The sharks in the Gulf of Mexico have a hunting timetable. We previously thought that all sharks hunted at around the same time – dusk or dawn – but it turns out that different shark species sharing the same space have their own scheduled times for foraging. This might help them share resources and avoid one another.
This was unexpected, so she and her colleagues looked more closely at whether different species were partitioning their foraging times. They found that different shark species with overlapping diets share resources by foraging at different times each day.
It was a surprising discovery, as this type of time-based resource division isn’t thought to be common in nature, says Lear. “Very few instances of time partitioning on a daily scale have been observed,” she says. “However, this could be more common than we think in marine ecosystems, which haven’t been widely studied in this way because tracking and observing underwater animals can be more difficult.”
Lear and her colleagues looked at the foraging behaviour of six coastal shark species. They tagged a total of 172 individual animals with acceleration data loggers, then monitored their activity levels over time, obtaining 3766 hours of data.
Bull sharks (Carcharhinus leucas) were most active in the early morning, while tiger sharks (Galeocerdo cuvier) were out more during midday. Afternoons were for sandbar sharks (Carcharhinus plumbeus) and evenings for blacktips (Carcharhinus limbatus). Both scalloped hammerheads (Sphyrna lewini) and great hammerheads (Sphyrna mokarran) were most active during night hours.
“It looks like the bigger species – the tiger sharks – have their time and no one interferes with it, so they hunt whenever is best for them,” says Georgia Jones at Bournemouth University in the UK. “Then smaller species like the blacktips will work around the times so that they’re not co-occurring with the tiger sharks, because tiger sharks will predate them.”
Journal reference: Proceedings of the Royal Society B: Biological Sciences, DOI: 10.1098/rspb.2021.0816
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