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U.S. Geological Survey - Great Lakes Science Center

Sounding the depths of the Great Lakes food webs: GLSC hydroacoustics

Echosounder data display off Grand Marais on the south shore of Lake Superior.

Daniel Yule, a USGS Great Lakes Science Center (GLSC) Research Biologist in Ashland, Wisconsin, traveled to Thonon, France, for the month of April, 2016, to work with fisheries scientists Drs. Jean Guillard and Orlane Anneville of the Institute of National Agricultural Research - Center of Alpine Lake Research (INRA CARRTEL). Guillard and Anneville invited Dan because of his expertise with a maturing technology called hydroacoustics. This technology uses sound waves to assess fish populations throughout the water column. It is much like a scientific-grade fish finder.

The binational research team wanted to understand why survival of larval (baby) whitefish in large, northern lakes can vary so greatly from one year to the next. To meet this goal they needed to develop a rapid method of assessing the zooplankton (food) available to larval fish after hatching. The team sampled Lake Geneva six times using five hydroacoustic frequencies (38-, 70-, 123-, 208- and 430-kHz), larval fish trawl nets, and fine-mesh zooplankton nets. Researchers have long used nets to measure zooplankton availability, but only small volumes of water can be sampled using this method, and counting zooplankton under microscopes is slow, labor intensive, and expensive. Alternatively, hydroacoustic methods may allow for rapid assessment of zooplankton available to whitefish larvae over much larger volumes of water in a much more efficient manner.

Preliminary results from the study indicate that acoustic methods can be used to measure zooplankton abundance in freshwater, particularly when using the 123-, 208-, and 430-kHz frequencies. The project, which was funded by a Visiting Scientist Grant obtained through the University of Savoie Mont Blanc, will continue next spring in North America on Lake Superior through a partnership with the Grand Portage Band of Lake Superior Chippewa. The INRA CARRTEL released a description of the project on their website, “Le CARRTEL accueille Daniel Yule, scientifique américain du Great Lakes Science Center.”

GLSC hydroacoustic work in the Great Lakes

The GLSC has a large research vessel and teams of research biologists on each of the Great Lakes. Biologists across the GLSC have used hydroacoustic technology on the Great Lakes since the early 1990s. As of 2014, all five of GLSC’s large research vessels are equipped with this technology.

David Warner, GLSC Research Biologist, and Biological Science Technician Timothy O’Brien (Ann Arbor, Michigan) conduct hydroacoustic surveys on lakes Michigan and Huron to understand lakewide patterns in abundance, distribution, life history, and interactions of pelagic (open-water) fish communities. They conduct sampling combining hydroacoustics and a variety of trawl nets and limnological samplers.

These surveys on lakes Michigan and Huron are collaborative in nature, incorporating efforts by the GLSC, Michigan Department of Natural Resources, and the U.S. Fish and Wildlife Service. The information gathered is used to inform fishery management decisions, such as setting stocking rates for sport fish or harvest quotas for species like bloater.

The alewife is an important prey fish species in Lake Michigan supporting the sport fishery. Information from hydroacoustic surveys, bottom trawl surveys, and estimates of predator consumption of alewives are used in a “stock assessment model” to estimate lakewide biomass of the prey fish. The biomass of Chinook salmon is divided by the alewife biomass to generate a predator-prey ratio. For example, 1 kg of Chinook to 10 kg of alewife equals a predator-prey ratio of 1/10, or 0.1.  On Lake Michigan, this ratio is used to inform stocking decisions aimed at keep the abundance of predators and prey in balance throughout the system to ensure a sustainable fishery.

On Lake Ontario, GLSC Research Biologists Maureen Walsh and Brian Weidel (Oswego, New York), are using hydroacoustic technology to better understand alewife seasonal distribution, both lakewide and along a nearshore-to-offshore gradient. They are also investigating changes in daily, vertical distribution of alewives. This work is done in collaboration with colleagues from the Ontario Ministry of Natural Resources and Forestry, the New York State Department of Environmental Conservation, and Cornell University. Walsh and Weidel used hydroacoustics during a recent spring bottom trawl survey to compare virtual hydroacoustic “catches” to actual bottom trawl catches. In late summer of 2016, they paired hydroacoustics and midwater trawl sampling to better understand native Lake Ontario cisco and bloater populations, two native species that are found in low numbers and are currently targeted for restoration. 

On Lake Erie, GLSC Research Biologist Patrick Kocovsky (Sandusky, Ohio) works with state and provincial partners to conduct annual surveys in all three basins of the lake. Typically, Kocovsky’s work focuses on the central basin where surveys have been conducted for eleven years. The primary management objective of the lakewide effort is to determine abundance of rainbow smelt, which comprise a commercial fishery in Ontario, and other prey fishes that support the binational yellow perch and walleye fisheries.

In addition to these management outcomes, Kocovsky has developed a research program combining survey data, data from experiments, and hydroacoustic methods. One effort includes assessing the effects of standard procedures for collection and analysis of hydroacoustic data on estimates of fish density, which he studies in collaboration with Dan Yule and David Warner. Kocovsky also looks at the effects of standard procedures for collection of data when fish densities are extremely high, such as in Lake Erie which supports the largest recreational fishery of all the Great Lakes and a larger commercial fishery than the other four lakes combined. He also studies how large, hydroacoustic-equipped research vessels affect the behavior of fish under the boat during surveys.

One innovative application of Kocovsky’s hydroacoustics expertise is for research on Asian carp, a potential Great Lakes invasive species advancing from the south. One possible method of blocking the northern advance of Asian carp is the use of sound walls across canals. Kocovsky has applied hydroacoustic data analysis techniques to assessing behavior of Asian carp to these sound deterrents. 

Filling in the gaps: A little background on hydroacoustics

The main components of hydroacoustic technology are a transducer and an echosounder. Transducers emit a sound wave at a particular frequency into the water which spreads out in the form of a cone. The size of the cone is determined by the transducer’s specific beam angle: the larger the angle, the greater the sample volume. When a wave emitted by the transducer encounters an object in the water column (for example, zooplankton or a fish), a portion of the sound is reflected off the object back toward the transducer. The echosounder is responsible for creating the original electrical signal that is passed along to the transducer as well as receiving the final information back from the transducer and producing an output file that can be analyzed by researchers. Hydroacoustic surveys utilize this ability to “remotely sense” the presence and number of organisms in a given area in order to assess populations of zooplankton, small invertebrate organisms, and pelagic fish.

To ensure accuracy, hydroacoustic results are verified by simultaneously deploying various trawl net samplers. By matching hydroacoustic data to actual catch data from the trawl samplers, biologists can ground-truth the hydroacoustic data and more accurately estimate populations of organisms.

In recent years, oceanographic researchers have been testing the simultaneous use of multiple frequencies through multiple transducers in a single study (for example, see photo of Dan Yule on Lake Geneva). The end goal is to monitor in a single survey all the important components of an aquatic ecosystem: zooplankton, small invertebrates, and fish. GLSC’s David Warner and Dan Yule have begun to introduce this approach in the Great Lakes. We’ll cover that topic in future Top Stories.

For more information about GLSC hydroacoustic research, contact Daniel Yule (Lake Superior, dyule@usgs.gov), Dave Warner (Lake Michigan, dwarner@usgs.gov), Timothy O’Brien (Lake Huron, tiobrien@usgs.gov), Patrick Kocovsky (Lake Erie, pkocovsky@usgs.gov), or Maureen Walsh (Lake Ontario, mwalsh@usgs.gov).  

Photo Credit: 
Dan Yule, USGS.

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