Hurricanes Harvey and Irma caused massive destruction across the Texas and in Florida — millions of people were displaced; lives were lost, and homes were destroyed, even though modern forecasting technology gives us ample time to board up windows, stockpile supplies, or flee to safer ground. That’s just how powerful those storms were.
But what about the creatures beneath those raging seas? Do sharks, for example, know what’s coming? And if so, do they flee, go deep, or ride out the storm Lt. Dan-style?
It turns out sharks do know when a hurricane is approaching. These fish have organs called lateral lines, rows of small pores connected to a fluid-filled canal along each side of their bodies, which sense small changes in pressure. Sharks normally use this organ to pick up the thrashings of wounded or sick fish and other prey, but it also can detect drops in air pressure that indicate an approaching hurricane.
A 2001 study at Florida’s Mote Marine Laboratory documented young blacktip sharks leaving the shelter of shallow water nurseries and heading for deeper water following the dramatic drop in barometric pressure preceding a hurricane. The youngsters returned to their usual hangouts once the storm passed. Scientists have observed similar behavior in juvenile lemon sharks.
Large adult sharks also appear to deliberately avoid storms, according to Nick Whitney of OCEARCH Global Shark Tracker. The organization’s GPS trackers have shown big, ocean-going sharks such as great whites diving into deeper waters or leaving the path of approaching hurricanes.
Dolphins and whales sense changes in the salt concentration of water near the sea surface caused by heavy rainfall and have been reported leaving an area experiencing the downpours common on leading edges of hurricanes. However, these marine mammals can drown when surfacing to breathe in the turbulent water of severe storms, and that could be the case for other air-breathing marine life such as sea turtles. Hatchling and juvenile sea turtles can’t go as deep as adults and may be at greater risk. Whales can remain submerged for more than an hour and sea turtles for four or more hours when resting, but eventually these animals must surface to breathe and face the rough seas and blowing spray.
That said, Donna Shaver, chief of the Division of Sea Turtle Science and Recovery at Padre Island National Seashore in Texas, has tracked adult sea turtles that apparently did not bother to leave the area when a hurricane came through. Shaver reports that Kemp’s ridley sea turtle nests on the Texas coast in spring and early summer, but fortunately nesting season had ended before Harvey arrived. A tagged Kemp’s ridley named Kimberly apparently remained on the west coast of Florida during Irma.
In addition to violent surf and changes in salinity, large storms also reduce the levels of dissolved oxygen in ocean waters. Any of these conditions can kill fish and crabs and sea creatures that cannot move, such as oysters, according to the University of Miami Rosenstiel School of Marine and Atmospheric Sciences.
In addition, heavy rain during hurricanes lowers temperatures at the water surface and turbulence mixes layers of seawater normally stratified by temperature and salinity. Hurricanes also create waves five feet or higher and strong currents as deep as 300 feet. While larger, more mobile animals probably handle these changes relatively well, it’s safe to say Harvey and Irma took other marine creates for quite a ride.