Sharks Among Us #1 – The Blue Shark

By The Marine Detective on August 1, 2010

The image below is of a Pacific Blue Shark (Prionace glauca) being rescued by Lindsey Pattinson of Tiderip Grizzly Tours on July 15th, 2010 in Glendale Cove, British Columbia.

Many British Columbians are unaware that we have at least 13 species of shark among us, ranging from the smaller species such as the Spiny Dogfish up to the 6-gill shark (5 m+) and the very, very rare Basking Shark (9 m+). The beautiful Blue Shark reaches a maximum of 3.8 meters and is distinct in its deep blue colouration and slender shape.

The Slue Shark is common in B.C. and is, in fact, extremely far ranging and widespread. It is found from Alaska to Chile in the Pacific but is also present in the Atlantic and Indian Oceans.  It has been found in waters from 7 to 16°C, latitudes of 60°N to 50°S and from the shallows to depths of 350 m (being more often at depth in warmer waters).

In researching the species after Lindsey’s find, I discovered that Blue Sharks undertake very large migrations, reportedly up to 9,200 km, moving north in the summer months.  More females than males move to the higher latitudes.

But, of course a sighting like this in Glendale Cove is an enormous rarity. Even with the Blue Shark being common in B.C., they are more often oceanic, on the continental shelf . . . not on the beach in Glendale!

For whatever reason, the animal stranded there and Lindsey cared enough to do what he could to save it.  Many shark species need to keep swimming in order to have oxygen-rich water pass over their gills. Knowing this, Lindsey moved the stranded shark back and forth in the water, forcing water over its gills and indeed, he revived it. He and the tourists he was guiding on the Grizzly Bear (and shark) watching trip had the joy of watching the animal swim to depth.

Thanks to Lindsey, this Blue Shark will be able to have more days of feeding on anchovy, mackerel, salmon, hake, dogfish, crustaceans and squid. It may also scavenge here and there and even feed on aggregations of krill by straining the water in the way a baleen whale would.

I suspect the Glendale Cove shark was a female and with Blue Sharks being a very prolific species, now saved, she could go on to bear 25 to 50 pups at a time (apparently even as many as 135)!  These young would grow inside her as the blue shark is “viviparous”, meaning they bear fully formed young. The pups are 35 to 44 cm at birth.

I was fascinated to learn that blue shark females can apparently “get pregnant” up to 20 months AFTER mating. They can store sperm packets in special glands in their reproductive tract called “shell glands” (aka nidamental glands) and pass their eggs through these glands to get fertilized.

If the rescued Blue Shark was indeed female, she may not have been able to feel much of Lindsey’s caring touch since the females are up to 3 times thicker skinned that the males! This adaptation is believed to allow the females to deal with the males since there is a lot of biting during courtship.

Unfortunately, the fate of Blue Sharks can also be to become the bycatch of longline and driftnet fisheries. One source reported that in one year alone (1990) “it is conservatively estimated that by-catch of blue sharks taken by the Japanese squid fleet in the North Pacific totalled 700,000.”

Further life history: Males sexually mature at 4–6 and females at 5–7 years. Believed to live to age 20.

For more photos of the blue shark rescue, click here.

Great thanks to Nick and Sue Spiller for sharing these photos.

Sources include:

• Biology of Sharks and Rays – ReefQuest Centre for Shark Research
• Sharks of the Pacific Northwest
• ICUN Red List of Threatened Species