Photo: Pacific Underwater: Halibut - The story of the sideways swimmer

Halibut on left, cod on right. (Credit: New Westminster Archives)

By Kat Middleton, Western Region Science & Policy Intern

During the late 1800s and early 1900s, thickly moustachioed fishers in hats and plaid plied the waters off Vancouver's Stanley Park in small, wooden boats, part of Canada's first commercial Pacific halibut fishery. Using hand-held lines, they caught record numbers and sizes of halibut right in the harbour.

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The largest flatfish in the world, Pacific halibut can weigh up to 300 kilograms and measure three metres in length. Despite their daunting size, these diamond-shaped fish are masters of disguise.

During the early stages of their life, halibut swim like regular fish. As they grow, juveniles begin swimming sideways and their lower eyes gradually migrate to their top side—typically the "right"—of their bodies. This helps them bury themselves in the sand for camouflage on the seafloor. Their green-, brown-, and black-spotted upper halves blend into the environment, allowing only their bulbous eyes to protrude above the sand, looking out for predators and prey. Their undersides—typically "left"—are light-coloured, almost white, camouflaging them from predators if they swim towards the surface.

Pacific halibut may not be the most beautiful fish in British Columbian coastal waters, but many think they are one of the most delicious—maybe they're so good deep-fried because they're so deep-dwelling!

Although they spend most of the summer months in shallower waters feeding off sandy seafloor habitats along our coast, in the fall Pacific halibut begin a seasonal migration to spawning grounds in deep, dark waters off B.C.'s continental shelf. Spawning occurs from November to March at depths upward of 400 metres, where each female halibut can lay millions of eggs. Once fertilized by a male, the eggs float up to the surface, and then hatch into microscopic larvae after a few weeks. Young halibut larvae can't swim; ocean currents carry them through the water, where they find plankton to eat. During the first few months of their lives, they go through the drastic changes that flatten their bodies. Then they begin settling on the sandy seafloor in shallower waters along the B.C. coastline.

Although no longer commercially caught right off Vancouver, halibut populations in B.C. have increased in recent years. With better fisheries management, including a strong network of protected areas, there is good reason to hope for continued increases of this weird and wonderful fish.

November 16, 2013

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