Several years ago, Rachel Lopez, now a senior at Rio Rancho High School in New Mexico, learned that large numbers of seals, whales, dolphins, turtles, and other creatures get caught in abandoned fishing nets every year. “In 2006, more than 30,000 fur seals were killed off the Pacific Coast because of [abandoned] nets. It is a growing problem,” she says. That prompted Rachel to focus her science fair project every year since then on finding a better net.
Rachel knew her project was an important one: A recent study by the United Nations estimates that approximately 640,000 metric tons of abandoned fishing gear, such as nets, traps, and fishing line, clutter the world’s oceans. Most fishing nets are made of plastic that is not biodegradable. That means the stray nets, called ghost nets, can snag unsuspecting marine life for years.
Over the past three years, Rachel has been testing a variety of natural fibers to see how they compare with the plastic used in fishing nets today, and if they could withstand the ocean’s salty waters. Rachel’s well-designed experiment and organized data tables and graphs earned her a trip to the Intel Engineering and Science Fair in Atlanta, Georgia, last spring. Turn the page to read more about her project.
Fishermen often use plastic nets because they rarely break or overstretch under the weight of their catch. Rachel knew that an alternative netting would have to be as strong as plastic and also resist strain (change in length) over time as well as plastic does.
Knowing that plastic would serve as her control, or the standard against which she would compare the natural fibers, Rachel began her search for potential replacement fibers in her own backyard. The New Mexico landscape is studded with yucca plants, which thrive in the desert. The long spiky yucca leaves contain strong fibers that support the tough leaves as they grow. Rachel decided that these fibers might be a good candidate for her experiment.
Once she had singled out yucca as a potential fiber, she realized that there were several types of yucca plants. She chose to test palm yucca, soapweed yucca, and strands made from a combination of fibers from both of these plants. Based on her results from previous years’ science fairs, in which palm yucca was a top performer against other fibers, Rachel came up with a hypothesis: Palm yucca fiber would be the strongest and most able to resist strain, malting it the best candidate to replace plastic in fishing nets.
STRETCHING IT OUT
To obtain yucca fibers, Rachel soaked yucca leaves in water until they started to rot. Then, she allowed the plant’s leaves to dry out so she could access the strong fibers inside. Next, she collected the fibers and twisted them into 66 ropelike test strands of palm yucca, soapweed yucca, and a combination of palm and soapweed yucca. Each test strand was 8 centimeters (roughly 3 inches) long.
Using sea salt and distilled water, she mixed up some homemade salt water and divided it equally among 66 jars. Rachel submerged one strand of fiber in each jar of salt water.
She set aside nine of the jars–three containing palm yucca strands, three containing soapweed yucca strands, and three containing the combination strands to test strain over the next month. To test the fibers’ strain, she built a tensile machine. A tensile machine is a device that holds a material in place vertically and uses weights to stretch it out. Every two days, she removed the nine test strands from the salt water and straightened them in the tensile machine so she could accurately measure their length. Then, she could easily determine any change in the fibers’ length over time that occurred due to contact with the salt water.
Rachel used the same machine to test the strength of the remaining 57 strands of fiber. Each week, she took three strands of palm yucca, three strands of soapweed yucca, and three strands of the combination fibers out of their jars, and added weights to the bottom of each of them until the strands broke. She then recorded the weight that caused the strands to break.
To keep all that dam organized, Rachel created a data table (see chart, p. 15). After a month of monitoring the strain and testing the strength of her strands, Rachel was ready to analyze her data. She used the information in her tables to create a line graph (see graph, p. 15) showing the average length of each type of fiber over the course of the month.
In her graph, the x-axis displayed the amount of time that had passed. The y-axis represented the average change in the fiber strands’ length, which was a dependent variable, or the factor that responded to the change in fiber type–the independent variable. Using a color key, Rachel plotted the average strain from each type of fiber: palm yucca, soapweed yucca, and the combination of palm and soapweed yuccas.
THE NET RESULTS
Although Rachel had hypothesized that palm yucca would beat out the other fibers, it turned out that strands made from the combination of the two fibers were the strongest. “I’m sure that they have different components that work together to make the combination stronger,” says Rachel.
Her data showed that all three fibers displayed the same average percentage of strain over the month they spent in the salt water; but when it came to strength, the combination strands beat the other two strands of fibers each week.
Now that Rachel has a promising candidate to replace plastic in fishing nets, she wants to learn more about how she can help solve the problem of ghost nets. This summer, she left her landlocked New Mexico home to meet with marine biologists and environmental engineers in coastal New Hampshire to work with them on a solution.
Rachel measured the change. In the length of her test strands over a period of one month. This table shows the average change In length for each type of strand. On which dates were all three types of test strand the same average length?
Average Length of Test Strands (centimeters) DATE PALM SOAPWEED COMBINATION 2/7/09 8 8 8 2/11/09 8 8 8 2/15/09 8.3 8.5 8 2/19/09 8.83 8.83 8.67 2/23/09 9.17 9.17 9 2/27/09 9.5 9.67 9.5 3/3/09 9.83 9.83 9.83 3/7/09 10 10 10
Rachel made a line graph showing how the length of the test strands changed over time. On February 16, 2009, which type of strand was still 8 centimeters long?