Magdalenians did eat sea mammals.

M.P. Richards et al, Isotope evidence for the intensive use of marine foods by Late Upper Palaeolithic humans. Journal of Human Evolution, 2005 (pay per view).

Abstract

We report here on direct evidence for the intensive consumption of marine foods by anatomically modern humans at approximately 12,000 years ago. We undertook isotopic analysis of bone collagen from three humans, dating to the late Palaeolithic, from the site of Kendrick's Cave in North Wales, UK. The isotopic measurements of their bone collagen indicated that ca. 30% of their dietary protein was from marine sources, which we interpret as likely being high trophic level marine organisms such as marine mammals. This indicates that towards the end of the Pleistocene modern humans were pursuing a hunting strategy that incorporated both marine and terrestrial mammals. This is the first occurrence of the intensive use of marine resources, specifically marine mammals, that becomes even more pronounced in the subsequent Mesolithic period.

Not exactly breaking news but unknown for me to date. It relates and seems to confirm what I already commented in Magdalenian and Inuit harpoons a month ago: they were used for seal hunting or whaling, just as Inuits did until very recently.