How has James Reeves used aural imagery in his poem "In the Sea"?

I think you mean the poem "The Sea," by James Reeves. Aural imagery is imagery which appeals to our sense of hearing, rather than our sense of sight—so, the use of figurative language to create a vivid sense of place in terms of how something sounds. In this poem, Reeves uses aural imagery frequently so that the reader can almost hear the scene being described. Onomatopoeia, such as "rumbling, tumbling," creates sound pictures for us; Reeves also imagines the words the "dog" of the sea might be saying, such as "Bones, bones, bones!" Obviously, this is a continuation of the central metaphor: the sea is not really a dog, nor is it really speaking, but we understand that its "moans" bear some resemblance to these human words. They help us to create a mental picture of how the sea sounds. Likewise, the "hollos" of the sea on blustery days are accompanied by the onomatopoeiac "snuffs" and "sniffs" of the dog to create a rich tapestry of sound.
Reeves uses aural imagery, too, to describe quietude. When the sea is silent, the contrast of the dog who "scarcely snores" is drawn starkly—the absence of sound is almost as illustrative as the existence of it.

Imagery is description that uses the five senses of sight, sound, taste, smell, and touch. An aural image is a sound image.
In his poem "In the Sea," Reeves compares the sea to a dog. The great gray dog of the sea is sometimes hungry, sometimes restless, and sometimes calm and at peace.
Reeves uses sound imagery to help describe all three states of the doglike sea. When it is hungry, it makes sounds such as "clashing" its teeth, which would be a way to describe the crashing of waves. The sea/dog also "moans."
In the second stanza, the sea at night is compared to a restless dog. The winds that "roar" over the sea at night are likened to a dog that "howls."
Finally, the "reedy" sound of the calm sea is compared to the sound of a dog at rest, "quiet, so quiet," hardly snoring.
Whether these sound images work successfully is up to the reader to decide, but it is interesting to think of the sea as like a dog—frisky, howling, and quiet by turns.