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Atlantic Herring
 Herring Research: Using Acoustics to Count Fish

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Sonar detecting a school of fish (upper right). Expanding circles represent angled distance from the transponder. The large colored image along the top perimeter represents seafloor.
acoustic transducer
Towed body with acoustic transducer (shown underneath) and portable data logging hardware (above right).
onboard data storage
Several boats have transducers attached to their hulls and connect directly to onboard computers as shown above.
CTD probe
CTD (Conductivity, Temperature, Depth) probe before launch. Information from this sensor is used to determine environmental effects on observed fish stocks. These types of sensors are invaluable as they record with sub-meter resolution. Satellite imagery by comparison, below, provides resolution on the order of kilometers. (Kohl Kanwit photo)
Research Vessel trasect overlaying ocean temperature
Research vessel transects overlaying satellite data of ocean temperature.

Much of the current cooperative research between scientists and fishermen utilizes acoustics to study herring stocks. Acoustics is the study of the properties of sound - how it is created, transmitted, and received. Acoustic technology is especially well suited for underwater applications since sound travels farther and faster underwater than in air. The properties of sound traveling through seawater are important to the communication of many marine organisms as well as to human navigation, finding and catching fish, and fisheries research.

Historically, fishermen used many different techniques to hunt schools of fish. In addition to knowledge of migration patterns, they would watch for flocks of birds congregating above the fish schools or for the glow of phosphorescent waters as the school traveled by night.

The advent of hydroacoustic ("water-sound") technology, largely developed for naval purposes, revolutionized the commercial fishing industry as well as fisheries research. Sound waves travel differently through fish than through water because a fish's air-filled swim bladder is a different density than seawater. This density difference allows fishermen and scientists to remotely detect schools of fish using reflected sound.

Commercial fishing vessels rely almost completely on acoustic sonar (SOund Navigation And Ranging) to detect schools of fish. The reflected sound pressure wave is received and converted into an electrical signal visible on the vessel's sounder/sonar screen. The elapsed time between the transmit and receive signal provides range information, whereas the intensity of the return signal can provide information on the size and number of fish.

From acoustic information, herring fishermen are able to determine size, species, and position of their targeted species. Fishermen also use active sonar and echo sounder technology to determine water depth, bottom contour, and bottom composition. By working cooperatively with fishermen, scientists in the Gulf of Maine can refine and utilize this acoustic information to study herring populations. Ongoing acoustics-based herring research projects in Canada and the U.S. are described below.

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The Canadian Project

A program headed by Canadian researcher Dr. Gary Melvin of the Canadian Department of Fisheries and Oceans (DFO) Biological Station in St. Andrews, New Brunswick, was the first to incorporate acoustic data collection devices on herring boats. This "hands-free" approach to herring research is relatively inexpensive and minimizes the disturbance to normal fishing activities.

The Canadian herring industry and scientists from DFO collaborate on an "in season" management strategy based on acoustic surveys. The collaboration between scientists and fishermen involved the development of an automated acoustic logging system deployed on commercial fishing vessels in the Canadian Bay of Fundy/Scotian Shelf herring stock complex. This system automatically records location as determined by GPS readings and hydroacoustic information on herring schools.

The deployment of an automated acoustic logging device to record the fish biomass encountered by a fisherman was a crucial step towards integrating industry-based herring stock estimates and in-season fisheries management decisions. The Canadian program asks fishermen to conduct acoustic surveys on spawning grounds prior to fishing in order to estimate herring abundance. Catches were set at approximately 20% of the biomass observed in the pre-fishing survey. Today, the spawning ground survey data collected by fishermen play a key role in evaluation of stock status during the annual assessment. [1]

Once this quantity of fish has been removed, the Canadian fleet must demonstrate, through another acoustic survey, that there are sufficient herring to justify further fishing. If not, the area is closed and the fleet required to relocate to other fishing grounds. This Canadian management strategy has become known as the "Survey, assess, then Fish" protocol. [2, 3]

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The Gulf of Maine Aquarium (GMA) Project

One of the Gulf of Maine herring research priorities identified by the GMA-led forum of industry, research and management representatives was the need to develop a means of monitoring and assessing spawning stocks in the Gulf of Maine. The conveners decided upon a goal of developing an automated acoustic survey capability to assess herring stocks in U.S. waters of the Gulf of Maine.

