It could be, think there may be a reference to it in cesar milan's book, 'cesar's way.' about dog behaviour. My dogs also do it, not often, but it is like a wolf howl, i think its when they think they are alone and are calling for their 'pack' although quite how this would relate to yours on the beach knowing you were near and 'you are his pack' as such, is not clear. One of mine previously used to do it after aircraft passed over we are near a MOD training area and get loads coming over low and it hurts their ears. I saw one of mine stood in the doorway of the open garage and he lifted back his head and did it yesterday, but why I am not sure, he was on his own in that part of the garden but the others were in the rear bit so he wasn't alone, as such - one recently did it in the middle of the night although he was sleeping with his sibling on the quilt next to him. maybe you can google it., too?