Here I tried to merge two tracks in Audacity.
Again I read too fast! One day, I will learn.
I shifted the gain to -8dB on the whalesong noises, with lots of fade-in/fade-out effects in combination to keep the whales from honking over the poem. The downside of both fade in and fade out is that they begin (or end) with silence, so you have to be prepared to snip those bits of the track off in order to get a more even sound.
The biggest thing that made this messy was that I tried to combine the background underwater noise and the whalesong itself on the same track. This makes it difficult to move, clip, and adjust all of the sound elements independently. Rookie mistake.