Shark divers can expect more opportunities to encounter tiger sharks in waters such as those off the north-eastern USA – as a result of climate change.
It seems that the locations and timing of the sharks’ migrations in the North Atlantic have been changing rapidly as a result of rising ocean temperatures, according to a new study led by scientists in Florida.
But the climate-driven changes to their habits have also left tiger sharks (Galeocerdo cuvier) more likely to find themselves outside protected areas and so more vulnerable to commercial fishing, say scientists at the University of Miami (UM) Rosenstiel School of Marine & Atmospheric Science.
The team employed satellite tracking of the sharks over nine years to record their migrations as these extended further towards polar regions. They combined this data with nearly 40 years of tag-and-recapture information from the National Oceanic & Atmospheric Administration (NOAA) Co-operative Shark Tagging Program, along with satellite-derived sea-surface temperature data.
The analysis revealed that the sharks are being driven to northern areas earlier in the year during particularly warm periods, decreasing their protection from fishing in the process. Other possible consequences were disruption of their feeding and increased encounters with human water-users, including scuba divers.
Seas off the north-east coast of the USA that were traditionally too cold for tiger sharks have warmed so much in recent years that they can now support what are the biggest cold-blooded apex predators in tropical and warm-temperate seas.
Over the past decade, the warmest on record for ocean waters, tiger shark migrations have extended around 400km further poleward for every 1°C increase in temperature above average. The sharks are also migrating about 14 days earlier to waters off the north-eastern USA.
“Tiger shark annual migrations have expanded poleward, paralleling rising water temperatures,” said Neil Hammerschlag, director of the UM Shark Research & Conservation Program and lead author of the study, which has just been published in the journal Global Change Biology.
“Given their role as apex predators, these changes to tiger shark movements may alter predator-prey interactions, leading to ecological imbalances, and more frequent encounters with humans.”
17 Jan 22
