We have all heard stories of animals fleeing an area before a big storm of earthquake hits. This is because mobile species have the choice to move with changing environmental conditions to an area that is more suitable. Usually, these animals are land-based, but would ocean-dwelling species like sharks do the same thing? Now with over 500 shark species, the behavior has not yet been studied in all of them, but some interesting results have already been found in some species.
When the storm Gabrielle hit Florida in 2001, researchers (Michelle Heupel et al.) did not have time to remove the acoustic receivers that record data from tagged sharks. When they collected them after the storm, they noticed that the blacktip sharks left Terra Ceia Bay and moved towards deeper waters. This was unusual because the blacktip sharks were moving in large groups and it was not time for their migration yet. Furthermore, they left 7 hours before the storm hit!
The researchers thought this could be because of the dropping barometric pressure and bad conditions in the bay right before the storm hit. The sharks could probably detect the drop in barometric pressure using the highly sensitive mechanoreceptors within the inner ear that can detect subtle changes in hydrostatic pressure very accurately. The disturbance of the surface of the water would have been detected by the sharks vibration sense, mediated by the lateral line, which is also possessed by a few other fishes, including skates and rays. This system enables them to pick up vibrations of low frequencies and other disturbances.
Once the storm passed, the sharks returned to the area they were normally found in. The researchers were wondering if this was unique, or if more species showed this behavior. So when category 5 cyclone Yasi was bound to hit Queensland in 2010, they looked at the movements of 5 shark species. During the storm the receivers stopped recording data because of all the wave action. Because of this, it seemed like all sharks had left the area, but actually one species had stayed behind. This was the blacktip reef shark, which needs reefs to live on. The other species were coastal and therefore had the chance to leave. Again, after the storm, most sharks returned to the area.
Now since extreme weather will occur more often because of climate change, it is very important to study how sharks respond to that weather. Therefore more researchers are looking at how the weather is affecting the sharks movements and if climate change will be affecting their survival.
Michelle Heupel is currently involved in projects examining the long-term residence and movement patterns of inshore and reef predators including sharks, rays and large teleost fishes. This research will include defining how individuals use space in relation to human activities (i.e. fishing, marine park zoning, boating) and environmental change (i.e. response to salinity, temperature change or extreme weather events). Defining underlying mechanisms for movement is a key aspect of this research.