To help estimate fish populations, scientists experiment with seafloor-mounted sonar systems that monitor fish in the water column above
Shelikof Strait, in the Gulf of Alaska, is an important spawning area for walleye pollock, the target of the largest--and one of the most valuable--fisheries in the nation. This year, a team of NOAA Fisheries scientists went there to turn their usual view of the fishery upside-down.
The bottom-mounted sonars produce high-quality data. This image shows the abundance of pollock as viewed by the upward-looking sonar at a spawning site on March 15th, 2015. The colors in the image represent the strength of sound reflected from fish, with a strong echo from the sea surface visible at the top of the image.
Scientists have been conducting fish surveys in the Shelikof Strait for decades. They do that in part by riding around in a ship and using sonar systems--basically, fancy fish finders--to see what's beneath them. But in February of this year, scientists moored three sonar devices to the seafloor and pointed them up toward the surface. The devices have been recording the passage of fish above them ever since.
Because underwater devices cannot transmit data in real time, the sonar systems have been storing their data internally, leaving scientists in a state of suspense since February. But suspense turned to satisfaction last week when, working in cooperation with local fishermen aboard a 90-foot chartered fishing vessel, scientists retrieved the moorings from the bottom of Shelikof Strait.
"The data looked beautiful," said Alex De Robertis, a biologist with NOAA's Alaska Fisheries Science Center, shortly after he cracked open the unit and downloaded the data.
First Attempt with a New Technology
"This was a first trial," De Robertis said. "We're still developing the technology to see how well it works."
Whether moored on the bottom or carried by a ship, the sonar systems that scientists use work the same way: they emit a ping that echoes off the fish (and anything else in the water column). Based on the strength of the echo, scientists estimate the number of fish in the water. Those estimates are used when setting sustainable catch limits.
"Usually we estimate how many fish we have by reading the acoustic echo off their backs," said De Robertis. "In this case, we'll be reading the echo from their bellies."
But unlike shipboard sonar, moored sonars are stationary, so the tricky part is choosing the right mooring locations. De Robertis, along with NOAA Fisheries colleagues Chris Wilson and Robert Levine, have analyzed 20 years of survey data to select the three locations used in this study, which they hope will prove representative of the larger Shelikof Strait area.
A Long-term Perspective
If the technology works, scientists could use it to augment traditional, ship-based surveys. In addition to using sonar, those surveys also involve catching a sample of fish with a trawl, which produces information on the age, size, and physical condition of the fish. However, those surveys offer only a snapshot of what's happening in the water during the time of the survey. In years when the fish aggregate earlier or later than usual, the ship-based surveys might miss some of the action.
The experimental sonar system, on the other hand, records over long periods--3 months long in the case of the experimental deployment in Shelikof Strait.
"This will give us a new window on what fish populations are doing over time that we wouldn't be able to get any other way," De Robertis said. Scientists will just have to get used to the fact that the window is upside down.
Marjorie Mooney-Seuss | EurekAlert!
Researchers discover natural product that could lead to new class of commercial herbicide
16.07.2018 | UCLA Samueli School of Engineering
Advance warning system via cell phone app: Avoiding extreme weather damage in agriculture
12.07.2018 | Leibniz-Zentrum für Agrarlandschaftsforschung (ZALF) e.V.
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences