"Watching for Dolphins" is heavily enjambed. In fact, of the poem's 36 lines, only are end-stopped. This intense use of enjambment has several noticeable effects.
First off, the use of enjambment encourages the reader to keep moving forward—resulting in a sense of perpetual motion, of ever-building anticipation. In the first stanza, for example, all six lines are enjambed. Combined with the lack of punctuation (the first punctuation mark doesn't arrive until the middle of line 6!), this creates an initial sense of fluidity. There is a sense of the poem directing the reader's attention the way a film would, visually sweeping across the scene at hand.
Enjambment also creates a sensation of inevitability, of being pulled forward through the poem. This, perhaps, reflects the way that the passengers are pulled towards the bow by their intense desire to see the dolphins—figuratively speaking, the way that they are propelled forward by their deep longing to find a sense of meaning and purpose. The enjambment, then, is directly tied to the poem's sense of momentum. The ship is moving across the sea, bringing the passengers closer and closer to the end of their vacations. Enjambment gives the poem a sense of urgency; if the passengers are going to see dolphins and have some kind of life-changing experience in doing so, it has to happen soon. They are running out of time.
There is also a sonic element here. Although there are plenty of rhymes or near rhymes at the ends of lines, the enjambment keeps the reader from stressing those rhyming words too heavily (because there is no time for a pause at the end of the lines). This allows the reader to feel some of the anticipation and attentiveness of the passengers.
Finally, it's worth noting how enjambment interacts with caesura throughout the poem. Phrases and sentences regularly spill across line breaks, and indeed across the stanzas themselves, only to come to rest in the middle of later lines. As such, there are many commas, periods, and other punctuation marks that appear in the middle of lines. In a way, this might reflect the passengers' seesawing emotions—the way that their longing and desire builds and builds, only to be quickly quashed when no dolphins appear.