Building on the Canadian effort, the Gulf of Maine Aquarium developed a pilot project in 1998 to collect acoustic data on herring aggregations in the course of normal fishing activities in U.S. waters. The data loggers used in Canada were installed on two fishing vessels, integrated with their existing acoustic sounder and navigational systems.

After editing and analyzing the acoustic data collected on herring fishing vessels, the GMA project allows researchers to assess the amount of herring detected along transects within the fishing vessels' path.

In the course of the project, an important distinction was drawn between fisheries-independent and fisheries dependent data. Vessels collecting fisheries-independent data are hired to conduct a survey using well ordered scientific transects. Vessels collecting fisheries-dependent data record information on herring biomass as they actively fish for herring.

While data obtained in a region devoid of herring is important information to a herring biologist, this only means empty fish holds for herring boat captains. In fisheries-dependent surveys, the vessel course is chosen by the captain to increase the likelihood of encountering fish.

In the fisheries-dependent survey, the school of herring is examined in more detail at a smaller spatial scale. This provides useful information such as the changes in the size and structure of herring schools as they are fished. The fisheries-independent scientific survey covers a large region in a systematic way and may reveal areas with no fish and schools missed by fishing surveys. It is useful for taking snapshots of fish populations over wide areas.

Overall, GMA's hydroacoustic survey project has supported the assertion that collaborative fisheries research using commercial fishing vessels is a viable method to collect acoustic data on Gulf of Maine herring stocks. Results from the fisheries independent surveys are integrated with other survey groups, such as the National Marine Fisheries Service (NMFS) and Canada's DFO. This provides an overview of herring stocks in the Gulf of Maine.

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The National Marine Fisheries Service, Northeast Fisheries Science Center (NEFSC) Project

"Northeast Fisheries Science Center's (NEFSC) acoustic research efforts during recent years have focused on improving fisheries-independent population estimates of Atlantic herring in the Georges Bank and Gulf of Maine regions for more cost-effective and timely fisheries management. Field experiments have been conducted to evaluate survey designs, improve variance estimators, and define species-specific individual target strength measurements.

"Laboratory experiments provide development, 3-D visualization, and validation of theoretical backscattering models for individual fish. Resources have also been allocated to test, evaluate, and improve advanced technologies (e.g., broadband, multibeam acoustics, theoretical backscatter modeling, neural network classifiers) in collaboration with industry, academics, and other government agencies for future implementation on NEFSC fisheries acoustic surveys." [4]

For more information on NEFSC acoustic projects, see the NEFSC Fisheries Acoustics Research Group website.

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Examples of Acoustic Data

As a fishing or research vessel logging acoustic data moves through the water, location information is matched to vertical acoustic snapshots of the water column every second. These snapshots (pings) form a continuous image as seen below, left. After manually editing out non-herring information, tailored software groups these "pings" to estimate biomass. These biomass estimates are then correlated to position and environmental data. Turning points in vessel tracks or transects are removed to avoid double counting of fish as seen in the images, below, right.

Acoustic Data Editing Software

Vessel Tracks and Transects

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[1] Melvin, G.D. Y. Li, L.A. Mayer, and A. Clay. (2002) Commercial fishing vessels, automatic acoustic logging systems and 3-D data visualization. ICES Journal of Marine Science. 59:179-190.

[2] Melvin, G.D., R. L. Stephenson, M. J. Power, F. J. Fife, and K. J. Clark. (2001) Industry acoustic surveys as the basis for in-season decisions in a co-management regime. In F. Funk, J. Blackburn, D. Hay, A. J. Paul, R. Stephenson, R. Toresen, and D. Witherell (eds.) (2001) Herring Expectations for a new millenium. University of Alaska Sea Grant, AK-SG-01-04, Fairbanks. 675-688.

[3] Melvin, G.D., J. Power, F.J. Fife, K.J. Clarke, and R. L. Stephenson. (2001) Summary of the 2000 herring acoustic surveys in NAFO Division 4WX. Canadian Stock Assessment Secretariat Res. Doc. 056: 41pp.

[4] NEFSC Fisheries Acoustics Research Group website, Research section.

General References:

Yund, Philip O. (1999-2000) Use of Automated Data Logging Systems To Survey Atlantic Herring In the Gulf of Maine. Gulf of Maine Aquarium, Project Report. 25 pp.

Yund, Philip O. (1998) Fishing Vessel Acoustic Survey of Gulf of Maine herring Stocks. Gulf of Maine Aquarium, Project report. 29 pp.