chrispeng [ad_1]
A group of researchers used wireless sensors to understand the unknown underwater migration world of European eels. By tracking the migration of eels from Europe to the sea of algae (located in the middle of the North Atlantic) every year, scientists at the National Institute of Marine Resources of the Danish University of Science and Technology hope to understand the status of the eels’ migration routes and speculate why the number of eels is declining rapidly.
These tests are part of the large scientific research project Eeliad, and Eeliad focuses on how to better understand European eels and increase their numbers. The project includes tracking eels in the ocean, freshwater and brackish freshwater to understand the living environment of this fish.
Danish scientists speculate that eels leave the European coast every autumn, travel about 3,000 miles, and arrive at the sea of algae in spring. However, since no eels migrating can be seen in the ocean, it is impossible to confirm their exact route, or even whether the sea of algae is their destination. In order to understand the migration route, the researchers hope to not only measure the location and distance of the eels when they migrate, but also understand the depth and temperature of the sea water they pass through.
However, there is currently almost no technology to track underwater animals. “We have encountered an interesting problem.” Senior researcher Kim Aarestrup said that RF and satellite signals cannot pass through salt water, so sensors and transmitters must float on the surface to be read, while eels can be underwater for thousands of Rice swims, and it does not float on the ocean surface during migration. In the fall of 2006, the researchers decided to try the battery-powered X-tag off-satellite tag (PSAT), which is manufactured by Microwave Telemetry, a Maryland animal tracking product company. The tag is about 4 inches long and can be mounted on the back of an eel.
The researchers selected 22 of the largest eels from 100,000 eels (caught by fishermen from Ireland during their freshwater migration downstream). These selected eels weigh about 5 pounds on average (usually eels weigh about 1 pound) to ensure that they are strong enough to carry the sensor. The scientists installed the tag on each eel by inserting a metal wire on the upper back of the animal (in front of the dorsal fin), and placed a protective pad around it, installed the tag on the pad, and then released the eel.
The researchers selected 22 of the largest eels
The sensor on the tag collects the depth, temperature and brightness of the surrounding environment every two minutes, and the tag stores these data in its 64-megabyte flash memory. The tags are compiled with a release mechanism that releases the tags at different times during the migration of the eels-some are 1 month apart, others are 2 months, or 3, 4 months. If the tag drops to 1250 meters underwater (it will damage the tag) or the depth read for 4 consecutive days (this means the eel may have died), the tag will be released automatically.
Battery-powered X-tag tag
Once detached from the eel, the tag floats on the water and begins to send a 401.65 MHz signal, including its unique ID code and sensor data. The signal is received by the Argos low-altitude satellite. In order to calculate the position of the tag, the system measures the frequency transition of the signal received by the satellite passing the tag-this phenomenon is called the Doppler effect. Scientists can use the Argos global network to obtain data through user names and passwords, and the system can also send emails to scientists to remind the sensor to float on the water.
The results of the study do not allow scientists to understand the entire migration process of eels. However, from the point of departure, the system did track eels for 1,300 kilometers. Fourteen of the 22 tags sent signals, proving that the fish was drifting along the Atlantic Ocean, and the eight tags that did not send a signal might sink to the bottom of the sea, or in the stomachs of other marine predators, or fail to function properly.
Research results indicate that eels may swim 5-25 kilometers a day, Aarestrup said. This is much less than the expected 35 kilometers per day (the speed required to reach the sea of algae in April). It may be that the tag has slowed down the eel, or the eel itself may take more time to reach the algae-researchers may have to re-estimate the migration distance. “At present, we have not ruled out any factors,” he said.
The data shows that the eel swims about 650 feet underwater at night and sinks to 2,000 feet during the day. Researchers believe that falling to cooler water will delay the sexual maturity of eels until they reach the spawning ground.
Because the cost of the label is relatively high ($4,000 per piece), researchers only label 22 eels. Scientists plan to label eels departing from Sweden in the fall of 2010, and hope to adopt smaller and cheaper labels by then. Currently, the team has not decided how many tags to use.
[ad_2]
