It is death by 1000 cuts Monty; hunger certainly will be a contributing factor to these strandings, with offshore species (such as pilot whales) driven inshore in search of food, then getting trapped/disoriented in the shallows and stranding as a consequence.
To use this sonar equipment next to a marine sanctuary is unacceptable, even if the effects of this activity are not fully understood (invoke the precautionary principle). It defeats the purpose of establishing the sanctuary, especially should it have been established to protect a unique area/flora/fauna (I don't know the politics/rationale behind this sanctuary). Moreover, I don't know the size of the sanctuary, but should it be small, centred on these islands, then there could well be an inadequate buffering area around it to protect what lies within from the effects of active sonar, rendering the effect of any possible sonar activity in the region immediate and long-lasting (I would like to see whether this activity has any effect on species of non-charismatic nature ... like what the fisherfolk refer to as 'bottom filth', the myriad inverts at the bottom of the food chain).
My understanding of a US sanctuary is that they are not reserves, but some level of extraction is permitted from them (i.e. fishing). Is this correct?