ANCHORAGE, Alaska — Researchers off Mexico’s Pacific coast are observing what they say could be a case of global warming’s effects in the far north: gray whales returning to calving grounds malnourished. Layers of fat should have covered whales’ spines last winter, but instead researchers saw vertebrae sticking out. They spotted other signs of malnutrition – depressions around the blowholes and head, and protruding shoulder blades – that may indicate declining health. At least 10% of gray whales returning to Laguna San Ignacio, 1 of 4 main calving and breeding lagoons off Baja California, Mexico, showed signs of being underfed. That’s according to Steve Swartz, a National Marine Fisheries Service whale expert based in Silver Spring, Maryland. Researchers are trying to find out if it’s a warning sign that climate change in the North Pacific is affecting the tiny crustaceans the whales suck up from the ocean floor, and if switching to alternative prey will affect their well-being.