Northern anchovies are seen as they break the surface to escape predators from below. This telegraphs their presence to predators from above. They can't win.
Engraulis mordax school jumping at surface 2014 09-10 SB Channel-b-006
A curious image of some real biological interest: A Humpback Whale (Megaptera novaeangliae) lets out a big blast of air bubbles from its blowhole as it rises up from below this patch of kril (Thysanoessa spinifera). You can see the krill jumping out of the water.