Alison Massey (2007, 2008), Terri Souster (2009, 2010), Simon Reeves (2011), Mairi Fenton (2012), Sabrina Heiser (2013, 2014), Samuel Pountney (2015), Sarah Reed (2016), Zoë Waring (2017, 2019), Marlon Clark (2018), Emma Bolton (2020), Ryan Matthews (2021), and Alice Clement (2022). From 2023 marine mammal sightings have been undertaken and collated by the Ocean Scientist: Emma Stuart (2023). In addition marine mammal observations were also recorded by interested station personnel, and particularly by Clem Collins (Rothera Air Unit Assistant).

Data collection:

Data processed using R (version 4.4.2).

Data quality:

Volunteer-collected observational data has its limitations, with the following impacting data quality and variability:

-The accuracy of species identification depends on the observer's experience. For this dataset, this will have varied hugely.

-The number of individual animals recorded may be rough estimates. The greater the number recorded, the less accurate the estimate is likely to be.

-There will have been variability in whether observers were using a telescope, binoculars, or the naked eye. This will not have been recorded.

-Recording effort varies hugely at every timescale. This relates to how long an observer spent outside observing, but also how many different people completed recording sheets on any particular day, week, or month. This is influenced by the number of people on station on any given day (there are far more people on Station in summer than in winter), the daylight hours available to make observations (the sun doesn't rise for six weeks during midwinter), whether the weather encouraged people to spend time outside, amongst other factors.

Certain weeks or even months have no data at all. This may be due to no-one completing a recording sheet during that month, or because recording sheets were lost before being input to the spreadsheet.