Development of Multi-beam Sonar as a Fisheries Tool for Stock Assessment and the Identification of Essential Habitat of Atlantic Cod

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Project Type: 
Research
Project Number: 
R/CFR-12
Inception Date: 
2008
Completion Date: 
2010

Participants:

W. Huntting Howell UNH - Department of Biological Sciences Principal Investigator
Christopher Gurshin UNH - Department of Biological Sciences Co-Principal Investigator
Carl Bouchard Boat Captain Industry Partner
Charles Felch Boat Captain Industry Partner
J. Michael Jech National Marine Fisheries Service - Northeast Fisheries Science Center Collaborator
Larry Mayer UNH - Center for Coastal and Ocean Mapping Collaborator
Thomas Weber UNH - Center for Coastal and Ocean Mapping Collaborator

Students Involved:

Christopher Gurshin UNH - Department of Biological Sciences
Abstract: 

The purpose of the proposed research is to develop multi-beam sonar as a fisheries tool for characterizing spatial distribution, studying behavior, and assessing relative abundance of spawning cod aggregations for stock assessment, evaluation of time/area closures and identification of essential fish habitat. The importance of developing multi-beam sonar as a fisheries survey tool is warranted because multi-beam sonar has (1) a larger sample area or volume than single- or split-beam echosounders and trawls, (2) better spatial description, and (3) potentially fewer behavior-related sampling biases than traditional surveys. Relationships between acoustic backscatter and fish biology need to be understood before reliable acoustic surveys using multi-beam sonar can provide science-based information for stock assessments, identification of appropriate area closures and EFH designations of New England groundfish.

Spawning Atlantic cod, Gadus morhua, will be caught by commercial bottom trawlers and transferred live to a submersible net cage (100 m3), which also can be used as a surface pen. Hydrographic vessels will provide dockside support for acoustic data collection from three downward looking sonars mounted to a pole. A 300 kHz EM3002 multi-beam sonar and two EK60 split-beam scientific echosounders at 38 kHz and 120 kHz will acoustically sample a known population of cod of a known size in tandem. A series of ex situ experiments, using captive Atlantic cod will allow us to identify their acoustic “signature” and to study the relationship between acoustic backscatter and elements of their biology, including their abundance, behavior, depth, size, and co-occurrence of other species. Knowledge of the effect of density, size, depth, behavior and presence of other species is essential for using multi-beam sonar for in situ acoustic surveys for purpose of stock assessment and identification of essential fish habitat for Atlantic cod.

Objectives: 
1. Discriminate acoustic backscatter of cod from the cage.
 
2. Test if acoustic estimates of abundance is equal to or proportional to stocking density in the cage.
 
3. Determine if uncertainty (variance) of the acoustic estimate of abundance is equal among acoustic estimates at different stocking densities.
 
4. Determine if acoustic estimates of abundance vary at different depths.
 
5. Estimate TS distributions of cod.
 
6. Describe changes in acoustic backscatter due to decompression or compression of the swim bladder.
 
7. Estimate TS and acoustic estimates of abundance of different sizes of cod.
 
8. Determine change in cod stocking density acoustically.
 
Methodology: 

A 300 kHz EM3002 multi-beam sonar and two EK60 split-beam scientific echosounders at 38 kHz and 120 kHz will acoustically sample a known population of Atlantic cod of a known size in tandem. Cod (n=50,100, and 200) will be stocked in a submersible cage at three densities and lowered from surface to mid-depth and bottom depth to identify their acoustic “signature” and to study the relationship between acoustic backscatter and elements of their biology, including their abundance, behavior, depth, size, and co-occurrence of other species.

Rationale: 

The purpose of the proposed research is to develop multi-beam sonar as a fisheries tool for characterizing spatial distribution, studying behavior, and assessing relative abundance of spawning cod aggregations for stock assessment, evaluation of time/area closures and identification of essential fish habitat. The importance of developing multi-beam sonar as a fisheries survey tool is warranted because multi-beam sonar has (1) a larger sample area or volume than single- or split-beam echosounders and trawls, (2) better spatial description, and (3) potentially fewer behavior-related sampling biases than traditional surveys. Relationships between acoustic backscatter and fish biology need to be understood before reliable acoustic surveys using multi-beam sonar can provide science-based information for stock assessments, identification of appropriate area closures and EFH designations of New England groundfish.

A series of ex situ experiments using captive Atlantic cod will allow us to identify their acoustic “signature” and to study the relationship between acoustic backscatter and elements of their biology, including their abundance, behavior, depth, size, and co-occurrence of other species. Knowledge of the effect of density, size, depth, behavior and presence of other species is essential for using multi-beam sonar for in situ acoustic surveys by state and federal fisheries scientists for purpose of stock assessment and identification of essential fish habitat for Atlantic cod.

Accomplishments: 

2012

Researchers Calculate First Estimate of Spring-spawning Cod Biomass in Ipswich Bay
Atlantic cod populations experienced a collapse in the mid-1990s in the Gulf of Maine. Since that time resource managers and researchers have focused on finding improved methods of protecting cod populations and restoring them to sustainable levels. Using Sea Grant funds, researchers conducted surveys using multi-beam sonar to provide better estimates of cod population abundance and distribution than single- or split-beam echosounders and trawls. Based on their studies, researchers have calculated the first estimate of spring-spawning cod biomass in Ipswich Bay, Mass. This estimate provides more accurate information to help resource managers make better decisions about protecting the cod fishery and ensuring its future sustainability.

2010

 

 

Multi-beam Sonar Enhances Studies of Cod Abundance

 

RELEVANCE: Atlantic cod populations experienced a collapse in the mid-1990s in the Gulf of Maine. Since that time, management measures and research have focused on finding improved methods of protecting and restoring cod populations back to sustainable levels.

 

RESPONSE: Using Sea Grant funds, researchers conducted cage experiments and open water surveys using multi-beam sonar to identify the acoustic signature of cod and provide better estimates of cod population abundance and distribution than single- or split-beam echosounders and trawls.

 

RESULTS: Based in part on this research, the National Marine Fisheries Service established a cod spawning closure, prohibiting all fishing during the spawning season in the Whaleback area of the Western Gulf of Maine.

 

RECAP: Multi-beam sonar research has helped establish management measures aimed at protecting and restoring cod populations in the Gulf of Maine.

 

Publications

Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant

Journal Article

  • Gurshin, C., J. Jech, W. Howell, T. Weber and L. Mayer (2009). Measurements of acoustic backscatter and density of captive Atlantic cod with synchronized 300-kHz multibeam and 120-kHz split-beam echosounders. ICES Journal of Marine Science 66(6):1303-1309, July 2009.
  • Gurshin, C., W. Howell and J. Jech (2013). Synoptic acoustic and trawl surveys of spring-spawning Atlantic cod in the Gulf of Maine cod spawning protection area. Fisheries Research 141:44-61, April 2013.

Thesis/Dissertation

  • Gurshin, C. (2012). The use of multibeam and split-beam echo sounders for assessing biomass and distributin of spring-spawning Atlantic cod in the Gulf of Maine. Doctoral dissertation, University of New Hampshire.

Reports