Dolphins followed our boat as we navigated the narrow stretch of sea that separates Cayo Santiago from the rest of Puerto Rico. They slid up to the surface, showed their glistening backs, and then dove back to the placid water. After a few minutes, they repeated the same maneuver, a bit closer to the boat this time. Their bodies sliced through the calm sea without any ripple, as if their slow jumps were just the occasional ebbs of the Caribbean Sea.
They blended perfectly into the marine environment that sometimes I forget that dolphins aren’t fishes. Instead of moving their tails sideways like their gilled neighbors, dolphins move their tails up and down, akin to the stride of a galloping horse. While fishes drop their eggs, spreading bubbles to the sea, dolphins suckle their young. In their distant evolutionary past, a dolphin ancestor, the mesonychidae, once lived inland–foraging in the shores of what is now Africa. Scientists suggest that this ancestral family lived close to the banks of rivers, feeding on mollusks and slow fishes. As the competition for resources grew fiercer, adaptive traits for catching faster fishes were selected for–slowly moving them to a more aquatic lifestyle and evolving a morphology fit to such an environment. Gradually, through millions of years, characteristics unfit for marine life were lost. The nostrils moved to the top of their heads to facilitate breathing, together with a host of other adaptive mechanisms, such as a fusiform body for fast swimming.
These dolphins have gone a long ways indeed. Yet, the years of evolutionary selection have not prepared them enough from the impact of human activities. Nathalie Ward of the Eastern Caribbean Cetacean Network (ECCN) reported that, “The growing exploitation of coastal resources, degradation of habitat, accidental capture, contamination, acoustic pollution and tourism are serious threats to whales and dolphins in the Wider Caribbean, which extends from the Gulf of Mexico, across the Caribbean, to the adjacent Atlantic.”
I stood up from the lancha as I watched the dolphins disappear from sight. They swam away towards the open ocean, breaking the surface once in a while, as we approached the dock of Cayo Santiago. They swam farther until their backs were like shadows of sea waves, completely unaware of that oil slick that drapes the seas of the neighboring Gulf of Mexico.