Climate change is pushing marine animals towards the poles and setting threatened species on unpredictable collision courses – a point illustrated by a new report on great white sharks produced by Monterey Bay Aquarium in the USA.
Increasing numbers of juvenile white sharks have been turning up in California’s Monterey Bay in recent years, and aquarium researchers have analysed data collected through electronic tagging over the past 20 years to determine how climate change has altered the animals’ behaviour.
Last August water temperatures in the bay reached as high as 21 degrees C, compared with an average of 13 degrees. Temperature extremes have become familiar in the area since a heatwave that lasted from 2014 to 2016.
This was accompanied by unprecedented numbers of juvenile white shark sightings, say the researchers – and a related fall in populations of shark prey such as salmon and sea otters, the latter a threatened species important to the local ecosystem. Young sharks at first eat fish and then practise their hunting skills on the otters before graduating to seals and sea-lions.
The team analysed 22 million electronic data records from 14 sharks tagged in southern California and Mexico and compared them to 38 years of ocean temperatures to chart how young great whites are being drawn to warmer waters some 370 miles north of their previous range.