Large sharks exhibit varying behavioral responses to major hurricanes

Abstract

Under global climate change, storm events are predicted to increase in strength and frequency. Although aquatic animals can be affected by acute natural disturbances, information on the immediate consequences of these weather systems on the behavioral ecology of highly mobile aquatic predators remains limited. Here we examine the spatial distributions, activity spaces, and ecological change-points of four large shark species (mean: 193 cm fork length ± 70 SD) via passive acoustic telemetry in two different locations in the subtropical Atlantic (Little Bahama Bank, Bahamas, and Biscayne Bay, Florida, USA) in relation to two separate major hurricane events (category 4 and 5). We tested whether sharks would evacuate shallow coastal habitats (and thus exit the acoustic arrays) during the hurricanes and exhibit comparable size of activity spaces pre- and post-storms, as has been previously found for smaller (50–150 cm fork length) sharks elsewhere. Located on the northwest edge of the Little Bahama Bank, Bahamas, an acoustic array consisting of 32 acoustic telemetry receivers tracking tiger sharks Galeocerdo cuvier sustained a direct hit from Hurricane Matthew in 2016. Daily detections of tagged tiger sharks within the array were consistent before and during the hurricane. Immediately following the storm, daily tiger shark detections approximately doubled. Size and extent of tiger shark activity space within the array were consistent pre- and post-storm. Located off Miami, within Biscayne Bay, an array of 32 acoustic receivers tracking bull Carcharhinus leucas, nurse Ginglymostoma cirratum, and great hammerhead sharks Sphyrna mokarran was exposed to tropical-storm-force winds from Hurricane Irma in 2017. As the eye of the storm passed 140 km to the west, most sharks previously present in the array were no longer detected, while two nurse sharks remained at receivers near Miami. Numbers of tagged bull sharks declined following Hurricane Irma, whereas other species did not. Ecological change point analyses indicated that seasonal changes - rather than storm conditions - cannot be ruled out as the primary driver of post-storm shark behavior. Unlike smaller shark species which have previously been found to evacuate shallow water habitats during storms, we found variable responses of large sharks to storm events.