Juvenile Salmon Shark Stranding 2009

A juvenile salmon shark (Lamna ditropis) washed up on North Chesterman’s beach on August 20th, 2009. Jim Darling, a local biologist reported the shark and took the attached photo. The shark was approximately one metre long and birds had already begun scavenging the carcass.

The stranding of juvenile salmon sharks is a common occurrence in summer months along the west coast of Vancouver Island. Since 2005 we have received ten separate reports of juvenile salmon sharks strandings ranging from the Juan de Fuca trail to Chesterman’s beach in Tofino. We usually receive at least one salmon shark stranding report per year, but in 2007 a total of four separate stranding were reported. This salmon shark stranding is the first report we received this year.

So the question you’re probably asking is why do sharks strand themselves? There is no single definitive answer, but a range of hypotheses that have been put forward. Some of these hypotheses include a sudden change in water temperature, stormy ocean conditions, disease, ingestion of flotsam (garbage), or pursing prey. Another interesting comparison discusses the possibility of local geomagnetic signatures confusing the navigational abilities of sharks (check out this link for further discussion http://www.elasmo-research.org/education/topics/b_strandings.htm). A final noteworthy item is that live shark strandings are usually recorded for juveniles; juvenile salmon sharks along the Pacific Northeast and juvenile whale sharks along South African coasts. Perhaps inexperience or poorly developed navigational abilities may also contribute to these strandings. In the end it is still a mystery and shark biologists around the world continue to study this phenomenon and hope to find more definite answers.

If you have any shark or skate sightings to report we would love to hear from you. You can email us at shark_reports_bc@yahoo.ca.

Spiny Dogfish Sharks

The warm summer waters off the West coast of Vancouver Island bring in a large number of shark species. The most common and abundant shark is the spiny dogfish shark (Squalus acanthias). This post was inspired by a unique scuba diving experience I had in about 40ft of water on a rocky reef in Barkley Sound. A curious female spiny dogfish shark about 1.25 metres long came swimming out of the murky depths. She circled back quite a few times and even swam right under me while I took these photos. Spiny dogfish sharks don't get much bigger than this one and they are often found in schools. However, this female shark was solitary and for the two days I dove the site and saw her both times. Quite a remarkable experience!

Spiny dogfish sharks are often underappreciated in the world of sharks. They are the most common and abundant sharks the North Pacific Ocean. Recreational fishers trolling for salmon in the summer months frequently catch these sharks. Their razor sharp teeth cut fishing line and the misconception that they are preying on salmon give them the bad reputation as a "trash fish". But this is no trash fish; these sharks possess some remarkable life history traits and behaviours. This is a highly migratory species where individuals tagged off the West coast of Vancouver Island were actually caught a year later off the coast of Japan! The spiny dogfish shark is also one of the most long-lived shark species, reaching an age of at least 80 years and females do not become reproductive until 35 years of age. The females also have an extremely long gestation period (fertilization to birth) - 22 months! This rivals the gestation period of the Asiatic elephant. A unique and fascinating member of the shark world - the spiny dogfish shark!