Warming oceans due to the climate crisis are having a significant impact on the migratory patterns of tiger sharks, allowing the apex predator to expand its range, but also exposing them to new risks, a new study has warned.
Research by scientists at the University of Miami has found both the location and timing of tiger shark migrations have changed as the world’s seas have warmed, increasingly moving them out of protected areas outside of protected areas, where they are more vulnerable to commercial fishing.
The tiger shark is the largest of the predatory sharks, with adults occasionally exceeding 7.5 metres (24.6 feet) in length, but industrial fishing and hunting by humans has seen their numbers collapse, with the species now listed as near threatened.
While waters off the US northeast coastline have historically been too cold for tiger sharks, temperatures have warmed significantly in recent years making them increasingly suitable for the species, the researchers said.
“Tiger shark annual migrations have expanded poleward, paralleling rising water temperatures,” said Neil Hammerschlag, director of the University of Miami Shark Research and Conservation Programme and lead author of the study.
“These results have consequences for tiger shark conservation, since shifts in their movements outside of marine protected areas may leave them more vulnerable to commercial fishing.”
The research comes as the latest data reveals the world’s oceans are hotter than ever, with temperatures breaking records for the sixth year in a row.
Dr Hammerschlag and the research team discovered the changes to the sharks behaviour by analysing nine years of tracking data from satellite tagged tiger sharks, and combining this with nearly forty years of conventional tag and recapture information supplied by the National
Oceanic and Atmospheric Administration (NOAA) Cooperative Shark Tagging Programme.
They also used satellite derived sea-surface temperature data to come to the conclusion the migratory expansions were driven by the climate crisis.
The researchers said that during the last decade, when ocean temperatures were the warmest on record, for every one-degree Celsius increase in water temperatures above average, tiger shark migrations extended farther poleward by roughly 250 miles (over 400 km) and sharks also migrated about 14 days earlier to waters off the US northeastern coast.
They warned their findings could have significant implications for some ocean ecosystems and mean the sharks come into increased contact with humans.
Dr Hammerschlag said: “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.”
The research is published in the journal Global Change Biology.
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