The light. This is the biggest difference and the one people underestimate. On 3 January the boat leaves in darkness, spends four hours in a dusk the colour of a bruise, and comes home in darkness. On 20 February the same boat leaves in a blue morning, spends the middle of the day in flat gold light off the snow, and comes back at sunset. Photographers argue about which is better. Everybody else finds February easier to enjoy.
Where the boats go. In December and early January the herring sit in the fjords around Skjervøy, two hours north of town, which is why eight of the fourteen listings here drive you there and back. As the schools loosen through late January, crews range wider and the full-day trips at $361 and $340 get more out of their twelve hours than the six-hour boats do.
How many people are with you. The last week of December and the first week of January are the busiest of the Arctic winter. By the first week of February the same boat sails with room on the rail, the guides have time for questions, and the small listings like $218 and $282 become genuinely intimate.
What stays the same: the suits, the hot drinks, the crews, the free cancellation to twenty-four hours before, and the fact that a whale watching Tromso trip in either month is a full day rather than an excursion.