A tornado of fish 10,000 strong spins in shallow water in the Bahamas. Occasionally, flashes of silver break from the pack as fish shoot to the surface, gulping air and slicing back through the water. This is the pre-spawning behavior of the bonefish, a popular quarry for anglers off the coast of Florida and in the Bahamas. Researchers presented their observations of this secretive behavior to the Bahamas Ministry of the Environment and conservation collaborators' Bahamas National Trust and The Nature Conservancy.
The bone-fish is worth hundreds of millions of dollars a year to the recreational fishing industry, but it is threatened due to loss of habitat and overfishing by net-trawling methods. Fish ecologist Andy Danylchuk, of the University of Massachusetts Amherst, and Aaron Adams, director of operations for Bonefish & Tarpon Trust at the Florida Institute of Technology, tracked 10,000 bonefish in their final stages of spawning using tracking tags inserted into some members of the school.
The fish normally hang out near the sea bottom of shallow offshore waters, perhaps 30 feet (10 meters) down. But right before spawning, in mid-afternoon, the school rose into a silver spiral, and fish occasionally broke the surface, an unusual behavior for bone-fish. As night fell and the moon rose, the fish started to move from the shallows to the reef edge, where the seafloor drops off suddenly. As Danylchuk and Adams watched, the fish descended 160 feet (50 m) and hovered about a quarter-mile (0.4 kilometers) from the drop-off, suspended over thousands of feet of dark water.
After waiting in place for about an hour, the school suddenly rushed to the surface, where they released eggs and sperm into the water. The fish then broke for shallow water again, leaving behind millions of fertilized eggs drifting on the ocean currents. "This new understanding of bonefish movement and spawning aggregations has significant implications for their conservation," Danylchuk said. Previous conservation attempts had focused on the typical shallow-water bonefish habitat. But fish migrate long distances to form huge spawning schools, and they spend this crucial time in deep waters, according to both the new observations and a study by the same scientists of the fish spawning. The findings point to the need to consider both deep and shallow habitats in conservation plans.