Tropical storms influence the movement behavior of a demersal oceanic fish species

Nathan M Bacheler,Robin T Cheshire,Kyle W Shertzer,Jamie H Macmahan

doi:10.1038/s41598-018-37527-1

Abstract

Extreme weather events strongly influence marine, freshwater, and estuarine ecosystems in myriad ways. We quantified movements of a demersal oceanic fish species (gray triggerfish Balistes capriscus; N = 30) before, during, and after two hurricanes in 2017 using fine-scale acoustic telemetry at a 37-m deep study site in North Carolina, USA. During storms, gray triggerfish movement and emigration rates were 100% and 2550% higher, respectively, than on days with no storms. We found that increased movement rates were much more strongly correlated with wave orbital velocity (i.e., wave-generated oscillatory flow at the seabed) than either barometric pressure or bottom water temperature, two covariates that have been demonstrated to be important for organisms in shallower water. Higher movement rates during storms were due to increased mobility at night, and emigrations typically occurred at night in the direction of deeper water. Overall, we found significant storm effects on the movement behavior of a demersal fish species in the open ocean, despite our study occurring in deeper water than previous studies that have examined storm effects on animal movement. We conclude that tropical storms are a driving force behind the structure of marine ecosystems, in part by influencing movements of mobile animals.

Highlights

Extreme weather events strongly influence marine, freshwater, and estuarine ecosystems in myriad ways
Despite being a demersal fish species in the coastal ocean, gray triggerfish strongly responded to two hurricanes whose eyes passed within 250 km of the study area
For fish that remained in the study area, movement rates nearly doubled during storms, and this increase was mostly due to increased movement rates at night, a time when gray triggerfish typically move very little[28]

Summary

Introduction

Extreme weather events strongly influence marine, freshwater, and estuarine ecosystems in myriad ways. Higher movement rates during storms were due to increased mobility at night, and emigrations typically occurred at night in the direction of deeper water. Physical changes to habitats and environmental conditions during and after storms influence marine organisms in myriad direct and indirect ways. Tropical storms can cause direct mortality of organisms[2], and indirect mortality via lack of dissolved oxygen or increased rates of disease due to degraded water conditions[3]. Moving away from storms can be costly even for mobile species in terms of the energy spent to migrate[11], increased mortality rates due to changes in habitat and community dynamics[12], and loss of reproductive and foraging opportunities. Other estuarine and coastal fish species such as smalltooth sawfish (Pristis pectinata) and blacktip reef sharks (Carcharhinus melanopterus) appear to be influenced by storms only minimally[16,17]

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Conclusion