Adult male and female Weddell seals (Leptonychotes weddellii) were fitted with Time-depth (TDR) and Stomach temperature recorders (STR) at Drescher Inlet (Riiser Larsen Ice Shelf), eastern Weddell Sea coast, between January and March 1995. Ten of 15 data sets were selected for analyses to investigate the seals' haul-out and underwater activity patterns in relation to the tide (doi:10.1594/PANGAEA.511417, doi:10.1594/PANGAEA.511426, doi:10.1594/PANGAEA.511428, doi:10.1594/PANGAEA.511430, doi:10.1594/PANGAEA.511432, doi:10.1594/PANGAEA.511441, doi:10.1594/PANGAEA.511444, doi:10.1594/PANGAEA.511450, doi:10.1594/PANGAEA.511452, doi:10.1594/PANGAEA.511472). These data sets provided simultaneous dive depth and stomach temperature records of five seals. Diving and temperature data were analysed with the help of time series analyses tools. We identified a half-day (semicircadian) rhythm in underwater activity and body temperature. A close correlation was found between the rhythmicity of the tide and the timing of the seals' underwater activity and oscillations of their body temperature. We propose that the tide is the principal zeitgeber for the Weddell seals' ultradian cycle of behaviour during the austral summer. Another seven data sets did not match with the requirement of synchronous dive depth and stomach temperature recordings (doi:10.1594/PANGAEA.511451, doi:10.1594/PANGAEA.511429, doi:10.1594/PANGAEA.511446, doi:10.1594/PANGAEA.511447, doi:10.1594/PANGAEA.511448). A total of 13 Weddell seals were immobilised during the study period using a combination of ketamine, xylazine, and diazepam. Eleven seals were drugged once, and two were drugged two times, coming to a total of 15 immobilisation procedures. Narcoses were terminated with yohimbine (doi:10.1594/PANGAEA.438927).

Supplement to: Bornemann, Horst; Mohr, Elmar; Plötz, Joachim; Krause, Gunther (1998): The tide as zeitgeber for Weddell seals. Polar Biology, 20(6), 396-403