Tuesday, October 09, 2012

A ladder for fishes

Woodhus Creek, part II. (First post)

The wide, sandstone-paved section of Woodhus Creek ends abruptly, top and bottom, entering and leaving through narrow openings in the forest.

Looking upstream. The creek flows from that black hole in the centre.

This was our special place, a room built for us by Ma Nature, unspoiled ... but, no; what's that wall at the right side?

Solid cement walls. No sandstone here.

A fish ladder, about two feet high, with strong cement baffles. It goes from the middle of the flats, up and around the bend, disappearing at the entrance to the bush.

Gentle stream, outside the barrier.

But why is a ladder needed here, where the water flows sedately over smooth stones, meandering from pool to still pool? A spawning salmon could climb this in his sleep! A minnow could navigate it! Why put a fishway here, of all places?

It might help to look at our 2010 photos. We came in June, while the spring floods were not fully abated. A good part of the creek bed was still underwater. And some of this water was white.

A few dry patches, a bit of turbulence. Nothing major, though.

Google maps helped a bit. The creek runs downhill through a narrow, deep gorge, turns a sharp corner, and spills onto the sandstone at high pressure.

Google photo; from the highway, 600 feet above our spot, the creek funnels down to its mouth.

Turbulence and jagged stones, just below the entrance.

In the fall, Coho salmon and cutthroat trout* come up to spawn in the shallow streams beyond the freeway. The water is deeper here then, up to the top of the ladder. It races out of the gorge, and hits a confusing choice of channels. Look closely at the photo above; water enters that pothole from three different angles, churning around as it finds the exit. Now imagine two feet of water above that.

These are smallish fish; the adult Coho averages about 8 pounds and a bit over 2 feet long. The cutthroat trout goes from 1 to 4 pounds, and up to 20 inches long. (Compare with the Chinook salmon; over 30 pounds and 3 feet long.) Both spawn in small streams, where the hatchlings and fry are protected from larger fish.

The Woodhus Creek salmon have grown to adulthood in the ocean. When the cold weather comes, they head up the Oyster River to the entrance to the creek, then up the canyon to the watershed above the highway, always coming back to the streamlet where they hatched. The stocks have been in decline in recent years; the cutthroat trout is blue-listed in BC, the Coho is yellow-listed and endangered. They need all the help they can get.

How the fish ladder works: this ladder is a Vertical Slot Fishway. It slopes upward, divided into individual "rooms", each opening onto the next on the perpendicular to the direction of the stream. This creates doorways with strong enough current to orient the fish, and corners with little current, for a resting spot. The total flow is longer than the stream bed, which makes the slope less pronounced.

Detail of the ladder. Even a small cutthroat can make it safely home here.

Ok. I'll go with what I wrote above: "a room built for us by Ma Nature, unspoiled ...". With the addition of the builders of the fishway, ORES. The salmon and we thank you!

*Oncorhynchus is a genus of fish in the family Salmonidae; it contains the Pacific salmons and Pacific trouts. The name of the genus is derived from the Greek onkos ("hook") and rynchos ("nose"), in reference to the hooked jaws of males in the mating season (the "kype"). (Wikipedia)

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