Climate change is making sharks ‘right-handed’

Warming oceans are changing the way sharks swim – and making them right handed, researchers have found.

Australian scientists incubated eggs in tanks heated to simulate temperature changes at the end of the century.

They found half died within a month, and those who survived became ‘right handed’, preferring to swim to the  right, a process known as lateralization.

The researchers found the rising temperatures developed the trait far more quickly than they expected.

‘We incubated and reared Port Jackson sharks at current and projected end-of-century temperatures and measured preferential detour responses to left or right,’ the researchers wrote in a study published in the journal Symmetry.

To test whether the sharks had developed lateralization, the team placed them in a long tank with a Y-shaped partition at one end. 

Behind the partition was a food reward; sharks just had to decide whether to swim to the right or left side of the Y to reach their snack.

‘Sharks incubated at elevated temperature showed stronger absolute laterality and were significantly biased towards the right relative to sharks reared at current temperature.’

The researchers say the changes show that climate change could have a far greater, and faster, effect on marine brains than thought. 

‘Climate change is warming the world’s oceans at an unprecedented rate,’ they wrote.

‘Under predicted end-of-century temperatures, many teleosts show impaired development and altered critical behaviors, including behavioral lateralisation. 

‘Since laterality is an expression of brain functional asymmetries, changes in the strength and direction of lateralisation suggest that rapid climate warming might impact brain development and function.’    

Researchers collected a clutch of Port Jackson shark eggs from the waters off of eastern Australia. 

They incubated 12 eggs in a tank warmed to the current ambient temperature of the bay (about 70 degrees Fahrenheit, or 20.6 degrees Celsius) and 12 others in a tank that was gradually warmed to 74.5 degrees F (23.6 degrees C) to simulate those predicted end-of-century ocean temperatures.

Five sharks incubated in the elevated temperatures died within a month of hatching.

DO SHARKS HAVE BEST FRIENDS?

For the first time, researchers have shown that sharks show very strong preferences for particular individuals in their social networks over years, and prefer to hang out with others of the same sex and size.

The study, which involved tagging Port Jackson sharks (Heterodontus portusjacksoni), was conducted in Jervis Bay in New South Wales, Australia. 

The bay was chosen because it hosts large seasonal mating aggregations of Port Jackson sharks, a bottom-dwelling species endemic to Australia, where both males and females migrate yearly from their foraging ground in southern Australia to return to the same reef in Jervis Bay to breed.

Locations of acoustic receivers deployed in Jervis Bay (NSW, Australia); each circle represents a receiver 

Proximity loggers were attached to seven individual sharks in 2012, and acoustic receivers, fixed either to the seafloor or to mooring lines in mid-water, allowing for the remote tracking of marine life in three dimensions, were deployed in 2012 and 2013.  

The researchers found that when the sharks return to their breeding reefs, they do so with incredible accuracy. 

The Fish Lab at Macquarie University studies these shark social interactions by using acoustic tags that identify individual animals when they are within range of a receiver.

By analyzing the time-stamps of these receivers, the researchers can tell who hangs out with who and for how long.