During Discovery Channel’s “Shark Week”, scientists seize the opportunity to provide some context to Discovery’s predominantly theatrical programming. Unfortunately, these television productions often focus on re-enacting ‘jaws-like’ attacks or producing fake documentaries about extinct sharks like the megalodon.
This year, to drum up interest in shark week in Canada, the Discovery Channel even fabricated a grainy video of a shark in Lake Ontario – a spectacle that got the Ontario Minister for Natural Resources to state, albeit skeptically, that people should be careful.
For the record, there are no man-eating sharks in Lake Ontario and no megalodons swim in our seas (I promise they are extinct!). Nonetheless, sharks do inhabit Canadian waters including 21 species in the Atlantic, 16 species in the Pacific, and up to 8 species in the Arctic. However, most Canadians are unaware that included in this list of Canadian sharks is a single visit by the current title holder of ‘world’s largest fish’ – the whale shark.
Whale sharks can grow up to 15 meters long and weigh 21 tons, which, in Canadian terms, is roughly 35 bull moose or 900 beavers. Unlike their Great White cousins, whale sharks are filter feeders with tiny, harmless teeth. In other words, whale sharks are only really a threat if you happen to be a floating small shrimp, a coral spawn, or a fish egg.
Besides their massive size, whale sharks are characterized by the unique patterns of white spots on their bodies, which can be used to identify individuals like human fingerprints.
Whale sharks don’t often stray from the warm, tropical waters between 23°C and 32°C – not exactly ocean temperatures in Canada. But on August 22 1997, a 10 meter long adult whale shark swam into the Bay of Fundy, which I assume looked like the picture above. In the Pacific, whale sharks have never reached British Columbia’s coast, as the northernmost record was a single whale shark sighted in northern California (PDF).
In the summer of 2012, a juvenile male whale shark was found dead in a salmon fishing net in the Sea of Okhotsk off northern Japan (PDF). Much like his Canadian comrade, the Japanese whale shark was likely drawn to the waters off Hokkaido because of unusually high sea surface temperatures that can promote blooms of their favourite planktonic food.
Although we don’t know where the Japanese whale shark swam from, long migrations for the species are well documented. Using satellite tags, scientists have found that whale sharks can swim thousands of kilometres in a matter of months (PDF). One female, appropriately dubbed ‘Rio Lady’, swam from the Gulf of Mexico to the middle of the Atlantic off Brazil in 5 months – roughly the distance from Vancouver to St. John’s, Newfoundland.
Sighting tropical species outside of their previous known range might become more common in the future. According to NOAA, the global average ocean temperature in June of 2014 was 0.64°C above the average for the 20th century, the highest for any June on record. For January-June, it was the 3rd warmest such period, trailing only 1998 and 2010. And these records are becoming the norm. As a consequence, warmer waters could lead to the ‘tropicalization’ of colder, temperate oceans, whereby marine species such as whale sharks shift their ranges as new habitats become liveable.
Off the Azores in the north Atlantic, whale sharks were quite rare until 2007, when fishermen around the islands reported a drastic increase. In that region, one study found that this upsurge in whale shark sightings was related to sea surface temperatures 22°C and above.
In another study, Ana Sequeira and colleagues reviewed whale shark sightings from tuna fishing vessels, and determined that suitable habitat for whale sharks would shift poleward in the Atlantic because of rising temperatures.
Will the whale shark become a regular visitor to Canada? Our waters, especially in the Pacific, are likely still too cold. But, if we keep on the current climate change trajectory, people on the Atlantic coast of Canada should keep their eyes peeled for the largest fish in the sea. Just don’t look in Lake Ontario.