Last summer employees at the Dworshak National Fish Hatchery in Idaho undertook an experiment to test the effectiveness of shade cloth on fish held in raceways at the facility.
During the summer it can get upwards of 43°C (110°F) at Dworshak. And while the fish remain comfortable in their 7.5°C (45°F) water, the staff tends to wither in the heat. Thus, the first benefit was that it was much more comfortable for staff working under the shade cloth - it felt much cooler. The shade cloth also provided UV protection for the employees.
Shade cloth was installed over half of Dworshak's Spring Chinook "B-Bank" raceways (background) while half of the "A-Bank" raceways were left uncovered.
Shade cloth purchased from Christensen Net Works, (Everson, Washington) was installed over half of Dworshak’s Spring Chinook “B-Bank” raceways while half of the “A-Bank” raceways were left uncovered.
Four 20’ x 120’ cloth panels were installed by hatchery staff and Nez Perce Tribe Coho Interns over the raceways and hog-ringed onto the existing bird-netting structure. Each panel was pulled across the width of the structure and secured using bungee cords. Because of frequent winds staff wanted the shade panels to be able to break free from the bird-net structure rather than snapping the steel cables that hold the bird netting up.
Once the four panels were installed they were hog-ringed together to form one large sheet.
Installation of the panels was not without some issues: Panels tended to pucker at the center until they were hog-ringed together and during wind events, the hog rings holding panels together tended to break free. This has been alleviated, however, by the installation of grommets along the length of the panels.
One other concern was that the weight of the shade cloth caused the bird-netting to sag, lowering the overhead clearance of the B-bank raceways. This interfered with cleaning and netting morts. A track system is going to be installed so the shade cloth will be independent from the birdnetting. This should alleviate the sagging issue.
Following installation observations in fish behavior during feeding and use of raceways were made between the shaded and unshaded banks. Additionally, personal evaluations were made by employees working in both A and B banks.
It was evident that fish were more evenly dispersed in the shaded raceways. What’s more, algal growth was less aggressive in the shaded raceways and this made them easier to clean. Fish took feed better and fed more effectively in the shaded raceways.
In the unshaded raceways fish dispersed themselves along the pond walls and walkways. Fish were not as eager to take feed when presented and were overall more skiddish in the A-bank raceways.
The shade cloth was relatively easy to remove. The hog rings holding the cloth to the ends of the structure were removed and the cloth was pulled down in one big sheet. Several Idaho Youth Challenge crews assisted in assembly and removal of the shade cloth and removing the hog rings holding the panels together.
The preceding article was adapted from a poster prepared for the Northwest Fish Culture Conference by Angela Feldmann and LouAnn M. Lasswell.