Patent no. 147. Filing year 1869.
"Improvements in Machines By Which Fish Are Enabled to Surmount and Pass Dams, Cascades and Other Obstructions in Water," J.W. King.
A fish ladder, or fishway, is a man-made solution to a man-made problem. Certain types of fish, such as salmon, migrate to their breeding grounds each year to mate. Blocking the waterway to their breeding ground with a dam or similar obstacle can decimate the species population. A fishway is a series of low "steps," around or through a barrier, that fish can navigate, by swimming and leaping, to access the waters beyond. The first rudimentary fishways were constructed in France in the 17th century, but with the Industrial Age came more dams and other obstructions in rivers, increasing the need for fishways.
James W. King of Shubenacadie, Nova Scotia, patented his fish ladder, above, in 1869. The ladder contained a series of gravel-bedded switchbacks running its length, and an upper "deck" that was flush with the higher body of water. This deck was held up by columns that contained tanks, which also demarked the switchbacks. Water from the top deck filled the tanks, which in their turns released water into the switchbacks. As shown in the patent drawing, water flowed downhill through the switchbacks, but water from the vertical tanks was released in the opposite direction. The contrary flow of water slowed the downward flow, calming the water enough for fish to make their ascent.
With fishways, adaptability is a virtue. They often need to be tailor-made to match local geography and the type of obstacle, as well as the type of fish, involved. One of the more effective designs, the Denil Fishway, originally developed in 1909 by a Belgian scientist, is a ramp containing a series of closely spaced baffles that slow and redirect the water. The spacing of the baffles can be adjusted to suit the size of the fish or the speed of the water. This last criteria is important, since the water needs to flow fast enough to attract the fish and provide migration "cues," but not so fast that the fish can't climb it.
Some types of fishways in use today employ switchbacks similar to those in King's design. King maintained that his fish ladder was adaptable, but its sophisticated construction -- requiring a second level and the proper positioning of tank openings -- would have made subtle adjustment difficult. The fishways in use today are, for the most part, simple-looking arrangements of baffles and switchbacks, though that simplicity can be deceptive: a salmon fishway constructed in 2001 around a dam near Wolfville, Nova Scotia, cost $1 million to build.
It is possible that King's fish ladder was built to suit a local need. Other Canadian patents for fishways between 1869 and 1894 include two by King's fellow Nova Scotian, William Henry Rogers. Rogers' first fishway, patented in 1880 (no. 11271), was a simple ramp and baffle arrangement, like the Denil Fishway, that was apparently used locally. The second, patented in 1888 (no. 29653) was a more sophisticated gated design, resembling locks for fish.
Of course, fishways were not constructed purely out of concern for the fishes' plight, but with the local fishing industry in mind. Still, they are considerably more humane than other Canadian fish-industry patents, such as McNab's floating fish net, patented in 1872 (no. 1382). His net, which stretched from the river or sea bed to the surface, was designed to catch "porpoises, seals and fish," as well as anything else that happened along -- an approach to fishing that is today considered quite wasteful and damaging to the balance of the food chain in the world's oceans.
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"How Can Dams and Associated Structures Affect Fish Migration?" The Canadian Dam Association's Frequently Asked Questions.
www.cda.ca/cda/main/faqdameffects.htm (accessed November 10, 2005).
"The Fishladder at White Rock." Nova Scotia Power: About Us.
HowWeGeneratePower/FishLadders.html (accessed November 10, 2005).