I assume populations were larger, but were sightings more common? What superstitions might a peaceful Dane attach to them? Any practical use for a sighting? My understanding is that whaling was starting to be a thing, but not much of an industry yet. I'm curious what non-viking Scandinavians of the "Viking Age" thought anout these great monsters of the ocean.
My understanding is that whaling was starting to be a thing, but not much of an industry yet.
I basically agree to your understanding, and I have to apologize in advance that to estimate the historical (especially pre-1500) population of whales in the North sea region as well as the frequency of their sight is beyond my ability.
+++
Ælfric's Colloquy, a Latin textbook for the monks written by Abbot of Eynsham about a thousand years ago in the midst of the Late Viking Age England, indeed mention the interesting passage on the fishing and possible commercial whaling:
- Teacher: What do you catch in the sea?
(ll. 61-70, the translation is taken from:Ælfric's Colloquy, trans. Ann E. Watkins)
On the other hand, Norwegian Ohthere (usually rendered as Ottar in modern Norwegian)'s account on the coastal life of northernmost part of Norway is another 10th century evidence of whaling in the North Sea:
'......the best whale hunting is in his [Ohthere's] own land: they [whales] are forty-eight ells long and the biggest fifty ells long; he [Ohthere] said that he and six others killed sixty of them is two days' (Translation is taken from: Nordeide & Edwards 2019: 10).
These two accounts are all of the contemporary written evidence of whales and possible whaling in the Viking Age Northern seas. Norwegian and Icelandic lawbooks are often cited as evidence of drifted whales in the Viking Ages, but they were firstly written in the 12th century or further later (the manuscript is dated to the middle of the 13th century).
Nevertheless, while neither of the texts allude to the concrete use of which body part of the whale, it is worth noting that both texts suggest the whale hunting in the 10th century have already been a (group) commercial business. Ottar's unbelievable whaling result surpassed much more than the amount of the single or a few farmstead could consume (though it is clear that we cannot take the number he caught as narrated in the description at face value), and the teacher mentions the great profit that the group whaling (with several boats) could yield.
Ælfric's text also presuppose that even the young English monks in the monastery probably had heard about many fishes and sea animals, including whales and dolphins.
Ælfric also warns us about the possible danger of whaling, however, so if OP had only insufficient equipment for fishing/ whaling and see whales on their way to the land, it would probably wise to leave them in peace.
+++
What superstitions might a peaceful Dane attach to them?
The closest evidence we have is from 13th century Norway, so it was written more than 2 centuries later than OP had allegedly lived (as well as the Christianization of Scandinavia) that we have some uncertainty about to what extent the lore of whales narrated in the text could date back further to the 10th century, the transition period from pre-Christian polytheism to Christianity.
The Old Norwegian text in question is called King's Mirror, a pedagogic text originally written for the education of princes in the royal court in the middle of the 13th century. This text mention about a dozen of whales and dolphins in the ocean near Iceland and Greenland, so I pick up some of them (and related lore) below (Larson trans. 1917: 119-24):
References:
+++