Blacktip sharks usually travel in the tens of thousands from North Carolina to Florida. Recently, however, just one-third of this population is migrating south to warmer waters. Male sharks usually leave during the cooler winter months and return when it’s warmer in the spring to mate with females. But warming waters seem to be changing this behavior. This could have serious, negative effects upon Florida fisheries. “These traveling sharks keep Florida’s coastal ecosystem healthy by weeding out weak and sick fish, and thereby helping to preserve coral reefs and seagrasses.”
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Over the past decade, the North Atlantic’s salinity has been decreasing. It is not known whether this phenomenon is due to an influx of freshwater from ice or land or whether it is the result of some other natural, long-term cycle. Researchers attribute the immediate cause to changes in ocean circulation. But they warn that further decline in salinity—from Greenland’s melting glaciers—“could impact fish stocks and the ocean’s ability to absorb CO2.”