A new study found that sharks born into environments degraded by human-induced stressors develop more slowly than those who grow up in more pristine habitats.
The Centre of Excellence for Coral Reef Studies at James Cook University found that human-related factors such as climate change could impede the condition and growth rate of newborn reef sharks after studying populations in St Joseph atoll and the island of Moorea.
St Joseph is an uninhabited, remote and small atoll in the outer islands of Seychelles, where no environmental changes happened at the time of the study. Moorea is a popular tourist destination in the French Polynesian Islands—one that is still recovering from a loss of up to 95 percent of its live coral cover.
“We found that although shark pups are born larger, heavier and better conditioned in Moorea, they soon lost their physical advantage over the pups in St Joseph,” Dr. Jodie Rummer, who co-authored the four-year study, said.
The study analyzed the size and diets of 546 young reef sharks caught in the two sites and found that despite the Moorea population being born larger, the advantage was short-lived.
“Bigger mothers give birth to bigger babies, which is what happens in Moorea,” Dr. Rummer said. “But that doesn’t necessarily mean the babies will eat and grow quickly after that.”
Despite being smaller and lighter for their size, the pups from St Joseph started foraging for food earlier in life and became more successful predators than their Polynesian counterparts. The authors attribute the bigger pups losing their physical advantage because Moorea was experiencing a degraded quality and quantity of prey, coupled with human-induced stressors such as over-fishing, climate change and coastal development.
“Sharks are at risk from human-induced stressors because they may not be able to adapt fast enough to keep pace with the changes that are happening in their environment,” Dr. Rummer said. “Not enough generations are being born fast enough to make the genetic changes to adapt to what’s going on in their habitats.”