Why baby sharks prefer swimming in shallow water

By Stephen Beech via SWNS

Baby sharks prefer swimming in shallow water, reveals new research.

Just like young humans, junior great whites prefer to stay close to the shore.

Now, marine scientists have shown for the first time that juvenile great white sharks select warm and shallow waters to gather within a few hundred yards of the coast.

They say their findings, published in the journal Frontiers in Marine Science, are important for conservation of the apex marine predators - especially as ocean temperatures increase due to climate change – and for protecting the public from potentially lethal attacks.

Baby great white sharks, known as pups, don’t receive any maternal care after birth, say scientists.

In the shiver studied off Padaro Beach near Santa Barbara, Calif., pups and juveniles gather in "nurseries" - unaccompanied by adults.

Study senior author Professor Christopher Lowe, of California State University, said: “This is one of the largest and most detailed studies of its kind.

"Because around Padaro Beach, large numbers of juveniles share near-shore habitats, we could learn how environmental conditions influence their movements.

“You rarely see great white sharks exhibiting this kind of nursery behavior in other locations.”

Prof Lowe and his team used darts to tag a total of 22 juveniles with sensor-transmitters.

The tagged sharks were both males and females aged between one- and six-years-old.

Previous research has shown that great whites can live for up to 70 years.

The sensor-transmitters measured local water pressure and temperature in real time, and tracked each shark’s position by sending acoustic ‘pings’ into receivers, spread along 5.5 sq kms (2.1 sq miles) of the shoreline.

The tracking was halted during the winter months, when juveniles temporarily left for offshore waters.

The research team gathered more data on the temperature distribution throughout the local water column using an autonomous underwater vehicle.

They then used artificial intelligence to train a 3D model of the juveniles’ temperature and depth preferences.

The results, published in the journal Frontiers in Marine Science, showed that the juveniles dived to the greatest depths around dawn and dusk, when they were likely foraging for skates, rays and other small bony fish.

They moved closest to the surface – between zero and four meters deep – in the afternoon when the sun was hottest, possibly to increase their body temperature.

Study first author Emily Spurgeon, a research technician in Prof Lowe’s team, said: “We showed that juveniles directly altered their vertical position in the water column to stay between 16 and 22 degrees Celsius, and if possible between 20 and 22C.

"This may be their optimum to maximize growth efficiency within the nursery.”

She said the results showed that the temperature distribution in the waters studied is ever changeable, which means that young sharks have to be constantly on the move to remain within the optimal range.

The team concluded that juvenile great white sharks spend most of their time in much shallower water than adults who were rarely seen in the nursery.

The findings also showed that the young sharks spread out at greater depths when seafloor temperatures were higher, but moved closer together towards the surface when deeper water was cooler.

The researchers still don’t know what benefits shark pups gain from gathering in nurseries in the first place.

But they believe one advantage might be to avoid predators.

Spurgeon said: “Our results show that water temperature is a key factor that draws juveniles to the studied area.

"However, there are many locations across the California coast that share similar environmental conditions, so temperature isn’t the whole story."

She added: "Future experiments will look at individual relationships, for example to see if some individuals move among nurseries in tandem.”